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Climate influences near-surface biogeochemical processes and thereby determines the partitioning of carbon dioxide (CO2) in shale, and yet the controls on carbon (C) weathering fluxes remain poorly constrained. Using a dataset that characterizes biogeochemical responses to climate forcing in shale regolith, we implement a numerical model that describes the effects of water infiltration events, gas exchange, and temperature fluctuations on soil respiration and mineral weathering at a seasonal timescale. Our modeling approach allows us to quantitatively disentangle the controls of transient climate forcing and biogeochemical mechanisms on C partitioning. We find that ~3% of soil CO2 (1.02 mol C/m2/y) is exported to the subsurface during large infiltration events. Here, net atmospheric CO2 drawdown primarily occurs during spring snowmelt, governs the aqueous C exports (61%), and exceeds the CO2 flux generated by pyrite and petrogenic organic matter oxidation (~0.2 mol C/m2/y). We show that shale CO2 consumption results from the temporal coupling between soil microbial respiration and carbonate weathering. This coupling is driven by the impacts of hydrologic fluctuations on fresh organic matter availability and CO2 transport to the weathering front. Diffusion-limited transport of gases under transient hydrological conditions exerts an important control on CO2(g) egress patterns and thus must be considered when inferring soil CO2 drawdown from the gas phase composition. Our findings emphasize the importance of seasonal climate forcing in shaping the net contribution of shale weathering to terrestrial C fluxes and suggest that warmer conditions could reduce the potential for shale weathering to act as a CO2 sink.

Soil metabolomics is an emerging approach for profiling diverse small molecule metabolites, i.e., metabolomes, in the soil. Soil metabolites, including fatty acids, amino acids, lipids, organic acids, sugars, and volatile organic compounds, often contain essential nutrients such as nitrogen, phosphorus, and sulfur and are directly linked to soil biogeochemical cycles driven by soil microorganisms. This paper presents an overview of methods for analyzing soil metabolites and the state-of-the-art of soil metabolomics in relation to soil nutrient cycling. We describe important applications of metabolomics in studying soil carbon cycling and sequestration, and the response of soil organic pools to changing environmental conditions. This includes using metabolomics to provide new insights into the close relationships between soil microbiome and metabolome, as well as responses of soil metabolome to plant and environmental stresses such as soil contamination. We also highlight the advantage of using soil metabolomics to study the biogeochemical cycles of elements and suggest that future research needs to better understand factors driving soil function and health.

Estuarine wetlands harbor considerable carbon stocks, but rising sea levels could affect their ability to sequester soil carbon as well as their potential to emit methane (CH4). While sulfate loading from seawater intrusion may reduce CH4 production due to the higher energy yield of microbial sulfate reduction, existing studies suggest other factors are likely at play. Our study of 11 wetland complexes spanning a natural salinity and productivity gradient across the San Francisco Bay and Delta found that while CH4 fluxes generally declined with salinity, they were highest in oligohaline wetlands (ca. 3-ppt salinity). Methanogens and methanogenesis genes were weakly correlated with CH4 fluxes but alone did not explain the highest rates observed. Taxonomic and functional gene data suggested that other microbial guilds that influence carbon and nitrogen cycling need to be accounted for to better predict CH4 fluxes at landscape scales. Higher methane production occurring near the freshwater boundary with slight salinization (and sulfate incursion) might result from increased sulfate-reducing fermenter and syntrophic populations, which can produce substrates used by methanogens. Moreover, higher salinities can solubilize ionically bound ammonium abundant in the lower salinity wetland soils examined here, which could inhibit methanotrophs and potentially contribute to greater CH4 fluxes observed in oligohaline sediments.IMPORTANCELow-level salinity intrusion could increase CH4 flux in tidal freshwater wetlands, while higher levels of salinization might instead decrease CH4 fluxes. High CH4 emissions in oligohaline sites are concerning because seawater intrusion will cause tidal freshwater wetlands to become oligohaline. Methanogenesis genes alone did not account for landscape patterns of CH4 fluxes, suggesting mechanisms altering methanogenesis, methanotrophy, nitrogen cycling, and ammonium release, and increasing decomposition and syntrophic bacterial populations could contribute to increases in net CH4 flux at oligohaline salinities. Improved understanding of these influences on net CH4 emissions could improve restoration efforts and accounting of carbon sequestration in estuarine wetlands. More pristine reference sites may have older and more abundant organic matter with higher carbon:nitrogen compared to wetlands impacted by agricultural activity and may present different interactions between salinity and CH4. This distinction might be critical for modeling efforts to scale up biogeochemical process interactions in estuarine wetlands.

Background: Thinning practices are useful measures in forest management and play an essential role in maintaining ecological stability. However, the effects of thinning on the soil properties and microbial community in large Chinese fir timber plantations remain unknown. The purpose of this study was to investigate the changes in soil physicochemical properties and microbial community composition in topsoil (0–20 cm) under six different intensities (i.e., 300 (R300), 450 (R450), 600 (R600), 750 (R750) and 900 (R900) trees per hectare and 1650 (R1650) as a control) in a large Chinese fir timber plantation. Results: Compared with the CK treatment, thinning significantly altered the contents of soil organic carbon (SOC) and its fractions but not in a linear fashion; these indicators were highest in R900. In addition, thinning did not significantly affect the soil microbial community diversity indices but significantly affected the relative abundance of the core microbial community. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant bacterial phyla; the relative abundances of Proteobacteria and Acidobacteria were highest in R900, and that of Actinobacteria was lowest in R900. The dominant fungal phyla were Ascomycota, Basidiomycota and Mucoromycota; the relative abundance of Ascomycota was lowest in R900, and that of Mucoromycota was highest in R900. The fungal microbial community composition was more sensitive than the bacterial community composition. The activity of the carbon-cycling genes was not linearly correlated with thinning, and the abundance of C-cycle genes was highest in R900. Conclusions: These findings are important because they show that SOC and its fractions and the abundance of the soil microorganism community in large Chinese fir timber plantations can be significantly altered by thinning, thus affecting the capacity for carbon storage. These results may advance our understanding of how the density of large timber plantations could be modified to promote soil carbon storage. [ABSTRACT FROM AUTHOR]

An exponential rise in the atmospheric vapour pressure deficit (VPD) is among the most consequential impacts of climate change in terrestrial ecosystems. Rising VPD has negative and cascading effects on nearly all aspects of plant function including photosynthesis, water status, growth and survival. These responses are exacerbated by land–atmosphere interactions that couple VPD to soil water and govern the evolution of drought, affecting a range of ecosystem services including carbon uptake, biodiversity, the provisioning of water resources and crop yields. However, despite the global nature of this phenomenon, research on how to incorporate these impacts into resilient management regimes is largely in its infancy, due in part to the entanglement of VPD trends with those of other co‐evolving climate drivers. Here, we review the mechanistic bases of VPD impacts at a range of spatial scales, paying particular attention to the independent and interactive influence of VPD in the context of other environmental changes. We then evaluate the consequences of these impacts within key management contexts, including water resources, croplands, wildfire risk mitigation and management of natural grasslands and forests. We conclude with recommendations describing how management regimes could be altered to mitigate the otherwise highly deleterious consequences of rising VPD. Summary statement: Rising atmospheric vapour pressure deficit (or VPD) is one of the most widespread and significant consequences of climate warming for terrestrial ecosystems. This article reviews the mechanistic bases of these usually deleterious impacts and synthesises that information into a set of management recommendations to mitigate them. [ABSTRACT FROM AUTHOR]

• We firstly uncovered the functional gene variation under cadaverine and putrescine. • Cadaverine significantly reduced the diversity of C cycling genes. • Putrescine significantly increased diversity of C fixation genes only in sediment. • Total carbon and total nitrogen were negatively associated with C and N cycling. The response patterns of microbial functional genes involved in biogeochemical cycles to cadaver decay is a central topic of recent environmental sciences. However, the response mechanisms and pathways of the functional genes associated with the carbon (C) and nitrogen (N) cycling to cadaveric substances such as cadaverine and putrescine remain unclear. This study explored the variation of functional genes associated with C fixation, C degradation and N cycling and their influencing factors under cadaverine, putrescine and mixed treatments. Our results showed only putrescine significantly increased the alpha diversity of C fixation genes, while reducing the alpha diversity of N cycling genes in sediment. For the C cycling, the mixed treatment significantly decreased the total abundance of reductive acetyl-CoA pathway genes (i.e., acsB and acsE) and lig gene linked to lignin degradation in water, while only significantly increasing the hydroxypropionate-hydroxybutylate cycle (i.e., accA) gene abundance in sediment. For the N cycling, mixed treatment significantly decreased the abundance of the nitrification (i.e., amoB), denitrification (i.e., nirS3) genes in water and the assimilation pathway gene (i.e., gdhA) in sediment. Environmental factors (i.e., total carbon and total nitrogen) were all negatively associated with the genes of C and N cycling. Therefore, cadaverine and putrescine exposure may inhibit the pathway in C fixation and N cycling, while promoting C degradation. These findings can offer some new insight for the management of amine pollution caused by animal cadavers. [Display omitted] [ABSTRACT FROM AUTHOR]

Cyanobacterial biofertilizers provide soil fertility and productivity gains at varying levels in paddy rice cultivation. The colonization and influences of introduced strains in different soil types with characteristic compositions of native cyanobacteria remain largely unknown. In this work, seven paddy rice soils with the composition of indigenous cyanobacteria described by amplicon sequencing analysis were inoculated with the cyanobacterial biofertilizer. The microbial abundance and the cyanophage concentrations were evaluated under light-dark or continuous dark cycles using quantitative polymerase chain reaction (qPCR) assays. The copies of cyanobacterial-16S rRNA gene markers varied from 5.65 × 106 to 9.22 × 107 g-1 soil, and their abundance increased significantly in the inoculated soils. The cyanophage concentrations, quantified using the capsid assembly protein gene g20 in the soils tested, ranged from 3.04 × 108 to 9.24× 108 g-1 soil on 30 days after incubation. There were significant increases in the abundance of the nifH gene copies, about 1.54×105 to 1.35×106 g-1, in the inoculated soils, albeit with soil type-specific responses. The gene markers of C and N cycling (i.e., cbbL and nifH, respectively), taxonomic markers (of archaea, bacteria, and cyanobacteria), and cyanophage-specific gene copies showed strong and positive correlation with the cyanobacterial biofertilizer inoculation. However, the genes related to nitrification (bacterial and archaeal amoA) and denitrification (nirS, nirK, narG, and nosZ) were clustered together in the uninoculated soils. The rice rhizospheres in three representative paddy soil types, using metatranscriptomics analysis, showed distinctive colonization by cyanobacteria, with several members yet to be described. These results indicate the potential for improving cyanobacterial biofertilizers for their contributions to plant growth and fertility gains in a soil-specific way. [ABSTRACT FROM AUTHOR]

The proto-atmosphere serves as a crucial starting point for the carbon cycle. Estimations based on atmospheric data from Mars and Venus suggest that Earth's proto-atmosphere contained >110 bar of CO2 and >2.6 bar of nitrogen. The proto-atmosphere had over 1000 bar of water vapor during the magma ocean stage, assuming the proto-ocean had a volume of two oceans of water. During this stage both water and carbon dioxide were in a supercritical state at the magma-atmosphere interface. Intense serpentinization reactions occurred due to rock-water interaction, producing abundant hydrogen. Consequently, nitrogen is reduced to ammonia, and carbon dioxide to methane, forming carbonate simultaneously. The proto-atmosphere dominated by methane, ammonia, and hydrogen formed a significant amount of amino acids through lightning. This process is essential not only to the origin of life, but also to the early carbon-nitrogen cycle on Earth. By the Hadean eon, a large amount of CO2 was sequestered as carbonate and organic material. Subsequently, it mainly entered the deep mantle through mantle overturn or subduction. In the mantle transition zone, carbonate undergoes "Redox freezing", where carbonate is reduced to diamond through oxidation of ferrous iron in the melt. In the lower mantle, Fe2+ undergoes disproportionation reactions, forming Fe3+ and metallic iron. Among these, Fe3+ mainly resides in bridgmanite, thereby increasing the oxygen fugacity of the lower mantle, while metallic iron falls to the Earth's core. The distribution of carbon in the mantle is crucial for deep carbon cycling. The density curves of diamond and mantle peridotite melt intersect at the bottom of the mantle transition zone (about 660 km). This density crossover leads to the accumulation of diamond during the magma ocean stage. When materials such as subducting slabs enter the lower mantle, compensatory upwelling of lower mantle material occurs. Bridgmanite enters the upper mantle, decomposes, releasing Fe3+ ions and oxidizes diamond to carbonate, which under thermal disturbance from kimberlite and igneous carbonatites, moves upward. This carbonate layer may have caused significant topographic fluctuations at the 660 km boundary. Currently, diamond in this layer may still not have been completely oxidized to carbonate or carbon dioxide, serving as a redox buffering layer. This is a key factor in constraining deep carbon cycling. Subduction zones are important pathways for facilitating the cycling. Processes in the Earth's deep carbon cycle significantly influence the carbon content of surface reservoirs. The fluctuations in atmospheric CO2 content since the Neogene are closely linked to the uplift of the Tibetan Plateau and the subduction of the western Pacific Plate. Around 60 million years ago, the closure of the Neo-Tethys Ocean led to subduction of the Indian passive margin. The massive sediments on the Indian margin carried down large amounts of carbonate and organic material into the mantle, and the resulting volcanism released large amounts of greenhouse gases such as CO2 and methane into the atmosphere. The subduction of the Neo-Tethys Ocean passive margin weakened at about 51 Ma, and subduction of the western Pacific began. The depth of the western Pacific Ocean generally exceeds the carbonate compensation depth, and the amount of carbonate carried by subducting oceanic crust is minimal. Consequently, the input of subducted carbonate decreased significantly, leading to a substantial reduction in CO2 emissions from volcanoes. Based on volcanic data from the past 12,000 years, the average rate of volcanic eruptions in subduction zones is estimated to be about 3 cubic kilometers per year. The weathering rate of volcanic ash is much higher than that of continental crust materials such as granite. The calcium, magnesium, and other ions provided by weathering of global volcanic ash are equivalent to the flux of global rivers into the oceans. The increase in volcanic ash and the decrease in CO2 emissions from subduction zones have led to a decrease in atmospheric CO2 levels, which is a key factor in the sustained global cooling since 51 million years ago. [ABSTRACT FROM AUTHOR]

Stemflow is a conduit for the transport of canopy-derived dissolved organic matter (DOM) to the forest floor. This study examined the character of stemflow DOM for four tree species over four phenophases (leafless, emergence, leafed, and senescence for deciduous species and leafed-winter, emergence, leafed- spring/summer, and senescence for coniferous species) occurring in temperate forests; namely, Betula lenta L. (sweet birch), Fagus grandifolia Ehrh. (American beech), Liriodendron tulipifera L. (yellow poplar), and Pinus rigida Mill. (pitch pine). American beech exhibited the lowest average specific UV absorbance at 254 nm (SUVA254) values, while yellow poplar displayed the highest values. SUVA254 values were largest in senescence and smallest in emergence. The spectral slope ratio was lower for pitch pine than the deciduous tree species. Humification index (HIX) values decreased across all species during the emergence phenophase. The developed and validated stemflow-specific four-component parallel factor analysis (PARAFAC) model demonstrated the combined influence of interspecific and temporal fluctuations on the composition of humic and protein-like substances within stemflow. By separating and examining stemflow DOM independent of throughfall, our study provides fresh insights into the spatiotemporal dynamics of stemflow inputs to near-trunk soils that may inform hot spots and hot moments theories. [ABSTRACT FROM AUTHOR]

Lake Erie's Western Basin is a eutrophic region and likely hotspot for carbon transformation. While this basin has received much attention for its high nutrient loads from the Maumee River and recurring harmful algal blooms, carbon has gone understudied. To investigate the seasonal and spatial variability in inorganic and organic carbon budgets, we completed three surveys in spring, summer, and fall on a transect from the Maumee River to South Bass Island. In each survey, we observed higher spatial variability of all carbon species within 11 km of the Maumee River mouth relative to sites outside of Maumee Bay. This variability was driven by pulses of direct river water carbon, steep nutrient gradients, and patchy bloom conditions. Seasonal variability was also greater in Maumee Bay, with the highest river discharge in June adding large amounts of dissolved inorganic and organic carbon and pCO2 flux out of the water when productivity from the diatom bloom was smaller. In August, when and where we observed a Microcystis bloom, particulate organic carbon increased in concentration, and pCO2 flux switched directions into the water. In October, Chl‐a concentrations and oxygen saturations were lowest, indicating a seasonal slowdown in productivity, and river discharge was the lowest, resulting in the lowest total carbon observed and dissolved organic matter chemistry indicating less contribution from the terrestrial watershed. In the open water outside of Maumee Bay seasonal and spatial carbon budget dynamics were more stable, highlighting the importance of riverine inputs on lake carbon cycling. Plain Language Summary: The Maumee River has a large influence on the water quality of Lake Erie's Western Basin. Past research in this region focused on the connection between nutrients, such as phosphorus and nitrogen, and harmful algal blooms. Carbon, which is a water quality indicator and can serve as a component of greenhouse gases, is less studied. The goal of this project was to quantify changes in carbon over space and time along a gradient from the Maumee River into the Western Basin. We performed research cruises in spring, summer, and fall and collected samples for dissolved inorganic carbon, dissolved organic carbon, and particulate organic carbon. We found the Maumee River influenced the carbon budget due to direct inputs of carbon as well as nutrient inputs that fueled algal blooms. In the spring and summer when the Maumee River had high flow, much of the carbon in Maumee Bay was from the river, but later in the year as flow decreased an larger percent of the carbon came from the algal bloom, which changed which kind of carbon was most common due to photosynthesis. Throughout the study the open water of the basin had less variability in carbon compared to Maumee Bay. Key Points: Carbon in the Western Basin of Lake Erie is heavily influenced by river inputSpatial and temporal variability of inorganic and organic carbon is high in Maumee BaySeasonal bloom dynamics transform carbon [ABSTRACT FROM AUTHOR]

Natural phenomena and scientific issues are intrinsically interdisciplinary. Students need to study a variety of academic disciplines in the natural sciences to explain a phenomenon or its related problems. Our goal in the current study was to examine the epistemological foundation of students' interdisciplinary understanding of carbon cycling using the supervised latent Dirichlet allocation model. The 454 students in this study were from a public high school and a public research university in Texas. The students' interdisciplinary understanding was shown in each of the constructed response items. In the relationship between the proportion of interdisciplinarity in students' answers to the constructed response items and students' scores on interdisciplinary understanding, all integrations of disciplines were statistically significant in explaining students' interdisciplinary understanding. Moreover, one particular integration set had advantages for obtaining a high score. We found that science coursework contributed to students' interdisciplinary understanding in different ways, and this interdisciplinary understanding was influenced by the number and type of science courses taken. Characterizing interdisciplinarity based on the clusters of science disciplines provided insights into how students synthesize their knowledge. The significance of this study lies in its potential impact on diverse curricular and instructional approaches in interdisciplinary science education. [ABSTRACT FROM AUTHOR]

Droughts can affect ecosystem CO2 fluxes directly or indirectly by changing plant community composition. However, it is unknown whether shifts in plant community composition buffer or amplify the response of ecosystem CO2 fluxes to droughts with different seasonal timing, as plant phenology and physiology of the different plant functional types respond differently to droughts. To identify the interaction of drought timing and plant community composition in regulating ecosystem CO2 fluxes, we conducted a three‐year manipulative experiment in which extreme droughts occurring in the early, mid and late growing seasons were separately imposed on experimental plot communities comprising graminoids, shrubs and their combination in a semi‐arid grassland of Inner Mongolia, China. Overall, mid‐season drought caused the largest negative effects regardless of plant community composition. In addition to decreasing aboveground biomass, mid‐season drought suppressed fluxes by reducing leaf photosynthetic rate, while early‐season and late‐season drought reduced fluxes mainly by shortening growing season length. All three community compositions had consistent responses to early‐season and mid‐season droughts. However, ecosystem CO2 fluxes in the combination community were less negatively affected by late‐season drought than in either shrub or graminoid communities because the growing season length was shortened less. Synthesis. Our results highlight that it is important to account for interactions of seasonal timing and plant community composition when predicting magnitude and pathways of drought effects on ecosystem carbon cycling. [ABSTRACT FROM AUTHOR]

Rhizodeposition fuels carbon (C) and nutrient cycling in soil. However, changes in the dynamics of microbial growth on rhizodeposits with increasing distance from the root is not well studied. This study investigates microbial growth on individual organic components of rhizodeposits and maize root‐derived exudates and mucilage from agricultural soil. By creating a gradient of substrate concentrations, we simulated reduced microbial access to rhizosphere C with increasing distance to the root surface. We identified distinct C‐thresholds for the activation of microbial growth, and these were significantly higher for rhizodeposits than singular, simple sugars. In addition, testing for stoichiometric constraints of microbial growth by supplementing nitrogen (N) and phosphorus (P) showed accelerated and increased microbial growth by activating a larger proportion of the microbial biomass. Early and late season exudates triggered significantly different microbial growth responses. The mineralization of early‐season exudates was induced at a high C‐threshold. In contrast, the mineralization of late‐season exudates showed 'sugar‐like' properties, with a low C‐threshold, high substrate affinity, and a reduced maximum respiration rate of microorganisms growing on the added substrate. Mucilage exhibited the highest C‐threshold for the activation of microbial growth, although with a short lag‐period and with an efficient mucilage degradation comparable to that of sugars. By determining kinetic parameters and turnover times for different root‐derived substrates, our data enable the upscaling of micro‐scale processes to the whole root system, allowing more accurate predictions of how rhizodeposition drives microbial C and nutrient dynamics in the soil. [ABSTRACT FROM AUTHOR]

The subpolar North Atlantic plays an outsized role in the atmosphere‐to‐ocean carbon sink. The central Irminger Sea is home to well‐documented deep winter convection and high phytoplankton production, which drive strong seasonal and interannual variability in regional carbon cycling. We use observational data from moored carbonate chemistry system sensors and annual turn‐around cruise samples at the Ocean Observatories Initiative's Irminger Sea Array to construct a near‐continuous time series of mixed layer total dissolved inorganic carbon (DIC), pCO2, and total alkalinity from summer 2015 to summer 2022. We use these carbonate chemistry system time series to deconvolve the physical and biological drivers of surface ocean carbon cycling in this region on seasonal, annual, and interannual time scales. We find high annual net community production within the seasonally varying mixed layer, averaging 9.8 ± 1.6 mol m−2 yr−1 with high interannual variability (range of 6.0–13.9 mol m−2 yr−1). The highest daily net community production rates occur during the late winter and early spring, prior to the observed high chlorophyll concentrations associated with the spring phytoplankton bloom. As a result, the winter and early spring play a much larger role in biological carbon export from the mixed layer than traditionally thought. Plain Language Summary: The subpolar North Atlantic takes in more carbon from the atmosphere than other areas of the ocean relative to its size. This is partially caused by photosynthesis in the surface ocean, which turns inorganic carbon into organic carbon that is transported into the deep ocean in a process known as the biological carbon pump. Using measurements from sensors on moorings in the Irminger Sea, we construct a 7‐year time series of the different parts of the inorganic carbon system. Using these, we separate out the forces that impact how much inorganic carbon has the potential to be exchanged with the atmosphere. We find that biological processes remove inorganic carbon from the surface ocean in the spring, summer, and early fall, while in the winter the surface ocean gets deeper and encompasses waters from below that have higher carbon content. The total amount of inorganic carbon removed from the surface ocean each year by biological process is extremely high in the Irminger Sea compared to other global ocean regions. This research highlights the importance of long‐term, full year measurements to understand carbon cycle dynamics. Key Points: We present the first multi‐year, near‐daily mixed layer total dissolved inorganic carbon time series in the Irminger SeaAnnual net community production within the seasonally varying mixed layer is high (9.8 ± 1.6 mol m−2 yr−1) and has large interannual variabilityThe greatest rates of inorganic carbon removal from the mixed layer via photosynthesis take place prior to mixed layer shoaling [ABSTRACT FROM AUTHOR]

Streams are important freshwater habitats in large‐scale carbon budgets because of their high CO2 fluxes which are driven by high CO2 concentrations and surface‐water turbulence. High CO2 concentrations are promoted by terrestrial carbon inputs, groundwater flow, and internal respiration, all of which vary greatly across space and time. We used environmental monitoring data to calculate CO2 concentrations along with a wide range of predictor variables including outputs from a national hydrological model and trained machine learning models to predict spatially distributed seasonal CO2 concentrations in Danish streams. We found that streams were supersaturated in dissolved CO2 (mean = 118 μM) and higher during autumn and winter than during spring and summer. The best model, a Random Forest model, scored R2 = 0.46, MAE = 46.0 μM, and ⍴ = 0.72 on a test set. The most important predictor variables were catchment slope, seasonality, height above nearest drainage, and depth to groundwater, highlighting the importance of landscape morphometry and soil‐groundwater‐stream connectivity. Stream CO2 fluxes determined from the predicted concentrations and gas transfer velocities estimated using empirical relationships averaged 253 mmol m−2 d−1, and the annual emissions were 513 Gg CO2 from the national stream network (area = 139 km2). Our analysis presents a framework for modeling seasonal CO2 concentrations and estimating fluxes at a national scale by means of large‐scale hydrological model outputs. Future efforts should consider further improving the temporal resolution, direct measurements of fluxes and gas transfer velocities, and seasonal variation in stream surface area. Plain Language Summary: Streams play an essential role in the global carbon cycle as they usually are very rich in CO2 and thus emit much CO2 to the atmosphere To estimate how much CO2 is emitted from streams, we used environmental data to calculate CO2 concentrations and a wide range of terrain and stream flow characteristics. We used this data to train a machine learning model to predict seasonal stream CO2 concentrations across Denmark. We found that CO2 concentrations in Danish streams were generally higher during autumn and winter than during spring and summer. The key factors determining CO2 concentrations included terrain slope, seasonality, elevation relative to nearby streams, and depth to groundwater. From the national stream CO2 concentrations, we estimated the exchange of CO2 between stream and atmosphere and the annual emissions. This study demonstrates how machine learning models and data from multiple sources can be used to predict stream CO2 concentrations at large scales. The framework and model allow us to quantify and manage the CO2 emissions from streams at a national scale. Key Points: Environmental monitoring data and hydrological model outputs can be used to quantify stream CO2 concentrations and fluxes at national scaleMachine learning models can be trained to predict seasonal stream CO2 concentrations based on catchment and stream characteristicsThe most important drivers of stream CO2 are related to landscape morphometry and soil‐groundwater‐stream connectivity [ABSTRACT FROM AUTHOR]

Abstract Background Thinning practices are useful measures in forest management and play an essential role in maintaining ecological stability. However, the effects of thinning on the soil properties and microbial community in large Chinese fir timber plantations remain unknown. The purpose of this study was to investigate the changes in soil physicochemical properties and microbial community composition in topsoil (0–20 cm) under six different intensities (i.e., 300 (R300), 450 (R450), 600 (R600), 750 (R750) and 900 (R900) trees per hectare and 1650 (R1650) as a control) in a large Chinese fir timber plantation. Results Compared with the CK treatment, thinning significantly altered the contents of soil organic carbon (SOC) and its fractions but not in a linear fashion; these indicators were highest in R900. In addition, thinning did not significantly affect the soil microbial community diversity indices but significantly affected the relative abundance of the core microbial community. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant bacterial phyla; the relative abundances of Proteobacteria and Acidobacteria were highest in R900, and that of Actinobacteria was lowest in R900. The dominant fungal phyla were Ascomycota, Basidiomycota and Mucoromycota; the relative abundance of Ascomycota was lowest in R900, and that of Mucoromycota was highest in R900. The fungal microbial community composition was more sensitive than the bacterial community composition. The activity of the carbon-cycling genes was not linearly correlated with thinning, and the abundance of C-cycle genes was highest in R900. Conclusions These findings are important because they show that SOC and its fractions and the abundance of the soil microorganism community in large Chinese fir timber plantations can be significantly altered by thinning, thus affecting the capacity for carbon storage. These results may advance our understanding of how the density of large timber plantations could be modified to promote soil carbon storage.

Abstract Background Photodegradation of plant litter plays a pivotal role in the global carbon (C) cycle. In temperate forest ecosystems, the exposure of plant litter to solar radiation can be significantly altered by changes in autumn phenology and snow cover due to climatic change. How this will affect litter decomposition and nutrient dynamic interacting with forest canopy structure (understorey vs. gaps) is uncertain. In the present study, we conducted a field experiment using leaf litter of early-fall deciduous Betula platyphylla (Asian white birch) and late-fall deciduous Quercus mongolica (Mongolian oak) to explore the effect of change in autumn solar radiation on dynamics of litter decomposition in a gap and understorey of a temperate mixed forest. Results Exposure to the full-spectrum of not only significantly increased the loss of mass, C, and lignin, but also modified N loss through both immobilization and mineralization during the initial decomposition during autumn canopy opening, irrespective of canopy structure and litter species. These effects were mainly driven by the blue-green spectral region of sunlight. Short-term photodegradation by autumn solar radiation had a positive legacy effect on the later decomposition particularly in the forest gap, increasing mass loss by 16% and 19% for Asian white birch and Mongolia oak, respectively. Conclusions Our results suggest that earlier autumn leaf-fall phenology and/or later snow cover due to land-use or climate change would increase the exposure of plant organic matter to solar radiation, and accelerate ecosystem processes, C and nutrient cycling in temperate forest ecosystems. The study provides a reference for predictive research on carbon cycling under the background of global climate change.

Soil metabolomics is an emerging approach for profiling diverse small molecule metabolites, i.e., metabolomes, in the soil. Soil metabolites, including fatty acids, amino acids, lipids, organic acids, sugars, and volatile organic compounds, often contain essential nutrients such as nitrogen, phosphorus, and sulfur and are directly linked to soil biogeochemical cycles driven by soil microorganisms. This paper presents an overview of methods for analyzing soil metabolites and the state-of-the-art of soil metabolomics in relation to soil nutrient cycling. We describe important applications of metabolomics in studying soil carbon cycling and sequestration, and the response of soil organic pools to changing environmental conditions. This includes using metabolomics to provide new insights into the close relationships between soil microbiome and metabolome, as well as responses of soil metabolome to plant and environmental stresses such as soil contamination. We also highlight the advantage of using soil metabolomics to study the biogeochemical cycles of elements and suggest that future research needs to better understand factors driving soil function and health.

Source‐to‐sink transfer of sediment and organic carbon (OC) is regulated by river mobility. Quantifying trends in river mobility is, however, challenging due to diverse planform morphologies (e.g., meandering, braided) and measurement methods. Here, we utilize a remote‐sensing method applicable to all planform morphologies to quantify the mobility timescales of 80 rivers worldwide. Results show that, across the continuum from meandering to braided rivers, there is a systematic reduction in the timescales of channel mobility and—to a lesser extent—floodplain reworking. This leads to a decrease in the efficiency with which braided rivers rework old floodplain material compared to their meandering counterparts. Reduced floodplain reworking efficiency of braided rivers leads to smaller channel‐belt areas relative to their size. Results suggest that river‐mobility timescales derived from remote sensing can aid in the characterization of sediment and OC storage and transit times at a global scale. Plain Language Summary: Rivers transport sediment and organic carbon (OC) from the mountains to the sea, and river movement affects sediment and OC transit times in landscapes. Understanding the controls on timescales of river movement is critical for assessing how fluvial processes influence the terrestrial carbon cycle. While previous work has quantified different river planform shapes on the Earth's surface (e.g., meandering, wandering, and braided), little is known about how the pace and nature of river movement is different between river planform shapes. This is because we lack methods to measure and compare river movement across different river planform shapes. Here, we leverage a tool to quantify river movement from time series of satellite imagery that is equally applicable to all river planform shapes. We apply this method to calculate the timescales of river movement of 80 rivers worldwide for the last 37 years. We show that (a) braided rivers migrate faster than meandering rivers, and (b) braided rivers move over a smaller area relative to their size. Comparing results with geochemical observations from the Río Bermejo—a well‐studied river for sediment‐OC cycling—we show that our mobility framework may provide a new way to assess sediment and OC storage timescales in floodplains. Key Points: We quantify timescales of floodplain reworking and channel‐overlap decay from satellite imagery of 80 rivers worldwideFrom meandering to braided planform morphology, there is a reduction in the overlap timescale and the reworking timescaleMobility timescales provide a means for remotely quantifying terrestrial‐sediment and organic‐carbon storage and transit [ABSTRACT FROM AUTHOR]

Background: Photodegradation of plant litter plays a pivotal role in the global carbon (C) cycle. In temperate forest ecosystems, the exposure of plant litter to solar radiation can be significantly altered by changes in autumn phenology and snow cover due to climatic change. How this will affect litter decomposition and nutrient dynamic interacting with forest canopy structure (understorey vs. gaps) is uncertain. In the present study, we conducted a field experiment using leaf litter of early-fall deciduous Betula platyphylla (Asian white birch) and late-fall deciduous Quercus mongolica (Mongolian oak) to explore the effect of change in autumn solar radiation on dynamics of litter decomposition in a gap and understorey of a temperate mixed forest. Results: Exposure to the full-spectrum of not only significantly increased the loss of mass, C, and lignin, but also modified N loss through both immobilization and mineralization during the initial decomposition during autumn canopy opening, irrespective of canopy structure and litter species. These effects were mainly driven by the blue-green spectral region of sunlight. Short-term photodegradation by autumn solar radiation had a positive legacy effect on the later decomposition particularly in the forest gap, increasing mass loss by 16% and 19% for Asian white birch and Mongolia oak, respectively. Conclusions: Our results suggest that earlier autumn leaf-fall phenology and/or later snow cover due to land-use or climate change would increase the exposure of plant organic matter to solar radiation, and accelerate ecosystem processes, C and nutrient cycling in temperate forest ecosystems. The study provides a reference for predictive research on carbon cycling under the background of global climate change. [ABSTRACT FROM AUTHOR]

The complex interactions among soil, vegetation, and site hydrologic conditions driven by precipitation and tidal cycles control the biogeochemical transformations and bi‐directional exchange of carbon and nutrients across the terrestrial–aquatic interfaces (TAIs) in coastal regions. This study uses a highly mechanistic model, Advanced Terrestrial Simulator (ATS)‐PFLOTRAN, to explore how these interactions affect exchanges of materials and carbon and nitrogen cycling. We used a transect in the Chesapeake Bay region that spans zones of open water, coastal wetland, transition, and upland forest. We designed several simulation scenarios to parse the effects of the individual controlling factors and the sensitivity of carbon cycling to reaction rate parameters derived from laboratory experiments. Our simulations reveal an active zone for carbon cycling under the transition zones between the wetland and the upland. Evapotranspiration is found to enhance the exchange fluxes between the surface and subsurface domains, resulting in a higher dissolved oxygen concentration in the TAIs. The transport of organic carbon derived from plant leaves and roots provide an additional source of organic carbon needed for the aerobic respiration and denitrification processes in the TAIs. The variability in reaction rate parameters associated with microbial activities is also found to play a dominant role in controlling the heterogeneity and dynamics of the simulated redox conditions. This modeling‐focused exploratory study enabled us to better understand the complex interactions among soil, water and microbes that govern the hydro‐biogeochemical processes at the TAIs, which is an important step toward representing coastal ecosystems in larger‐scale Earth system models. Plain Language Summary: The hydrological environment of vegetated coastal ecosystems is directly influenced by precipitation and seawater flooding, which mediates biogeochemical processes within these areas. However, the specific effects of dynamic precipitation and flooding on oxidation‐reduction conditions in these complex terrestrial‐aquatic interfaces (TAIs) are poorly understood, especially when considering the ecological processes of above‐ground plants. To address this gap, this study used integrated process‐based models, the Advanced Terrestrial Simulator (ATS) and PFLOTRAN, to examine the effects of hydrological and ecological controls on biogeochemical reactions and exchange fluxes across a TAIs transect spanning from a coastal upland forest and salt marsh to the open seawater. Our numerical experiments showed that the mixing of different waters within the TAIs significantly influenced the spatial and temporal variability in exchange fluxes across this interface along with the spatial extent of oxic subsurface zones. The interface between the oxic and anoxic zones shifts in response to periodic fluctuations in tidal elevations as higher tides drive more oxygenated water toward the TAIs. Meanwhile, vegetation evapotranspiration removes more water from the subsurface during warm summer months, leading to larger exchange fluxes across the TAIs. Reaction rate parameters that depend on the interactions between the soil and microbes have a large effect on carbon and oxygen consumption represented in our models. A higher aerobic respiration rate results in larger hypoxic and anoxic zones because the dissolved oxygen is consumed more quickly. Our modeling‐based study provided insights into the mechanisms that control the exchange fluxes and cycling of carbon and nitrogen at coastal TAIs, which can be used to inform potential management strategies for mitigating the impacts of climate change on these ecosystems. Key Points: Tidal elevations, precipitation, and evapotranspiration (ET) interact to control dynamic exchange fluxes across the coastal terrestrial aquatic interfaceIntegrated hydrobiogeochemical modeling reveals variability in redox conditions along gradient of upland, transition, and wetland to oceanThe high uncertainty in microbial‐remediated aerobic respiration rate has significant impact on modeling carbon cycling in coastal regions [ABSTRACT FROM AUTHOR]

Grasslands are among the most widespread environments on Earth, yet we still have poor knowledge of their microbial-mediated carbon cycling in the context of human activity and climate change. We conducted a systematic bibliometric analysis of 1,660 literature focusing on microbial-mediated grassland carbon cycling in the Scopus database from 1990 to 2022. We observed a steep increase in the number of multidisciplinary and interdisciplinary studies since the 2000s, with focus areas on the top 10 subject categories, especially in Agricultural and Biological Sciences. Additionally, the USA, Australia, Germany, the United Kingdom, China, and Austria exhibited high levels of productivity. We revealed that the eight papers have been pivotal in shaping future research in this field, and the main research topics concentrate on microbial respiration, interaction relationships, microbial biomass carbon, methane oxidation, and high-throughput sequencing. We further highlight that the new research hotspots in microbial-mediated grassland carbon cycling are mainly focused on the keywords "carbon use efficiency," "enzyme activity," "microbial community," and "high throughput sequencing." Our bibliometric analysis in the past three decades has provided insights into a multidisciplinary and evolving field of microbial-mediated grassland carbon cycling, not merely summarizing the literature but also critically identifying research hotspots and trends, the intellectual base, and interconnections within the existing body of collective knowledge and signposting the path for future research directions. [ABSTRACT FROM AUTHOR]

Any scientific career is a mix of planning and stochastic events, often with a fair share of the latter. I illustrate this by the evolution of my own career. Ecosystem studies of food webs under the impact of eutrophication (Master), and carbon cycling in DOC (Dissolved Organic Carbon)-rich lakes (PhD) led me to elemental ratios in organisms and the establishment of ecological stoichiometry. The role of phosphorus (P) in cellular processes again led to research on the evolution and regulation of genome size. As climate came higher on the agenda, it was time to apply the basic research on the C-cycle and climate in a wider context. As natural scientists, we should also engage in even wider contexts, and I have enjoyed discussions and co-operation with philosophers, psychologist, and social scientists. This helps seeing our own work in context. We should also reflect on why we do science. I have always felt that science should also add purpose to life by giving something back to society, and I have devoted much time to outreach, public talks, debates, and writing popular science books. It takes some time, but it is also rewarding and important—perhaps even more so than yet another paper. [ABSTRACT FROM AUTHOR]

Summary: Deserts represent key carbon reservoirs, yet as these systems are threatened this has implications for biodiversity and climate change. This review focuses on how these changes affect desert ecosystems, particularly plant root systems and their impact on carbon and mineral nutrient stocks. Desert plants have diverse root architectures shaped by water acquisition strategies, affecting plant biomass and overall carbon and nutrient stocks. Climate change can disrupt desert plant communities, with droughts impacting both shallow and deep‐rooted plants as groundwater levels fluctuate. Vegetation management practices, like grazing, significantly influence plant communities, soil composition, root microorganisms, biomass, and nutrient stocks. Shallow‐rooted plants are particularly susceptible to climate change and human interference. To safeguard desert ecosystems, understanding root architecture and deep soil layers is crucial. Implementing strategic management practices such as reducing grazing pressure, maintaining moderate harvesting levels, and adopting moderate fertilization can help preserve plant–soil systems. Employing socio‐ecological approaches for community restoration enhances carbon and nutrient retention, limits desert expansion, and reduces CO2 emissions. This review underscores the importance of investigating belowground plant processes and their role in shaping desert landscapes, emphasizing the urgent need for a comprehensive understanding of desert ecosystems. [ABSTRACT FROM AUTHOR]

Background: We are facing the challenge of sustainable phosphorus (P) use due to high P inputs in farmland and low P-use efficiency of crops, which leads to critical soil P imbalances and accelerates consumption of limited P resources. Organic P is an essential component of the soil P cycle, and if managed properly, may compensate partly for decreased usage of P fertilizers. However, organic P dynamics in the rhizosphere has received little attention even though it is important for P availability to plants. Scope: We review biological turnover of organic P in soils, focusing on the processes driven by roots and microbial communities and their interactions in the rhizosphere. We also consider recent progress in understanding of organic P acquisition strategies that integrate soil carbon (C) cycling. We address several perspectives to achieve more sustainable P use in agriculture via rhizosphere management aimed at recycling and re-using soil organic P. Conclusions: Organic P mineralization by microorganisms may be limited by low P and/or C availability. In these processes, plants interact with microorganisms to alter stoichiometric ratios of C to P in the rhizosphere soils or microbial community, thus impacting on turnover of organic P into inorganic P for plant absorption, which is manifested in plant-microbial facilitation/competition in the rhizosphere. We highlight future research in improving rhizosphere management of agroecosystems by optimizing nutrient inputs and enhancing rhizosphere interactions to manipulate P and C dynamics towards sustainable organic P use. [ABSTRACT FROM AUTHOR]

Phytoplankton stoichiometry modulates the interaction between carbon, nitrogen and phosphorus cycles. Environmentally driven variations in phytoplankton C:N:P can alter biogeochemical cycling compared to expectations under fixed ratios. In fact, the assumption of fixed C:N:P has been linked to Earth System Model (ESM) biases and potential misrepresentation of responses to future change. Here we integrate key elements of the Adaptive Trait Optimization Model (ATOM) for phytoplankton stoichiometry with the Carbon, Ocean Biogeochemistry and Lower Trophics (COBALT) ocean biogeochemical model. Within a series of global ocean‐ice‐ecosystem retrospective simulations, ATOM‐COBALT reproduced observations of phytoplankton N:P, and compared to static ratios, exhibited reduced phytoplankton P‐limitation, enhanced N‐fixation, and increased low‐latitude export, improving consistency with observations and highlighting the biogeochemical implications of dynamic N:P. We applied ATOM‐COBALT to explore the impacts of different physiological mechanisms hypothesized to underlie N:P variation, finding that two mechanisms together drove the observed patterns: proportionality of P‐rich ribosomes in phytoplankton cells to growth rates and reductions in P‐storage during scarcity. A third mechanism which linked temperature with phytoplankton biomass allocations to non‐ribosomal proteins, led only to relatively modest impacts because this mechanism decreased the temperature dependence of phytoplankton growth rates, compensating for changes in N:P. We find that there are quantitative response differences that associate distinctive biogeochemical footprints with each mechanism, which are most apparent in highly productive low‐latitude regions. These results suggest that variable phytoplankton N:P makes phytoplankton productivity and export resilient to environmental changes, and support further research on the physiological and environmental drivers of phytoplankton stoichiometry and biogeochemical role. Plain Language Summary: Marine phytoplankton are single‐celled photosynthetic organisms that live near the ocean's surface, where they absorb carbon dioxide and other nutrients. This exerts a large influence on ocean chemistry and, through the ocean's capacity to absorb carbon dioxide from the atmosphere, the Earth's climate. We explored how phytoplankton vary their requirements for two essential nutrients, nitrogen and phosphorus, based on environmental conditions, and how that variation affects the export of carbon from the surface ocean to depth. We found that flexibility in phytoplankton nutrient uptake ratios makes them use phosphorus more efficiently, driving an increase in carbon export. It also stimulates nitrogen fixation, causing an increase in nitrogen available to phytoplankton. As a result, our simulations predicted significantly less phosphorus limitation and more export from low‐latitude parts of the ocean, increasing agreement with observations. Flexible phytoplankton nutrient requirements change how marine ecosystems respond to the environment, and understanding how these nutrient requirements vary is key to predicting how the ocean will respond to future changes. Key Points: Implemented a trait‐based model of dynamic phytoplankton elemental stoichiometry within global biogeochemical simulationsDynamic stoichiometry decreased phytoplankton P‐limitation in the tropics and subtropics and increased N‐fixation and exportFrugal P‐utilization in low P environments and increased P‐rich ribosomes at high growth rates leave distinct biogeochemical fingerprints [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) is a critical player in the global carbon cycle and a common paleoclimate archive, yet the mechanisms governing its evolution, particularly in subsoil (>30 cm) systems, remain less well understood. To better characterize subsoil SOM dynamics, we investigated the isotopic compositions of SOM in fine (<2 μm) and coarser (>2 μm) grain‐size fractions of the top 2 m of a soil profile developing in eolian sediments on the Chinese Loess Plateau. We found that in the subsoil, SOM in the fine fraction, characterized by lower C/N and higher δ13C, exhibits consistently younger radiocarbon ages than those in the coarser fraction. Such offsets suggest that organo‐mineral interactions facilitate fresh carbon input to the fine fraction rather than preventing SOM decomposition. We then developed a mass‐balance model to interpret the radiocarbon data. The results suggest continual carbon input from the above‐ground biosphere to the 2‐m deep subsoil. The active subsoil organic carbon cycling can lead to significant variations in δ13CSOM under an environment that experienced substantial vegetation changes, resulting in time‐averaged signals when using δ13CSOM for paleoenvironmental reconstructions. Our study underscores the dynamic nature of the subsoil carbon pool, emphasizing its potentially underestimated role in the contemporary carbon cycle. Plain Language Summary: Soil organic carbon (SOC) plays a key role in the global carbon cycle and serves as an important material for studying past climates. However, the processes involved in its breakdown, transformation, and interaction with soil minerals, especially in deep soils, are not fully understood. To gain better understanding of the vertical movement of SOC within soils, we analyzed the radiocarbon activities of SOC in different particle‐size fractions from a 2‐m deep soil profile located on the Chinese Loess Plateau. Based on the radiocarbon data and a mass balance model, our results suggest that the deep soils (30–200 cm) receive significant and continuous input of fresh carbon from the soil surface, which then closely interact with fine‐grained minerals and microorganisms. The transport of biospheric carbon into deep soils highlight an active subsoil SOC pool in the modern carbon cycle. On the other hand, the constantly evolving SOC might modify its original geochemical signals, posing challenges for reconstructing past climates from these soil records. Key Points: Soil organic carbon in a 2‐m soil profile was systematically analyzedSubsoil organic matter is dominated by mineral‐associated microbial productsBiospheric carbon continually fuels the subsoil organic carbon pool [ABSTRACT FROM AUTHOR]

The addition of fresh substrates can alter the decomposition of the native soil organic matter, referred to as the priming effect (PE). It is a crucial process within the cycling of soil organic carbon (C) and believed to be regulated by nitrogen (N) input. However, the direction and magnitude of this N effect on the PE are complex due to the involvement of various factors following N addition into the soil. This review synthesizes the key factors driving the responses of the PE to N addition from the perspective of C-substrate quantity and quality, N addition rates and forms, soil properties including organic C stability, N availability, electrical conductivity, pH and pH buffer capacity. The temporal change in the N effect on the PE is also discussed. In studies observing a suppressive effect of N addition on the PE, the role of N addition in directly suppressing microbial community metabolism (e.g., osmotic stress and low pH) has been largely ignored. We propose the application of multi-omics techniques to examine the relationship between microbial functional traits and soil C cycling through the PE and its response to N addition, as well as the application of spatial omics and imaging techniques in exploring the connection between in-situ soil C distribution and the PE and its response to N addition. Such studies can potentially elucidate how elevated atmospheric CO2 may affect the PE and thus soil C stock via increasing plant C input and regulating nutrients sources for plant uptake under N inputs. [ABSTRACT FROM AUTHOR]

Understanding how cool-season C3 and warm-season C4 grasses will respond to climate change is critical for predicting future ecosystem functioning in many grasslands. With warming, C4 grasses are expected to increase relative to C3 grasses, but alterations in the seasonal availability of water may also influence C3/C4 dynamics because of their distinct seasons of growth. To better understand how shifts in the seasonal availability of water can affect ecosystem function in a northern mixed-grass prairie in southeastern Wyoming, we reduced early season rainfall (April–June) using rainout shelters and added the amount of excluded precipitation later in the growing season (July–September), effectively shifting spring rainfall to summer rainfall. As expected, this shift in precipitation seasonality altered patterns of soil water availability, leading to a 29% increase in soil respiration and sustained canopy greenness throughout the growing season. Despite these responses, there were no significant differences in C3 aboveground net primary production (ANPP) between the seasonally shifted treatment and the plots that received ambient precipitation, likely due to the high levels of spring soil moisture present before rainout shelters were deployed that sustained C3 grass growth. However, in plots with high C4 grass cover, C4 ANPP increased significantly in response to increased summer rainfall. Overall, we provide the first experimental evidence that shifts in the seasonality of precipitation, with no change in temperature, will differentially impact C3 versus C4 species, altering the dynamics of carbon cycling in this geographically extensive semi-arid grassland. [ABSTRACT FROM AUTHOR]

Benthic cyanobacterial mats are increasing in abundance worldwide with the potential to degrade ecosystem structure and function. Understanding mat community dynamics is thus critical for predicting mat growth and proliferation and for mitigating any associated negative effects. Carbon, nitrogen, and sulfur cycling are the predominant forms of nutrient cycling discussed within the literature, while metabolic cooperation and viral interactions are understudied. Although many forms of nutrient cycling in mats have been assessed, the links between niche dynamics, microbial interactions, and nutrient cycling are not well described. Here, we present an updated review on how nutrient cycling and microbial community interactions in mats are structured by resource partitioning via spatial and temporal heterogeneity and succession. We assess community interactions and nutrient cycling at both intramat and metacommunity scales. Additionally, we present ideas and recommendations for research in this area, highlighting top‐down control, boundary layers, and metabolic cooperation as important future directions. [ABSTRACT FROM AUTHOR]

Successional, second-growth forests dominate much of eastern North America; thus, patterns of biomass accumulation in standing trees and downed wood are of great interest for forest management and carbon accounting. The timing and magnitude of biomass accumulation in later stages of forest development are not fully understood. We applied a "chronosequence with resampling" approach to characterize live and dead biomass accumulation in 16 northern hardwood stands in the White Mountains of New Hampshire. Live aboveground biomass increased rapidly and leveled off at about 350 Mg/ha by 145 years. Downed wood biomass fluctuated between 10 and 35 Mg/ha depending on disturbances. The species composition of downed wood varied predictably with overstory succession, and total mass of downed wood increased with stand age and the concomitant production of larger material. Fine woody debris peaked at 30–50 years during the self-thinning of early successional species, notably pin cherry. Our data support a model of northern hardwood forest development wherein live tree biomass accumulates asymptotically and begins to level off at ∼140–150 years. Still, 145-year-old second-growth stands differed from old-growth forests in their live (p = 0.09) and downed tree diameter distributions (p = 0.06). These patterns of forest biomass accumulation would be difficult to detect without a time series of repeated measurements of stands of different ages. [ABSTRACT FROM AUTHOR]

The rewetting of long-term drained peatlands leads to the development of eutrophic shallow lakes, gradually inhabited by reed communities. These shallow lakes are characterized by significant nutrient and methane emissions. To comprehend the fate of organic compounds from decaying Phragmites australis litter in water and anaerobic soil layers, we conducted a 1.6-year decomposition experiment. The experiment employed bulk and lignin-derived phenol analysis, as well as Fourier-transform infrared spectroscopy. As anticipated, the highest level of decomposition was observed in the surface water body of the shallow lake, while the non-rooted degraded peat exhibited the lowest decay. The bulk mass loss of plant litter decreased with depth from 55 to 27% across the four decomposition environments. Analysis using infrared spectroscopy indicated that the decrease in mass loss was primarily driven by the breakdown of carbohydrates, which constitute a significant portion of plant litter. Interestingly, litter in the rooted degraded peat layer exhibited the highest degree of lignin decay. Furthermore, the study revealed a preferential loss of vanillin phenols and an accumulation of p-hydroxyl phenols. These findings suggest that the increased methane emissions in rewetted fens may be partially attributed to the demethoxylation of vanillin phenols and the subsequent formation of p-hydroxyl phenols. In conclusion, this study provides valuable insights into anaerobic lignin decomposition of plant litter and sheds light on potential mechanisms underlying elevated methane emissions in rewetted peatlands. Furthermore, the study's findings hold significant implications for both carbon cycling and sequestration within these ecosystems, thereby stimulating further research into the microbial community and its extended effects. [ABSTRACT FROM AUTHOR]

Estuaries are impacted by catchment land use changes, driving degradation associated with eutrophication and alterations in sediment dynamics. Estuarine ecological monitoring has typically covered only recent periods, so magnitudes and trajectories of degradation are often poorly described. Here, we develop a multi-method approach to hindcast historic estuary condition. We determined geochemical properties in dated sediment cores from two sites in the eutrophic New River Estuary (NRE), Aotearoa New Zealand. Mud, organic matter, carbon, and nitrogen (N) contents increased from ~1847 to 2019 (~20 to 100%, ~1 to ~7%, ~0.2 to ~3%, and ~0.03 to ~0.37% respectively). Historic land use modelling shows increasing catchment loads and water column total N rising from 165 to 663 mg m-3, with more rapid change in the late 20th and early 21st centuries. Strong correlations (R² = 0.93-0.95) were found between sediment N content and water column N concentrations. Trophic indicators hindcasted by a Bayesian Belief Network worsened from the mid-20th to 21st centuries. This degradation is associated with increased sheep, beef and dairy farming in the catchment. Our approach identifies nutrient and sediment loadings associated with 'tipping points' for indicators and can inform policy by identification of hazardous levels of contaminant loading for other estuaries. [ABSTRACT FROM AUTHOR]

Warming and precipitation are key global change factors driving soil carbon (C) dynamics in terrestrial ecosystems. However, the effects of warming and altered precipitation on soil microbial diversity and functional genes involved in soil C cycling remain largely unknown. We investigated the effects of warming and increased precipitation on soil C cycling in a temperate desert steppe of Inner Mongolia using metagenomic sequencing. We found that warming reduced plant richness, Shannon–Wiener and Simpson index. In contrast, increased precipitation significantly influenced Shannon–Wiener and Simpson index. Warming reduced soil microbial species by 5.4% while increased precipitation and warming combined with increased precipitation led to increases in soil microbial species by 23.3% and 2.7%, respectively. The relative abundance of Proteobacteria, which involve C cycling genes, was significantly increased by warming and increased precipitation. Warming significantly reduced the abundance of GAPDH (Calvin cycle) and celF (cellulose degradation) while it enhanced the abundance of glxR (lignin degradation). Increased precipitation significantly enhanced the abundance of pgk (Calvin cycle), coxL (carbon monoxide oxidation), malZ (starch degradation), and mttB (methane production). Moreover, a wide range of correlations among soil properties and C cycling functional genes was detected, suggesting the synergistic and/or antagonistic relationships under scenario of global change. These results may suggest that warming is beneficial to soil C storage while increased precipitation negatively affects soil C sequestration. These findings provide a new perspective for understanding the response of microbial communities to warming and increased precipitation in the temperate desert steppe. [ABSTRACT FROM AUTHOR]

Biotic factors that influence the temporal stability of microbial community functioning are an emerging research focus for the control of natural and engineered systems. The discovery of common features within community ensembles that differ in functional stability over time is a starting point to explore biotic factors. We serially propagated a suite of soil microbial communities through five generations of 28-day microcosm incubations to examine microbial community compositional and functional stability during plant litter decomposition. Using dissolved organic carbon (DOC) abundance as a target function, we hypothesized that microbial diversity, compositional stability, and associated changes in interactions would explain the relative stability of the ecosystem function between generations. Communities with initially high DOC abundance tended to converge towards a low DOC phenotype within two generations, but across all microcosms, functional stability between generations was highly variable. By splitting communities into two cohorts based on their relative DOC functional stability, we found that compositional shifts, diversity, and interaction network complexity were associated with the stability of DOC abundance between generations. Further, our results showed that legacy effects were important in determining compositional and functional outcomes, and we identified taxa associated with high DOC abundance. In the context of litter decomposition, achieving functionally stable communities is required to utilize soil microbiomes to increase DOC abundance and long-term terrestrial DOC sequestration as one solution to reduce atmospheric carbon dioxide concentrations. Identifying factors that stabilize function for a community of interest may improve the success of microbiome engineering applications. IMPORTANCE Microbial community functioning can be highly dynamic over time. Identifying and understanding biotic factors that control functional stability is of significant interest for natural and engineered communities alike. Using plant litter-decomposing communities as a model system, this study examined the stability of ecosystem function over time following repeated community transfers. By identifying microbial community features that are associated with stable ecosystem functions, microbial communities can be manipulated in ways that promote the consistency and reliability of the desired function, improving outcomes and increasing the utility of microorganisms.

Labyrinthulomycetes are a group of ubiquitous and diverse unicellular Stramenopiles and have long been known for their vital role in ocean carbon cycling. However, their ecological function from the perspective of organic matter degradation remains poorly understood. This study reports high-quality genomes of two newly isolated Labyrinthulomycetes strains, namely, Botryochytrium sp. strain S-28 and Oblongichytrium sp. strain S-429, and provides molecular analysis of their ecological functions using comparative genomics and a biochemical assay. Our results suggest that Labyrinthulomycetes may occupy multiple ecological niches in marine ecosystems because of the significant differences in gene function among different genera. Certain strains could degrade wheat bran independently by secreting cellulase. The key glycoside hydrolase families (GH1, GH5, and GH9) related to cellulase and the functional domains of carbohydrate-active enzymes (CAZymes) were more enriched in their genomes. This group can actively participate in marine biochemical cycles as decomposers. In contrast, other strains that could not produce cellulase may thrive as "leftover scavengers" and act as a source of nutrients to the higher-trophic-level plankton. In addition, our findings emphasize the dual roles of endoglucanase, acting as both exo- and endoglucanases, in the process of cellulose degradation. Using genomic, biochemical, and phylogenetic analyses, our study provides a broader insight into the nutritional patterns and ecological functions of Labyrinthulomycetes. IMPORTANCE Unicellular heterotrophic eukaryotes are an important component of marine ecosystems. However, their ecological functions and modes of nutrition remain largely unknown. Our current understanding of marine microbial ecology is incomplete without integrating these heterotrophic microeukaryotes into the food web models. This study focuses on the unicellular fungus-like protists Labyrinthulomycetes and provides two high-quality genomes of cellulase-producing Labyrinthulomycetes. Our study uncovers the basis of their cellulase production by deciphering the results of genomic, biochemical, and phylogenetic analyses. This study instigates a further investigation of the molecular mechanism of organic matter utilization by Labyrinthulomycetes in the world's oceans.

UNLABELLED: Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approaches for quantifying wetland C pools and fluxes. We first define each of the major C pools and fluxes and provide rationale for their importance to wetland C dynamics. For each approach, we clarify what component of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such as where and when an approach is typically used, who can conduct the measurements (expertise, training requirements), and how approaches are conducted, including considerations on equipment complexity and costs. Finally, we review key covariates and ancillary measurements that enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13157-023-01722-2.

The weathering of shale exerts an important control on the hydrochemical fluxes to river systems, thus influencing the global carbon, nutrient, and geochemical cycles. However, the quantitative understanding of shale weathering and its impact on global biogeochemical cycles remains inadequate due to the complex interplay between hydrological, biogeochemical, and physical processes. In this study, we develop a novel modeling approach to quantitatively interpret the long-term chemical weathering of shale occurring since the last glaciation period (15,000 years) leading to the present geochemical conditions. The model explicitly considers processes occurring across multiple phases and involved in the weathering, including: (i) the infiltration of meteoric water, (ii) the interactions between the water and the mineral assemblage via dissolution/precipitation reactions, (iii) the microbially-mediated oxidation of organic matter, (iv) the evolution of porosity induced by mineral reactions, and (v) the exchange of gases between the subsurface and the atmosphere. To implement and test our model, we conduct this study at a well-instrumented hillslope underlain by Mancos Shale and located at the East River study site, Western Colorado. Consistent with field observations, the model successfully reproduces the stratified weathering front, the complex spatial distribution of organic carbon, and the gaseous emissions of carbon dioxide from the subsurface. Model simulations show that aerobic respiration exerts a fundamental control on the weathering of shale. While previous studies have highlighted the diffusion of oxygen from the atmosphere as the primary mechanism for shale weathering, our model simulations demonstrate that aerobic respiration limits the propagation of oxygen in the shallow subsurface, and thereby inhibits the dissolution of pyrite at depth. Aerobic respiration is particularly favored in the top soil horizon due to the constant flux of oxygen from the atmosphere, the replenishment of fresh litter/plant-derived organic matter, and to a lesser extent the presence of fossil shale-associated organic matter. The acidic pore water generated through aerobic respiration within the shallow subsurface is transported to greater depths, where it sustains the dissolution of carbonate (dolomite in this example). Overall, our results demonstrate that the evolution of pyrite and carbonate depletion fronts are significantly different, and primarily depend on the ability of microorganisms to carry out microbial respiration and the various transport pathways of reactants controlling the mineral reactions under partially saturated conditions.

Organic sources are vital for crop nutrient management, but nutrient release from organic manure depends on temperature and other factors. We conducted a laboratory incubation study to investigate how temperature (15, 25, 35°C) affects the decomposition of common organic manure, which has not yet been explored in Bangladesh. The organic manures used in this study are poultry manure (PM), vermicompost (VC), bio-slurry (BS), cow dung (CD), water hyacinth compost (WHC) and rice straw compost (RSC), which were compared with a control treatment (only soil). Carbon mineralisation and CO2 emission from microbial respiration varied among organic manures and temperature regimes. The RSC- and WHC-treated soils had a higher C mineralisation than the other manures at 35°C. The mineralisation of C among the organic manures followed the order: RSC > WHC > CD > VC > BS > PM > control. Among the temperature regimes, C mineralisation followed the order 35°C > 25°C > 15°C. Manure mineralisation was associated with mineralisable C pools (carbon availability factor, Caf), and 16.4–36.5% organic C was released. Irrespective of temperature regimes, the highest easily mineralisable Caf was recorded in PM-amended soil, followed by VC-amended soil. RSC had the lowest Caf under all temperature regimes. The Caf values of all incubated manures were higher under a 35°C temperature regime. Compost preparation from organic manure and its utilisation as an integrated nutrient management component can play essential roles in mitigating climate change, reducing environmental degradation, and building more sustainable and resilient agrifood systems.

Abstract The aquatic networks that connect soils with oceans receive each year 5.1 Pg of terrestrial carbon to transport, bury and process. Stagnant sections of aquatic networks often become anoxic. Mineral surfaces attract specific components of organic carbon, which are released under anoxic conditions to the pool of dissolved organic matter (DOM). The impact of the anoxic release on DOM molecular composition and reactivity in inland waters is unknown. Here, we report concurrent release of iron and DOM in anoxic bottom waters of northern lakes, removing DOM from the protection of iron oxides and remobilizing previously buried carbon to the water column. The deprotected DOM appears to be highly reactive, terrestrially derived and molecularly distinct, generating an ambient DOM pool that relieves energetic constraints that are often assumed to limit carbon turnover in anoxic waters. The Fe-to-C stoichiometry during anoxic mobilization differs from that after oxic precipitation, suggesting that up to 21% of buried OM escapes a lake-internal release-precipitation cycle, and can instead be exported downstream. Although anoxic habitats are transient and comprise relatively small volumes of water on the landscape scale, our results show that they may play a major role in structuring the reactivity and molecular composition of DOM transiting through aquatic networks and reaching the oceans.

Benthic macrofauna modifies carbon and nutrient retention and recycling processes in coastal habitats. However, the contribution of benthic consumers to carbon and nutrient storage and recycling shows variation over spatial scales, as the benthic community composition changes in response to differences in environmental conditions. By sampling both shallow sandy and deep muddy sediments across a land-to-sea gradient in the northern Baltic Sea, we explored if benthic community composition, stoichiometry and process rates change in response to alterations in environmental conditions and food sources. Our results show that benthic faunal biomass, C, N, and P stocks, respiration rate and secondary production increase across the land-to-sea gradient in response to higher resource quality towards the open sea. The seston δ13C indicated terrestrial runoff and δ15N sewage input at the innermost study sites, whereas more fresh marine organic matter towards the open sea boosted benthic faunal carbon storage, respiration rate, and secondary production, that is, the generation of consumer biomass, which are essential processes for carbon turnover in this coastal ecosystem. Also, biological factors such as increasing species richness and decreasing biomass dominance of the clam Macoma balthica were significant in predicting benthic faunal C, N, and P stocks and process rates, especially at sandy sites. Interestingly, despite the variation in food sources, the benthic faunal C:N:P ratios remained stable across the gradient. Our results prove that human activities in the coastal area can influence the important links between biodiversity, structure, and process rates of benthic communities by modifying the balance of available resources, therefore hampering the functioning of coastal ecosystems. [ABSTRACT FROM AUTHOR]

Relatively unmanaged interstitial areas at the residential–wildland interface can support the development of novel woody plant communities. Community assembly processes in urban areas involve interactions between spontaneous and cultivated species pools that include native, introduced (exotic/non-native) and invasive species. The potential of these communities to spread under changing climate conditions has implications for the future trajectories of forests within and beyond urban areas. We quantified woody vegetation (including trees and shrubs) in relatively unmanaged "interstitial" areas at the residential–wildland interface and in exurban reference natural areas in six metropolitan regions across the continental USA. In addition, we analyzed soil N and C cycling processes to ensure that there were no major anthropogenic differences between reference and interstitial sites such as compaction, profile disturbance or fertilization, and to explore effects of novel plant communities on soil processes. We observed marked differences in woody plant community composition between interstitial and reference sites in most metropolitan regions. These differences appeared to be driven by the expanded species pool in urban areas. There were no obvious anthropogenic effects on soils, enabling us to determine that compositional differences between interstitial and reference areas were associated with variation in soil N availability. Our observations of the formation of novel communities in interstitial spaces in six cities across a very broad range of climates, suggest that our results have relevance for how forests within and beyond urban areas are assessed and managed to provide ecosystem services and resilience that rely on native biodiversity. [ABSTRACT FROM AUTHOR]

Litter decomposition represents a major path for atmospheric carbon influx into Arctic soils, thereby controlling below‐ground carbon accumulation. Yet, little is known about how tundra litter decomposition varies with microenvironmental conditions, hindering accurate projections of tundra soil carbon dynamics with future climate change. Over 14 months, we measured landscape‐scale decomposition of two contrasting standard litter types (Green tea and Rooibos tea) in 90 plots covering gradients of micro‐climate and ‐topography, vegetation cover and traits, and soil characteristics in Western Greenland. We used the tea bag index (TBI) protocol to estimate relative variation in litter mass loss, decomposition rate (k) and stabilisation factor (S) across space, and structural equation modelling (SEM) to identify relationships among environmental factors and decomposition. Contrasting our expectations, microenvironmental factors explained little of the observed variation in both litter mass loss, as well as k and S, suggesting that the variables included in our study were not the major controls of decomposer activity in the soil across the studied tundra landscape. We use these unexpected findings of our study combined with findings from the current literature to discuss future avenues for improving our understanding of the drivers of tundra decomposition and, ultimately, carbon cycling across the warming Arctic. [ABSTRACT FROM AUTHOR]

Dissolved organic matter and its colored component, Colored Dissolved Organic Matter (CDOM), play a major role in global carbon budgets, and their fluxes provide an essential link between terrestrial and aquatic biogeochemical cycles. Satellite observations can uniquely capture the hydro‐biogeochemical connectivity of terrestrial and aquatic landscapes, across scales. Yet, accurate satellite retrievals of CDOM and dissolved organic carbon (DOC) dynamics remain challenging in urbanized estuaries and coasts. Here, we present an advanced unified algorithm for space‐based retrieval of coastal CDOM and DOC dynamics and its application in Long Island Sound—one of the world's most heavily urbanized estuaries that is becoming increasingly vulnerable to climate change stressors. A rich bio‐optical data set, encompassing a wide range of environmental conditions, was integrated into the algorithm training to retrieve DOC concentrations and CDOM spectral shape (i.e., spectral slope S275–295)—a proxy for DOC quality. The new algorithms were applied to full‐resolution satellite imagery from the Sentinel‐3 Ocean and Land Color Instrument (OLCI) after thoroughly evaluating the performance of six ocean color atmospheric correction approaches (ACOLITE, BAC, C2RCC, MUMM, l2gen, and Polymer). Evaluation of the algorithms yielded mean absolute percent differences of 28%, 12%, and 10% for aCDOM(300), S275–295, and DOC, respectively. Application of the algorithms to multi‐year satellite OLCI imagery captured, for the first time, the coupled impact of seasonal transitions, wind regimes, freshwater inputs, anthropogenic disturbances, and hydrological extremes (both intense precipitation and droughts) on DOC fluxes and CDOM quality at the ecosystem scale. Results have important implications for improved predictions of coastal biogeochemical fluxes in complex urban−estuary systems. Plain Language Summary: Accounting for more than half of the total organic carbon export from land to oceans, dissolved organic carbon (DOC) provides a critical link between terrestrial and aquatic ecosystems. Earth observations from the vantage point of space can uniquely capture the hydrological and biogeochemical connectivity of terrestrial and aquatic landscapes, across spatiotemporal scales. However, accurate satellite retrievals of DOC and its colored component (CDOM) remain challenging in urbanized estuaries impacted by anthropogenic—both air and water—pollution and transient forcings. Here, we present an advanced, generalized algorithm for space‐based retrieval of coastal CDOM and DOC dynamics across different estuarine systems. After thorough evaluation of satellite imagery and its atmospheric correction, we applied this algorithm to examine carbon dynamics in Long Island Sound—one of the world's most urbanized estuaries that is particularly vulnerable to coastal hazards and climate change. Using multi‐year satellite imagery, we were able to capture, for the first time, the coupled impact of winds, riverine discharge, human activity, and extreme events (heavy storms and intense droughts) on DOC fluxes and CDOM quality at the larger ecosystem scale. This research is important for improving our understanding of the response of complex urban ecosystems to future pressures. Key Points: High performance of unified algorithms for satellite retrieval of both dissolved organic carbon (DOC) amount and quality across complex estuaries and river plumesOcean and Land Color Instrument satellite retrievals resolve biogeochemical gradients, from the urban land−water interface to the larger ecosystem scaleRiver discharge, wind regimes, and extreme events (both extreme precipitation and droughts) modulate estuarine DOC fluxes and quality [ABSTRACT FROM AUTHOR]

Joint species distribution models (JSDM) are among the most important statistical tools in community ecology. However, existing JSDMs cannot model mutual exclusion between species. We tackle this deficiency in the context of modeling plant percentage cover data, where mutual exclusion arises from limited growing space and competition for light. We propose a hierarchical JSDM where latent Gaussian variable models describe species' niche preferences and Dirichlet‐Multinomial distribution models the observation process and competition between species. We also propose a decision theoretic model comparison and validation approach to assess the goodness of JSDMs in four different types of predictive tasks. We apply our models and methods to a case study on modeling vegetation cover in a boreal peatland. Our results show that ignoring the interspecific interactions and competition reduces models' predictive performance and leads to biased estimates for total percentage cover. Models' relative predictive performance also depends on the predictive task highlighting that model comparison and assessment should resemble the true predictive task. Our results also demonstrate that the proposed JSDM can be used to simultaneously infer interspecific correlations in niche preference as well as mutual competition for space and through that provide novel insight into ecological research. [ABSTRACT FROM AUTHOR]

Although carbonates are the primary form of carbon subducted into the mantle, their fate during recycling is debated. Here we report the first coupled high‐precision Zn and Mo isotope data for Cenozoic intraplate basalts from western China. The exceptionally high δ66Zn values (+0.39 to +0.50‰) of these lavas require involvement of recycled carbonates in the mantle source. Variable δ98Mo compositions (−0.39 to +0.27‰) are positively correlated with Mo/Ce, best interpreted as mixing between isotopically light Mo from dehydrated oceanic crust and heavy Mo from recycled carbonates, which is also supported by positive coupling between δ66Zn and δ98Mo. Modeling reveals that involvement of ≤5% carbonate‐bearing oceanic crust fully resolves the observed δ66Zn–δ98Mo mantle heterogeneity probed by intracontinental basalts. Our study demonstrates that combined δ66Zn–δ98Mo data sets for mantle‐derived magmas can track recycled surficial carbonates in Earth's interior, providing a powerful geochemical tool for deep carbon science. Plain Language Summary: Carbon is an element of life and studying its geological cycle is crucial for understanding Earth's evolution including formation of a life‐supporting atmosphere. Here we report the first combined high‐precision Zn and Mo isotope data for Cenozoic intraplate lavas from western China, showing that the basalts record ≤5% carbonate‐bearing oceanic crust components in their mantle source. Our results provide new evidence for surficial carbonates being delivered into the deep upper mantle, which adds to the debate about the deepest extent of the terrestrial carbon cycle. Key Points: First combined zinc (Zn) and molybdenum (Mo) isotope data for mantle‐derived magmas to track the fate of subducted carbonatesZn−Mo isotopic compositions of Cenozoic Tarim basalts suggest surficial carbonates being delivered into the deep upper mantleWe highlight the utility of combined Zn−Mo isotope data as a powerful tool in deep carbon science [ABSTRACT FROM AUTHOR]

Most of the geologic CO2 entering Earth's atmosphere and oceans is emitted along plate margins. While C-cycling at mid-ocean ridges and subduction zones has been studied for decades, little attention has been paid to degassing of magmatic CO2 and mineral carbonation of mantle rocks in oceanic transform faults. We studied the formation of soapstone (magnesite-talc rock) and other magnesite-bearing assemblages during mineral carbonation of mantle peridotite in the St. Paul's transform fault, equatorial Atlantic. Clumped carbonate thermometry of soapstone yields a formation (or equilibration) temperature of 147 ± 13 °C which, based on thermodynamic constraints, suggests that CO2(aq) concentrations of the hydrothermal fluid were at least an order of magnitude higher than in seawater. The association of magnesite with apatite in veins, magnesite with a d13C of -3.40 ± 0.04°, and the enrichment of CO2 in hydrothermal fluids point to magmatic degassing and melt-impregnation as the main source of CO2. Melt-rock interaction related to gas-rich alkali olivine basalt volcanism near the St. Paul's Rocks archipelago is manifested in systematic changes in peridotite compositions, notably a strong enrichment in incompatible elements with decreasing MgO/SiO2. These findings reveal a previously undocumented aspect of the geologic carbon cycle in one of the largest oceanic transform faults: Fueled by magmatism in or below the root zone of the transform fault and subsequent degassing, the fault constitutes a conduit for CO2-rich hydrothermal fluids, while carbonation of peridotite represents a vast sink for the emitted CO2. [ABSTRACT FROM AUTHOR]

The aquatic networks that connect soils with oceans receive each year 5.1 Pg of terrestrial carbon to transport, bury and process. Stagnant sections of aquatic networks often become anoxic. Mineral surfaces attract specific components of organic carbon, which are released under anoxic conditions to the pool of dissolved organic matter (DOM). The impact of the anoxic release on DOM molecular composition and reactivity in inland waters is unknown. Here, we report concurrent release of iron and DOM in anoxic bottom waters of northern lakes, removing DOM from the protection of iron oxides and remobilizing previously buried carbon to the water column. The deprotected DOM appears to be highly reactive, terrestrially derived and molecularly distinct, generating an ambient DOM pool that relieves energetic constraints that are often assumed to limit carbon turnover in anoxic waters. The Fe-to-C stoichiometry during anoxic mobilization differs from that after oxic precipitation, suggesting that up to 21% of buried OM escapes a lake-internal release-precipitation cycle, and can instead be exported downstream. Although anoxic habitats are transient and comprise relatively small volumes of water on the landscape scale, our results show that they may play a major role in structuring the reactivity and molecular composition of DOM transiting through aquatic networks and reaching the oceans. [ABSTRACT FROM AUTHOR]

Global climate change and the push to develop Natural Climate Solutions have increased urgency around the need to quantify, capture, and store carbon to reduce atmospheric concentrations of carbon dioxide—but we may be overlooking a potentially important, long‐term carbon sink.Carbon stored in large woody debris (LWD) in lakes is largely missing from local and global carbon budgets. Waterlogged LWD may remain relatively intact in cold, low‐oxygen hypolimnetic regions for decades to centuries, while LWD buried in lake‐bottom sediments may store carbon for millennia.We postulate that lacustrine LWD may be an important component of local and global carbon budgets, and modern land‐use effects (deforestation, agriculture, stream flow changes) may be reducing inputs of LWD into long‐term lacustrine carbon pools. Quantifying lacustrine LWD, particularly in large lakes, is logistically challenging, resulting in a data gap in carbon budgets.Here, we propose that new aerial and underwater technologies be employed to map and quantify littoral LWD and deposits of sunken and buried LWD to estimate carbon storage and the role of lacustrine LWD in regional and global carbon cycling. [ABSTRACT FROM AUTHOR]