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Carbonic anhydrase (CA) was considered to be an important component of carbon concentrating mechanism (CCM) of algae. It was an inducible enzyme. Environmental factors, especially dissolved inorganic carbon and pH, were known to affect CA activity. Effects of inorganic carbon (CO2 and HCO3−) and pH on CA activity of gametophytes of Saccharina japonica were evaluated in this study. Under high-CO2 condition (3% CO2), the activity of external CA (CAext) was significantly decreased (P

Herein, the effect of inorganic carbon (IC) limitation on the nitrogen removal performance of the single-stage reactor containing nitritation and anammox gel carriers was investigated. As a result of a continuous feeding test, the effluent ammonium concentration increased as the IC concentration decreased, indicating the deterioration of nitritation activity, not anammox. Furthermore, the sensitivity of IC to anammox and nitritation activity was investigated in anammox and nitritation reactors, respectively. Consequently, the relationship between the effluent IC concentration and nitritation rate was well described using the Michaelis–Menten equation. The apparent K m value of nitritation was calculated as 4.4 mg-C L−1. In anammox reactor, it was calculated as 1.7 mg-C L−1. These results revealed that the affinity of nitritation gel carriers to IC was lower than that of anammox, supporting that nitritation activity was easily deactivated by decrease in the IC concentration rather than anammox. Microbial community analysis revealed that Nitrosomonas europaea and Candidatus Jettenia asiatica were the dominant species of ammonium-oxidizing and anammox bacteria. [Display omitted] • The effect of IC on the nitrogen removal performance of SSR was investigated. • The nitrogen removal performance was decreased with decrease of IC. • The effects of IC on nitritation and anammox were determined. • The affinity to IC of nitritation gel carriers was lower than that of anammox. • Dominant species in gel carriers were Nitrosomonas europaea and Candidatus Jettenia asiatica. [ABSTRACT FROM AUTHOR]

Abstract The Everglades Stormwater Treatment Areas (STAs) are a complex of large constructed wetlands that are an integral component of the State and Federal efforts to restore the Everglades ecosystem. The overall objective of this study was to determine the accumulation rates of macro‐elements including carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and associated secondary elements including calcium (Ca), magnesium (Mg), aluminum (Al), and iron (Fe) in two Everglades STAs over their periods of operation. The study was conducted in STA‐2 with parallel flow‐ways consisting of emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) and the Western flow‐way of STA‐3/4 with EAV and SAV cells operated in series. Elemental accumulation rates were determined in the unconsolidated surficial sediments (floc) and recently accreted soil (RAS) that have accumulated on top of the antecedent soil over the 14‐ and 10‐yr periods of operation for STA‐2 and STA‐3/4, respectively. Flow‐ways with SAV were more efficient than EAV in accreting mineral matter, resulting in increased bulk density and higher accumulation rates of elements. Average C accumulation in the floc and RAS of SAV flow‐ways was 320 g·m−2·yr−1 with approximately equal proportions of inorganic and organic C, while in the EAV flow‐ways accumulation rates of C ranged from 116 to 147 g·m−2·yr−1 with mostly organic C. Phosphorus accumulation rates were approximately 2–3 times higher in SAV than in EAV flow‐ways. Differences in accumulation of elements between SAV and EAV were largest for Ca with 17–42 times more Ca in SAV than EAV systems. This suggests that in the SAV systems, possible occlusion of macro‐elements and metals during CaCO3 precipitation facilitated accretion of material with high mineral content. In EAV, biomass turnover and associated biotic processes regulated organic matter accumulation rates. The spatial accumulation patterns of P, C, and N in the EAV areas of STA‐2 and STA‐3/4 were similar to those observed in the EAV areas of the natural wetlands in Water Conservation Areas, suggesting that constructed wetland systems function similarly to natural wetlands dominated by EAV areas in retaining and storing macro‐ and secondary elements.

Norwegian fjords have been recently recognized as hot spots for carbon burial due to the large amounts of terrestrial organic matter delivered to fjord sediments, as well as the high sediment accumulation rates. Here, we present the first data on the contribution of benthic foraminiferal inorganic carbon to the sediments of three Norwegian fjords. Our study shows that calcareous foraminifera, which are among the most abundant calcifying organisms in the modern global oceans, can constitute between 15% and 33% of inorganic carbon accumulated in the sediments of the two studied southern Norwegian fjords (Raunefjorden and Hjeltefjorden). In a northern Norwegian fjord (Balsfjorden), the contribution of calcareous foraminifera to the inorganic carbon pool is smaller (<1%) than the one observed in southern fjords. We also found that the amount of foraminifera‐derived carbon is primarily dependent on the species composition of the foraminifera community. Large calcareous foraminifera species, despite a lower number of individuals, constitute, on average, 13%–29% of the inorganic carbon in the two southern Norwegian fjords, while the contribution of small, highly abundant species does not exceed 4% of the inorganic carbon pools in the sediments. Calcareous foraminifera species that are indicative of dysoxic conditions have been found to have low inorganic carbon contents per specimen compared to other analysed similar‐sized calcareous foraminifera species. This relationship most likely exists due to the thin test walls of these foraminifera species, which may facilitate gas exchange. The results of our case study suggest that the climate‐driven formation of near‐bottom low‐oxygen zones may lead to the dominance of foraminifera associated with dysoxic conditions and, in consequence, to the decrease of foraminifera‐derived inorganic carbon. However, to properly analyse the contribution of carbon from thin‐walled foraminifera to the sedimentary carbon pool, further studies analysing a broader range of these species is needed. [ABSTRACT FROM AUTHOR]

The Everglades Stormwater Treatment Areas (STAs) are a complex of large constructed wetlands that are an integral component of the State and Federal efforts to restore the Everglades ecosystem. The overall objective of this study was to determine the accumulation rates of macro‐elements including carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and associated secondary elements including calcium (Ca), magnesium (Mg), aluminum (Al), and iron (Fe) in two Everglades STAs over their periods of operation. The study was conducted in STA‐2 with parallel flow‐ways consisting of emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) and the Western flow‐way of STA‐3/4 with EAV and SAV cells operated in series. Elemental accumulation rates were determined in the unconsolidated surficial sediments (floc) and recently accreted soil (RAS) that have accumulated on top of the antecedent soil over the 14‐ and 10‐yr periods of operation for STA‐2 and STA‐3/4, respectively. Flow‐ways with SAV were more efficient than EAV in accreting mineral matter, resulting in increased bulk density and higher accumulation rates of elements. Average C accumulation in the floc and RAS of SAV flow‐ways was 320 g·m−2·yr−1 with approximately equal proportions of inorganic and organic C, while in the EAV flow‐ways accumulation rates of C ranged from 116 to 147 g·m−2·yr−1 with mostly organic C. Phosphorus accumulation rates were approximately 2–3 times higher in SAV than in EAV flow‐ways. Differences in accumulation of elements between SAV and EAV were largest for Ca with 17–42 times more Ca in SAV than EAV systems. This suggests that in the SAV systems, possible occlusion of macro‐elements and metals during CaCO3 precipitation facilitated accretion of material with high mineral content. In EAV, biomass turnover and associated biotic processes regulated organic matter accumulation rates. The spatial accumulation patterns of P, C, and N in the EAV areas of STA‐2 and STA‐3/4 were similar to those observed in the EAV areas of the natural wetlands in Water Conservation Areas, suggesting that constructed wetland systems function similarly to natural wetlands dominated by EAV areas in retaining and storing macro‐ and secondary elements. [ABSTRACT FROM AUTHOR]

Lake carbon burial is of vital significance in global carbon cycle and carbon budget, particularly in the large deepwater lakes. However, carbon burial in large deepwater lakes is hard to estimate due to the difficulty in obtaining high spatial-resolution samples. In this study, we investigated distributions of total organic carbon (TOC) and inorganic carbon (TIC), two main carbon components in lake sediments, based on dozens of surficial sedimentary samples (n = 26) covering whole Lake Qinghai, the largest saline lake in China. The results showed that the TOC content, with a range of 1.4–4.8%, was significantly higher in the lake area near the northern lakeshore where human activities are concentrated and lower in the lake areas near the Buha River mouth and the eastern lake area. In contrast, the TIC content, ranging from 1.5 to 3.8%, increased from the northwestern and southeastern lake areas toward the lake center, and mainly depended on hydro-chemical and hydraulic characteristics. The inorganic carbon burial (47.77 ± 19.73 Gg C yr−1) was approximately equal to organic carbon burial (47.50 ± 22.68 Gg C yr−1) and accounted for about 50% of the total carbon burial (95.27 ± 37.74 Gg C yr−1), suggesting that saline lakes constitute a large inorganic carbon pool in addition to an organic carbon pool. Because of saline water body type in arid and semiarid regions and alpine Qinghai–Tibet Plateau, lakes in these regions have huge inorganic carbon burial potential and important contributions to the global carbon budget.

The seasonal variability of the carbonate system in the eastern Mediterranean Sea (EMed) was investigated based on discrete total alkalinity (AT), total dissolved inorganic carbon (CT), and pH measurements collected during three cruises around Crete between June 2018 and March 2019. This study presents a detailed description of this new carbonate chemistry dataset in the eastern Mediterranean Sea. We show that the North Western Levantine Basin (NWLB) is unique in terms of range of AT variation vs. CT variation in the upper water column over an annual cycle. The reasons for this singularity of the NWLB can be explained by the interplay between strong evaporation and the concomitant consumption of CT by autotrophic processes. The high range of AT variations, combined to temperature changes, has a strong impact on the variability of the seawater pCO2 (pCO2SW). Based on Argo float data, an entire annual cycle for pCO2SW in the NWLB has been reconstructed in order to estimate the temporal sequence of the potential “source” and “sink” of atmospheric CO2. By combining this dataset with previous observations in the NWLB, this study shows a significant ocean acidification and a decrease in the oceanic surface pHT25 of −0.0024 ± 0.0004 pHT25 units.a–1. The changes in the carbonate system are driven by the increase of atmospheric CO2 but also by unexplained temporal changes in the surface AT content. If we consider that the EMed will, in the future, encounter longer, more intense and warmer summer seasons, this study proposes some perspectives on the carbonate system functioning of the “future” EMed.

Stemflow can be an important pathway for the drainage of precipitation and related solutes through tree canopies to forest soils. As stemflow must drain along bark surfaces, the effects of bark structure on stemflow chemical composition is merited. This study examines the relationship between stemflow chemistry and bark surface structure for six species of varying bark morphology (four deciduous broadleaf trees and two evergreen coniferous trees) at a montane and an urban site in Japan. Stemflow from smooth-barked species contained greater concentrations of solutes that appear to be rinsed from the stem surface (i.e., sea salt aerosols); while, rougher-barked tree species contained greater or less concentrations of solutes that appear to be leached (e.g., Ca2+) or taken-up (e.g., inorganic N) by the bark, respectively. Site-specific atmospheric environments also influenced thee bark-stemflow chemistry relationships—where the greater elemental deposition in the urban plot generally resulted in greater stemflow chemistry than observed in the lower-deposition montane plot. Our results therefore suggest that the dynamics of dry deposition wash-off by stemflow, and the exchange of dissolved solutes between stemflow and the bark surface, are influenced by the surface structure of the bark and the site’s atmospheric environment. Therefore, the interactions between bark surface structure and its surrounding atmospheric environment are important factors in the stemflow-related elemental cycling between the tree and precipitation.

Reduction in riverine freshwater supply due to climate change as well as anthropogenic activities are documented throughout the globe. How river discontinuity in upstream reaches and the subsequent reduction in freshwater influx alter inorganic and organic carbon dynamics in downstream estuaries adjacent to mangroves has been rarely reported. We investigated the dynamics of the inorganic carbon system and organic matter (OM) in two Indian estuaries near mangroves; riverine freshwater supply to the Matla Estuary was reduced and that to the Dhamra Estuary was uninterrupted. Seasonal sampling was conducted over an annual cycle. We used elemental and stable isotope signatures to delineate the sources of OM and dissolved inorganic carbon (DIC). We found that compared to the Dhamra, the reduced riverine freshwater supply to the Matla increased the marine influence in the estuary on the OM degradation pathways and decreased CO2 emissions to the atmosphere. In the Dhamra, higher seasonal variability in biogeochemical pathways, facilitated high internal carbonate buffering capacity; in contrast in the Matla, the greater marine influence increased the carbonate buffering capacity, resulting in retention of higher DIC concentrations and low CO2 emissions. Dissolved and particulate organic carbon concentrations were higher in the Dhamra than the Matla, indicating higher riverine supply of these. The present study can contribute an overlooked effect of long‐term changes in riverine freshwater supply on the carbon dynamics of mangrove‐dominated estuaries, which might help to improve the understanding of coastal carbon budgets in a changing world. Plain Language Summary: Presently, the abandonment of rivers (i.e., cut‐off from main channels) are increasing throughout the globe due to siltation and other geomorphological reasons. These changes are often caused by climate and anthropogenic changes. As a result, freshwater flows from upstream rivers to downstream estuaries and subsequently to the open ocean are decreasing in many instances. We assessed the effect of reduced riverine freshwater supply due to partial river abandonment on the inorganic and organic carbon dynamics in tropical estuaries. We comparatively studied different inorganic and organic carbon forms and air‐water CO2 flux between an unhindered estuary (Dhamra) and a partially abandoned estuary (Matla), both situated near mangrove forests. We found that Matla Estuary has lower organic carbon concentration, lower partial pressure of CO2 and lesser air‐water CO2 effluxes with retention of high dissolved inorganic carbon in the water column than those of Dhamra Estuary. Although, the organic carbon percentage in the riverbed sediment in both the estuaries was comparable, relative contribution of mangrove derived blue carbon was higher in the Matla than the Dhamra. Our findings suggest that reduced riverine freshwater supply would provide both positive and negative feedbacks to air‐water CO2 exchange and carbon storage. Key Points: Effects of riverine freshwater reduction on estuarine inorganic and organic carbon dynamics, and air‐water CO2 fluxes was assessedReduced riverine freshwater resulted in reduced organic matter, high dissolved inorganic carbon, and reduced air‐water CO2 effluxesBoth climate change and anthropogenic interventions can alter riverine freshwater flows and affect such estuarine carbon dynamics [ABSTRACT FROM AUTHOR]

The sequestration of soil inorganic carbon (SIC) especially pedogenic carbonate (PC) is one of the important pathways reducing the concentration of atmospheric carbon dioxide and thus mitigating climate change in coastal areas. Using the technology of 13 C stable isotope, we analyzed the differences in the composition and storage of SIC, and explored the key physicochemical properties influencing soil PC storage in different horizons (0-10, 11-20, 21-40, 41-60, 61-80 and 81-100 cm) from Suaeda salsa wetland (SS), Spartina alterniflora wetland (SA), young poplar plantation (YP), and mature poplar plantation (MP) in coastal area of the northern Jiangsu Province. The results showed that except for the surface (0-10 cm) soil in MP, the SIC content was higher than SOC in all soil horizons. Overall, neither the soil PC to SIC ratio nor the SIC storage were significantly different in SA and SS soils. Compared to wetland soils (0-40 cm), the soil PC to SIC ratio was reduced by 32.7% and 54.1% and the PC storage was reduced by 40.5% and 59.2%, the lithogenic carbonate (LC) storage changed little, while the SIC storage was reduced by 21.0% and 17.9%, respectively in the YP and MP soils. Compared to the YP soils (0-100 cm), both the soil PC to SIC ratio and the PC storage were significantly reduced while the LC storage was significantly increased, especially at the 41-100 cm soil horizons, meanwhile, the SIC storage was not significantly changed in the MP soils. Results of the structural equation modeling (SEM) indicated that key factors influencing soil PC storage were the ratio of PC to SIC, followed by the SOC content and bulk density. SOC could inhibit the formation of soil PC. Generally, the coastal wetlands have greater SIC storage and sequestration potential than poplar plantations, and the PC sequestration can be regulated by modulating the ratio of PC to SIC and SOC content.

Continental shelf sediments are recognized as long-term stores of globally significant quantities of carbon (C) and potentially provide an important, yet largely overlooked climate regulation service via the Earth’s C cycle. Current understanding of the spatial distribution of sedimentary C across continental shelves remains poor, inhibiting the targeted management and potential inclusion of these globally significant C stores into national C budgets. Further understanding of the spatial heterogeneity of continental shelf sediments and associated C provides a foundation to quantify the organic carbon (OC) stock and better understand the role that marine sediments play in regulating the global climate and the potential for CO2 to be released through anthropogenic disturbance of these C stores. Utilizing a spectrum of available marine data, we have created bespoke sediment maps that quantify the surficial (top 10 cm) OC stock and highlight significant spatial heterogeneity in the distribution of sediments and their associated C content across the United Kingdom’s Exclusive Economic Zone (EEZ). The surficial sediments within the UK EEZ are estimated to store 524 ± 68 Mt of organic carbon (OC) and 2,582 ± 168 Mt of inorganic carbon (IC). The spatial mapping of this C highlights well-defined OC accumulation hotspots in fjords, estuaries and coastal muds, while large accumulations of IC are found in the tidally swept areas around Orkney, Shetland and the South West of England. Within the well-defined OC hotspots, muddy sediments store the greatest quantity of OC; the muds offer potentially valuable opportunities for targeted future management and protection of sedimentary C stores within the UK EEZ. In the future, if areas of the seafloor were to be managed to include the protection of these valuable sedimentary C resources, we recommend an initial focus on hotspots of high sedimentary OC density.

This paper investigates a mathematical model of competition between two species for inorganic carbon and light in a well-mixed water column. The population growth of the species depends on the consumption of two substitutable forms of inorganic carbon, "CO2" (dissolved CO2 and carbonic acid) and "CARB" (bicarbonate and carbonate ions), which are stored internally. Besides, uptake rates also includes self-shading by the phytoplankton population, that is, an increase in population density will reduce light available for photosynthesis, and thereby reducing further carbon assimilation and population growth. We also incorporate the fact that carbon is lost by respiration, and the respiration rate is assumed to be proportional to the size of the transient carbon pool. Then we study the extinction and persistence of a single-species system. Finally, we show that coexistence of the two-species system is possible, depending on parameter values, and both persistence of one population.

Mass transfer parameters are necessary for the design of absorption and desorption processes in packed columns. To determine the effective interfacial area and liquid side mass transfer parameters, CO2 absorption and desorption are frequently used. Reliable analytics for concentration determination are essential to obtain correct results. In this work two methods of CO2 liquid phase analysis are compared: first, the back titration of unreacted NaOH after prior precipitation of the bound CO2; secondly, the inorganic carbon analysis with a commercial inorganic carbon analyzer. [ABSTRACT FROM AUTHOR]

Summary: Cell size influences the rate at which phytoplankton assimilate dissolved inorganic carbon (DIC), but it is unclear whether volume‐specific carbon uptake should be greater in smaller or larger cells. On the one hand, Fick's Law predicts smaller cells to have a superior diffusive CO2 supply. On the other, larger cells may have greater scope to invest metabolic energy to upregulate active transport per unit area through CO2‐concentrating mechanisms (CCMs).Previous studies have focused on among‐species comparisons, which complicates disentangling the role of cell size from other covarying traits. In this study, we investigated the DIC assimilation of the green alga Dunaliella tertiolecta after using artificial selection to evolve a 9.3‐fold difference in cell volume. We compared CO2 affinity, external carbonic anhydrase (CAext), isotopic signatures (δ13C) and growth among size‐selected lineages.Evolving cells to larger sizes led to an upregulation of CCMs that improved the DIC uptake of this species, with higher CO2 affinity, higher CAext and higher δ13C. Larger cells also achieved faster growth and higher maximum biovolume densities.We showed that evolutionary shifts in cell size can alter the efficiency of DIC uptake systems to influence the fitness of a phytoplankton species. [ABSTRACT FROM AUTHOR]

The data on stress-related changes in the expression and activity of plant carbonic anhydrases (CAs) suggest that they are generally upregulated at moderate stress severity. This indicates probable involvement of CAs in adaptation to drought, high salinity, heat, high light, Ci deficit, and excess bicarbonate. The changes in CA levels under cold stress are less studied and generally represented by the downregulation of CAs excepting βCA2. Excess Cd2+ and deficit of Zn2+ specifically reduce CA activity and reduce its synthesis. Probable roles of βCAs in stress adaptation include stomatal closure, ROS scavenging and partial compensation for decreased mesophyll CO2 conductance. βCAs play contrasting roles in pathogen responses, interacting with phytohormone signaling networks. Their role can be either negative or positive, probably depending on the host–pathogen system, pathogen initial titer, and levels of ·NO and ROS. It is still not clear why CAs are suppressed under severe stress levels. It should be noted, that the role of βCAs in the facilitation of CO2 diffusion and their involvement in redox signaling or ROS detoxication are potentially antagonistic, as they are inactivated by oxidation or nitrosylation. Interestingly, some chloroplastic βCAs may be relocated to the cytoplasm under stress conditions, but the physiological meaning of this effect remains to be studied. [ABSTRACT FROM AUTHOR]

The anammox process is an energy efficient promising alternative to biologically remove the nitrogen. Thus, a 5-L anammox granular reactor was inoculated with sludge coming from a sidestream partial nitritation and anammox reactor (>200 mg TN/L and 30 °C) and it was directly subjected to 15 ± 1 °C treating mimicked municipal wastewater (50 mg TN/L). Results indicated that an acclimation period (commonly used) to progressive reach the mainstream conditions is not needed, shortening the start-up periods. The long-term anammox process stability was proved to treat synthetic wastewater with decreasing alkalinities and nitritified primary settled municipal wastewater. The low pH values (6.2 ± 0.1) of the municipal wastewater fed did not affect the process stability. Residual organic matter concentrations augmented the nitrogen removal efficiency from 80 % (with the synthetic medium) to 92 % achieving effluent concentrations below 10 mg TN/L. Finally, the effect of pH (6–8), temperature (15–30 °C) and organic matter concentration (0–75 mg TOC/L) over the specific anammox activity (SA AMX) was evaluated at short-term. pH and temperature and their interactions exerted significant influence on the SA AMX value while the TOC concentrations itself did not significantly change the SA AMX. [ABSTRACT FROM AUTHOR]

This work aimed to verify the effects of adding CO2 and irradiance to Kappaphycus alvarezii cultivation. Thalli were cultured in vitro for 2 weeks under low irradiance (50 μmol photons m−2 s−1) with the addition of CO2 according to the following concentrations: 142× 103 ppm (1CO2, 0.1 L min−1), 285 × 103 ppm (2CO2, 0.2 L min−1) and 428 × 103 ppm (3CO2, 0.3 L min−1), followed by culture under higher irradiance (200 μmol photons m−2 s−1) for 2 more weeks. Control had no CO2 addition. Afterwards, growth rate, chlorophyll a and carotenoid content were quantified. Samples were submitted to light microscopy and transmission electron microscopy. Growth rates of different treatments or control between experimental periods showed no significant differences, except for 2CO2 treatment at the end of each period. Kappaphycus alvarezii cultivated with CO2 addition showed cell wall thickening and increasing quantity of starch granules, chlorophyll a and carotenoids compared with control. Exposed to high irradiance, control samples showed signs of stress, such as changes in chloroplast, starch granules quantity decrease and total chlorophyll a and carotenoids increase. Samples cultivated with CO2 showed an increase in the quantity and size of the starch granules and an increase in the number of organelles (mitochondria) related to energy generation and cell construction (Golgi complex). Such alterations suggest cellular response after CO2 addition, such as the formation of starch reserves and cell wall thickening, which could make plants more tolerant to environmental stress during transport from indoor condition to sea farms. [ABSTRACT FROM AUTHOR]

Landscapes of the northern part of the Bolshoi Paipudynskii Ridge (the Polar Urals) served as a key site to study the taxonomic diversity of soils on calcareous rocks as related to both bioclimatic and geogenic (relief, thickness of eluvial and colluvial derivatives of calcareous rocks) factors. Soils of the postlithogenic trunk of the new Russian soil classification system are developed under different plant communities. They are classified within several soil orders: cryometamorphic soils (Mollic Calcaric Stagnosols), lithozems (Folic Mollic Calcaric Leptosols), organo-accumulative soils (Molic Leptic Calcaric Stagnosols), and gley soils (Folic Calcaric Gleysols). These soils compose either small individual areas, or occur in soil associations. The mass of carbon and nitrogen in the aboveground phytomass ranges within 40–49 and 0.9–2.3%, respectively. The storage of aboveground phytomass (fresh weight) varies from 20 to 1600 g/m2. In each soil profile, the surface horizons have a maximum content of organic carbon and nitrogen (up to 40 and 2.5%, respectively). The Corg and Norg patterns in soils depend on the productivity of plant communities, the composition of falloff, and the conditions for its decomposition. In all soil profiles, the inorganic carbon content (Cinorg) increases down the soil profile reaching 12%. The mineral nitrogen content does not exceed 1%. The contents of N- and N- have their maximums reaching 140 and 30 mg/kg, respectively, in the surface soil horizons. [ABSTRACT FROM AUTHOR]

Main conclusion: β-carbonic anhydrases, which function in regulating plant growth, C/N status, and stomata number, showed functional redundancy and divergence in Physcomitrella patens. Carbonic anhydrases (CAs) catalyze the interconversion of CO2 and HCO3−. Plants have three evolutionarily unrelated CA families: α-, β-, and γ-CAs. βCAs are abundant in plants and are involved in CO2 assimilation, stress responses, and stomata formation. Recent studies of βCAs have mainly examined C3 or C4 plants, whereas their functions in non-vascular plants are mostly unknown. In this study, phylogenetic analysis revealed that the evolution of βCAs were conserved between subaerial green algae and bryophytes after terrestrialization event, and βCAs from some cyanobacteria might begin evolving for the adaptation of terrestrial environment/habitat. In addition, we investigated the physiological roles of βCAs in the basal land plant Physcomitrella patens. High PpβCA expression levels in different tissues suggest that PpβCAs play important roles in development in P. patens. Plants treated with 1–10 mM NaHCO3 had higher fresh and dry weight, PpβCA expression, total CA activity, and photosynthetic yield (Fv/Fm) compared with water-treated plants. However, treatment with 10 mM NaHCO3 influenced the C/N status. Further study of six Ppβca single-gene mutants revealed that PpβCAs have functional redundancy and divergence in regulating the C/N ratio of plants and stomatal formation. This study provides new insight into the physiological roles of βCAs in basal land plants. [ABSTRACT FROM AUTHOR]

Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity, global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbons is thus of great necessity. Although the best method is still disputable, the acid leaching method is widely used in many laboratories because of its ease-of-use and high accuracy. The results of the elemental analysis of sediment trap samples reveal that organic and inorganic carbon contents cannot be obtained using the acid leaching method, causing an infinitely amplified error when the carbon content of the decarbonated sample is 12%±1% according to a mathematical derivation. Acid fumigation and gasometric methods are used for comparison, which indicates that other methods can avoid this problem in organic carbon analysis. For the first time, this study uncovers the pitfalls of the acid leaching method, which limits the implication in practical laboratory measurement, and recommends alternative solutions of organic/inorganic carbon determination in marine sediments. [ABSTRACT FROM AUTHOR]

Global change includes invasion by exotic (nonnative) plant species and altered precipitation patterns, and these factors may affect terrestrial carbon (C) storage. We measured soil C changes in experimental mixtures of all exotic or all native grassland plant species under two levels of summer drought stress (0 and +128 mm). After 8 yr, soils were sampled in 10‐cm increments to 100‐cm depth to determine if soil C differed among treatments in deeper soils. Total soil C (organic + inorganic) content was significantly higher under native than exotic plantings, and differences increased with depth. Surprisingly, differences after 8 yr in C were due to carbonate and not organic C fractions, where carbonate was ~250 g C/m2 lower to 1‐m soil depth under exotic than native plantings. Our results indicate that soil carbonate is an active pool and can respond to differences in plant species traits over timescales of years. Significant losses of inorganic C might be avoided by conserving native grasslands in subhumid ecosystems. [ABSTRACT FROM AUTHOR]

Hurricanes can alter the rates and trajectories of biogeochemical cycling in coastal wetlands. Defoliation and vegetation death can lead to increased soil temperatures, and storm surge can variously cause erosion or deposition of sediment leading to changes in soil bulk density, nutrient composition, and redox characteristics. The objective of this study was to compare the biogeochemistry of pre-storm soils and a carbonate-rich sediment layer deposited by Hurricane Irma that made landfall in southwest Florida as a category 3 storm in September 2017. We predicted that indicators of biogeochemical activity (e.g., potential soil respiration rates, microbial biomass (MBC), and extracellular enzyme activities) would be lower in the storm sediment layer because of its lower organic matter content relative to pre-storm soils. There were few differences between the storm sediment and pre-storm soils at two of the sites closest to the Gulf of Mexico (GOM). This suggests that marine deposition regularly influences soil formation at these sites and is not something that occurs only during hurricanes. At a third site, 8 km from the GOM, the pre-storm soils had much greater concentrations of organic matter, total N, total P, MBC, and higher potential respiration rates than the storm layer. At this same site, CO2 fluxes from intact soil cores containing a layer of storm sediment were 30% lower than those without it. This suggests that sediment deposition from storm surge has the potential to preserve historically sequestered carbon in coastal soils through reduced respiratory losses. [ABSTRACT FROM AUTHOR]

Increasing soil carbon (C) in arable soils is an important strategy to achieve sustainable yields and mitigate climate change. We investigated changes in soil organic and inorganic carbon (SOC and SIC) under conservation agriculture (CA) in a calcareous soil of the eastern Indo‐Gangetic Plains of India. The treatments were as follows: conventional‐till rice and wheat (CT‐CT), CT rice and zero‐till wheat (CT‐ZT), ZT direct seeded rice (DSR) and CT wheat (ZT‐CT), ZTDSR and ZT wheat without crop residue retention (ZT‐ZT), ZT‐ZT with residue (ZT‐ZT+R), and DSR and wheat both on permanent beds with residue (PB‐PB+R). The ZT‐ZT+R had the highest total SOC in both 0–15 and 15–30 cm soil layers (20% and 40% higher (p <.05) than CT‐CT, respectively), whereas total SIC decreased by 11% and 15% in the respective layers under ZT‐ZT+R compared with CT‐CT. Non‐labile SOC was the largest pool, followed by very labile, labile and less labile SOC. The benefits of ZT and residue retention were greatest for very labile SOC, which showed a significant (p <.05) increase (~50%) under ZT‐ZT+R compared with CT‐CT. The ZT‐ZT+R sequestered ~2 Mg ha−1 total SOC in the 0–15 cm soil layer in 6 years, where CT registered significant losses. Thus, the adoption of CA should be recommended in calcareous soils, for C sequestration, and also as a reclamation technique. [ABSTRACT FROM AUTHOR]

Summary: In response to high CO2 environmental variability, green algae, such as Chlamydomonas reinhardtii, have evolved multiple physiological states dictated by external CO2 concentration. Genetic and physiological studies demonstrated that at least three CO2 physiological states, a high CO2 (0.5–5% CO2), a low CO2 (0.03–0.4% CO2) and a very low CO2 (< 0.02% CO2) state, exist in Chlamydomonas. To acclimate in the low and very low CO2 states, Chlamydomonas induces a sophisticated strategy known as a CO2‐concentrating mechanism (CCM) that enables proliferation and survival in these unfavorable CO2 environments. Active uptake of Ci from the environment is a fundamental aspect in the Chlamydomonas CCM, and consists of CO2 and HCO3– uptake systems that play distinct roles in low and very low CO2 acclimation states. LCI1, a putative plasma membrane Ci transporter, has been linked through conditional overexpression to active Ci uptake. However, both the role of LCI1 in various CO2 acclimation states and the species of Ci, HCO3– or CO2, that LCI1 transports remain obscure. Here we report the impact of an LCI1 loss‐of‐function mutant on growth and photosynthesis in different genetic backgrounds at multiple pH values. These studies show that LCI1 appears to be associated with active CO2 uptake in low CO2, especially above air‐level CO2, and that any LCI1 role in very low CO2 is minimal. Significance Statement: LCI1 is a novel plasma membrane Ci transporter involved in active Ci uptake to support the Chlamydomonas CO2‐concentrating mechanism (CCM), although its precise function is unknown. By analyzing Ci‐dependent O2 evolution responses of an LCI1 loss‐of‐function mutant in different genetic backgrounds and pH values, we reveal a specific role for LCI1 in active CO2 uptake in the low CO2 range, especially above air‐level CO2. [ABSTRACT FROM AUTHOR]

Summary: In response to high CO2 environmental variability, green algae, such as Chlamydomonas reinhardtii, have evolved multiple physiological states dictated by external CO2 concentration. Genetic and physiological studies demonstrated that at least three CO2 physiological states, a high CO2 (0.5–5% CO2), a low CO2 (0.03–0.4% CO2) and a very low CO2 (< 0.02% CO2) state, exist in Chlamydomonas. To acclimate in the low and very low CO2 states, Chlamydomonas induces a sophisticated strategy known as a CO2‐concentrating mechanism (CCM) that enables proliferation and survival in these unfavorable CO2 environments. Active uptake of Ci from the environment is a fundamental aspect in the Chlamydomonas CCM, and consists of CO2 and HCO3– uptake systems that play distinct roles in low and very low CO2 acclimation states. LCI1, a putative plasma membrane Ci transporter, has been linked through conditional overexpression to active Ci uptake. However, both the role of LCI1 in various CO2 acclimation states and the species of Ci, HCO3– or CO2, that LCI1 transports remain obscure. Here we report the impact of an LCI1 loss‐of‐function mutant on growth and photosynthesis in different genetic backgrounds at multiple pH values. These studies show that LCI1 appears to be associated with active CO2 uptake in low CO2, especially above air‐level CO2, and that any LCI1 role in very low CO2 is minimal. Significance Statement: LCI1 is a novel plasma membrane Ci transporter involved in active Ci uptake to support the Chlamydomonas CO2‐concentrating mechanism (CCM), although its precise function is unknown. By analyzing Ci‐dependent O2 evolution responses of an LCI1 loss‐of‐function mutant in different genetic backgrounds and pH values, we reveal a specific role for LCI1 in active CO2 uptake in the low CO2 range, especially above air‐level CO2. [ABSTRACT FROM AUTHOR]

The vertical distribution and exchange mechanisms of soil organic and inorganic carbon (SOC, SIC) play an important role in assessing carbon (C) cycling and budgets. However, the impact of land use through time for deep soil C (below 100 cm) is not well known. To investigate deep C storage under different land uses and evaluate how it changes with time, we collected soil samples to a depth of 500 cm in a soil profile in the Gutun watershed on the Chinese Loess Plateau (CLP); and determined SOC, SIC, and bulk density. The magnitude of SOC stocks in the 0–500 cm depth range fell into the following ranking: shrubland (17.2 kg m−2) > grassland (16.3 kg m−2) > forestland (15.2 kg m−2) > cropland (14.1 kg m−2) > gully land (6.4 kg m−2). The ranking for SIC stocks were: grassland (104.1 kg m−2) > forestland (96.2 kg m−2) > shrubland (90.6 kg m−2) > cropland (82.4 kg m−2) > gully land (50.3 kg m−2). Respective SOC and SIC stocks were at least 1.6- and 2.1-fold higher within the 100–500 cm depth range, as compared to the 0–100 cm depth range. Overall SOC and SIC stocks decreased significantly from the 5th to the 15th year of cultivation in croplands, and generally increased up to the 70th year. Both SOC and SIC stocks showed a turning point at 15 years cultivation, which should be considered when evaluating soil C sequestration. Estimates of C stocks greatly depends on soil sampling depth, and understanding the influences of land use and time will improve soil productivity and conservation in regions with deep soils. [ABSTRACT FROM AUTHOR]

The marine red macroalga Gracilaria lemaneiformis usually experiences a changing carbonate system during mariculture. Thalli of G. lemaneiformis collected from Nanao Island, Shantou, China, were cultured in six treatments, with two inorganic carbon (Ci) levels (ambient-Ci, AC; elevated-Ci, EC) and three pH levels (8.2, 9.0, and 9.4), to examine the influence of increased Ci concentrations and high seawater pH on growth and photosynthesis in this farmed algal species. The capacity to extract HCO3− from seawater was relatively stable, as pH compensation points of G. lemaneiformis remained unchanged (9.54–9.59) in the six treatments. Relative growth rate (RGR) and net photosynthetic rate (Pn) of G. lemaneiformis showed no significant differences between treatments of AC and EC at pH 8.2. However, RGR and Pn were higher at EC than at AC at pH 9.4. In addition, RGR and Pn at AC treatments were 67% ± 12% and 76% ± 6% lower at pH 9.4 than at pH 8.2, respectively. At AC, total pigment content, effective quantum yield of PSII (Yield), and maximum relative electron transport rate (rETRm) were all lower at pH 9.4 than at 8.2. However, reductions of these parameters were significantly ameliorated when thalli of G. lemaneiformis were cultured at EC conditions. We conclude that increasing atmospheric CO2 is conducive to the aquaculture of G. lemaneiformis through the decline of pH and the concurrent increase of Ci in seawater. [ABSTRACT FROM AUTHOR]

The amounts and characteristics of carbon (C) transported by streams and rivers are strongly connected to attributes of their associated watersheds. However, the factors controlling how different land uses influence the sources and inputs of organic and inorganic C to headwater streams are not fully understood. In order to assess how land use practices specifically influence headwater stream C, the concentrations and isotopic (natural δ13C and ∆14C) signatures of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate organic C (POC) were measured between October 2008 and August 2009 in streams of six small watersheds of differing land use. Bayesian mixing models were used to estimate contributions of potential C sources to stream DIC, DOC, and POC pools. Mixing model results indicate that sources of C to streams in tilled and non-tilled corn watersheds were dominated by C4 plant biomass and soil organic C. In all other watershed types stream C was dominated by C3 plant biomass. In addition, δ13C and Δ14C values of forested stream C were unique from values in the corn, pasture, and large mixed use watersheds, and showed greater contributions from modern-aged C3 biomass. Relative to other watershed types, tilled corn agriculture showed the greatest effect on both the sources and amounts of stream C. In the tilled corn watersheds, total C (DIC + DOC + POC) fluxes were 314% higher than in the non-tilled corn watershed and 39–76% higher than in all other watersheds. Thus, land use and agricultural practices can serve as strong controls over the sources and fluxes of organic and inorganic C to streams. [ABSTRACT FROM AUTHOR]

This study extends the 1991-1995 records of marine dissolved organic carbon (DOC) concentrations and Δ14C values at hydrographic Station M (34°50′N, 123°00′W) with new measurements from a frozen (-20 °C) archive of samples collected between April 1998 and October 2004. The magnitudes and synchronicity of major Δ14C anomalies throughout the time-series imply transport of DOC from the surface ocean to depths of at least 450 m on the timescale of months. Keeling plots of all measurements at Station M predict a continuum of possible background DOC compositions containing at least 21 μM of -1000‰ (i.e., ≥57,000 14C years) DOC, but are more consistent with mean deep DOC (38 μM, -549‰; i.e., ∼6,400 14C years). These results and coral records of surface dissolved inorganic carbon (DIC) Δ14C were used to estimate pre-bomb DOC Δ14C depth profiles. The combined results indicate that bomb-14C has penetrated the DOC pool to depths of ≥450 m, though the signal at that depth is obscured by short-term variability.

Carbon plays a crucial role in the search for extraterrestrial life and serves as an indicator for the habitability and the paleoatmospheric CO 2 reservoir on Mars. Previous exploration missions provided evidence of carbon on Mars with different chemical speciation using various instruments including laser-induced breakdown spectroscopy (LIBS). Quantitative determination with LIBS onboard Mars rovers is still precluded because of the important contribution of the atmospheric carbon in the LIBS plasma, in addition to matrix effects omnipresent for elemental determination with LIBS of geological materials. In this work, we performed a series of LIBS experiments in a simulated Martian atmosphere using samples prepared with a Martian soil simulant mixed with various carbonates and organic C-bearing materials. Convoluted influences on LIBS spectra due to the ambient gas and the different chemical speciation of carbon were observed for inorganic and organic C-bearing materials, which explains the unsatisfactory performance for a univariate regression model based on a carbon-related emission line. In particular, the influence of ambient gas was observed more important for inorganic carbon brought into the samples with carbonates. Multivariate models were then developed based on a back-propagation neural network (BPNN), for ensembles of samples with inorganic and organic carbons respectively, and then for the fusion of the two ensembles. The results showed respective limits of detection (LODs) of 0.247 wt%, 1.022 wt% and 0.873 wt%, and respective root mean square errors of prediction (RMSEPs) of 0.036 wt%, 0.133 wt%, and 0.062 wt% for the three collections of samples. Moreover, the model training process is investigated in detail in order to understand the way in which the most significant spectral features are selected, processed and mapped to the carbon concentrations of the samples by a neural network. [Display omitted] • Accurate LIBS carbon determination in a Martian soil simulant under the 700 Pa CO 2 atmosphere. • Behaviors of the emissions from inorganic and organic carbons under a simulated Martian atmosphere. • Analysis and interpretation of the features relevant for inorganic and organic carbon regressions. • Effectiveness of a multivariate regression for carbon determination for a set of diverse samples. [ABSTRACT FROM AUTHOR]

• 2.5-5.0 g/L NaHCO 3 favors chain elongation to produce caproate. • Inorganic carbon greatly enhanced the growth and metabolism of chain elongators. • About 15.5% of the organic carbon in food waste can eventually converted to caproate. • Economic and environmental benefits can be realized from food waste chain elongation. In this study, the role of inorganic carbon in chain elongation fermentation was investigated by examining its effects at different carbonate concentrations. The results demonstrated that higher yield of caproate (6.3±0.3 g/L - 7.4±0.2 g/L) was achieved with a NaHCO 3 concentration of 2.5-5.0 g/L. Building upon these findings, a chain elongation process for food waste was developed. The caproate productions of control, CO 2 and Na 2 CO 3 trials were 4.6±0.2 g/L, 7.3±0.1 g/L, and 8.3±0.2 g/L, respectively. Chain elongation fermentation of food waste (1t TS) with Na 2 CO 3 enhancement could synthesize 116.9 kg of caproate and 72.5 kg of carbon could be converted in caproate, accounting for 15.5% of the total organic carbon in the food waste. This study provided a comprehensive exploration of the chain elongation process for food waste, offering insights for further optimization and enhancement of food waste chain elongation performance coupling inorganic carbon utilization. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Introduction The Florida Everglades has undergone significant ecological change spanning the continuum of disturbance to restoration. While the restoration effort is not complete and the ecosystem continues to experience short duration perturbations, a better understanding of long-term C dynamics of the Everglades is needed to facilitate new restoration efforts. This study evaluated temporal trends of different aquatic carbon (C) pools of the northern Everglades Protection Area over a 20-year period to gauge historic C cycling patterns. Dissolved inorganic C (DIC), dissolved organic C (DOC), particulate organic C (POC), and surface water carbon dioxide (pCO2(aq)) were investigated between May 1, 1994 and April 30, 2015. Results Annual mean concentrations of DIC, DOC, POC, and pCO2(aq) significantly decreased through time or remained constant across the Water Conservation Areas (WCAs). Overall, the magnitude of the different C pools in the water column significantly differed between regions. Outgassing of CO2 was dynamic across the Everglades ranging from 420 to 2001 kg CO2 year−1. Overall, the historic trend in CO2 flux from the marsh declined across our study area while pCO2(aq) largely remained somewhat constant with the exception of Water Conservation Area 2 which experienced significant declines in pCO2(aq). Particulate OC concentrations were consistent between WCAs, but a significantly decreasing trend in annual POC concentrations was observed. Conclusions Hydrologic condition and nutrient inputs significantly influenced the balance, speciation, and flux of C pools across WCAs suggesting a subsidy-stress response in C dynamics relative to landscape scale responses in nutrient availability. The interplay between nutrient inputs and hydrologic condition exert a driving force on the balance between DIC and DOC production via the metabolism of organic matter which forms the base of the aquatic food web. Along the restoration trajectory as water quality and hydrology continues to improve, it is expected that C pools will respond accordingly.

This study illustrated the growth of Scenedesmus obliquus and recycle of nutrients in wastewater combined with inorganic carbon under autotrophic conditions. Scenedesmus obliquus was cultivated under different conditions by adding sodium carbonate (Na2CO3) at 15–40 mg l−1 separately in wastewater containing high nitrogen and phosphorus content. The growth characteristics of S. obliquus, pH and dissolved inorganic carbon (DIC) changes of microalgae liquid, the recycle rate of ammonia and phosphorus and lipid content were determined. The changes of pH and DIC showed that S. obliquus could use Na2CO3 to grow, with lipid contents of 18–25%. Among all Na2CO3 concentrations, 20 mg l−1 was the optimum, of which S. obliquus had the highest NH3-N recycle of 52% and PO43–P recycle of 67%. By the 14th day, its biomass production also reaches the maximum of 0.21 g l−1. However, inorganic carbon fixation rate was inversely proportional to its concentration. Moreover, the biomass was in positive correlation with the Na2CO3 concentration except 20 mg l−1, which provided a possibility that S. obliquus could be acclimatized to adjust to high concentrations of inorganic carbon to promote biomass accumulation and recycle of nutrients.

Current algal-bacterial consortia require high hydraulic retention times (HRTs, 2–10 days) to efficiently remove pollutants from domestic wastewaters. A novel algal-bacterial biofilm reactor was developed for a much lower HRT. The results showed that an HRT of 12 h ensured 90% removal of organic matter and ammonium, and phosphate removal was approximately 30%. Decreasing the HRT to 8 h significantly deteriorated the reactor's pollutant removal efficiencies and increasing the HRT to 24 h did not improve these efficiencies. Illumination, which was light source for algae, was provided by a LED light. Activity tests showed that organic matter and ammonium removal rates resulting from illumination were 70% and 50%, respectively, of the rates when dissolved oxygen concentration was maintained at 2 mg/L. Chemical oxygen demand (COD) removal rates resulted from illumination and aeration were 18.63 and 25.38 mg COD/L.h, respectively. The phosphate removal rate was 0.26 and 0.43 mg/L.h when illumination and aeration were applied, respectively. The ammonium removal rates were approximately 10,390 and 5000 mg NH 4 + − N / m 2. d when the reactor was aerated or illuminated, respectively. These two rates were significantly higher than reported nitrification rates. Moreover, the percentage of Oscillatoria sp. increased from below 10% to over 90% under the applied organic load and temperature, while the percentage of fast growing algae, Chlorella, chroococcus sp and Scenedesmus sp., decreased from over 90% to below 10%. These results showed that an algal-bacterial biofilm reactor with a low reactor footprint was developed. [ABSTRACT FROM AUTHOR]

Mineral carbonation of alkaline earth metals is the conversion of carbon dioxide, in gaseous form or dissolved in water, to form solid inorganic carbonates. Alkaline earth metals can be derived from natural minerals, waste residues, or brines. Calcium and magnesium are the two most abundant of these metals, which when carbonated form a variety of calcium and magnesium carbonates of different mineral compositions and crystal structures. Determining inorganic carbon (IC) content of carbonation solid products with high precision is an essential requisite to quantify the amount of carbon dioxide sequestered by a given process at a given reaction time. It also enables understanding fundamental phenomena about the reactions, including the reaction rate, conversion limitations, and the mineral composition of carbonation products and by-products. The most conventional methods to determine IC content utilize destructive techniques based on acid decomposition (e.g. calcimeter) and thermal decomposition (e.g. thermogravimetric analyzer). The main disadvantage of these methods includes chemical usage, long measurement time, overestimation of IC, and limited ability to differentiate the various mineral forms of carbonates. In this regard, nondestructive techniques (NDT) constitute a valuable alternative to the conventional method for IC determination and carbonates characterization; these include spectroscopic methods (NIR, MIR), X-ray spectroscopy (XRD, XRF, XCT); and microscopic methods (SEM-EDS, TEM, RLM, EPMA). While infrared spectroscopy can be used to quantitatively identify carbonate spectral bands, X-ray diffraction quantitatively identifies the presence of specific crystalline carbonate phases. Elemental chemical information is provided by X-ray fluorescence, and microstructure analysis is done using electron probe microanalysis and micro-tomography. SEM provides visualization of crystal and particle size and morphology, while energy dispersive spectroscopy is used to inspect elemental composition of individual particles or intra-particle layers and grains. This paper presents a critical comparative analysis of the use of these NDT in determining IC content and carbonate composition. Improved understanding of the advantages, limitations, and applicability of each method can enable the development of standard protocols for characterization of carbonation products, which is especially required for carbon sequestration accounting in view of climate change mitigation. Unlabelled Image • Accurate, precise and efficient inorganic carbon determination need is discussed. • Techniques based on acid and thermal decomposition do not differentiate carbonates. • Non-destructive techniques evaluate mineralogy, micro-structure and speciation. • Complementary techniques provide mechanistic insights on enhanced weathering. • Learnings from slag carbonation research are informative for weathering research. [ABSTRACT FROM AUTHOR]

• We examined the carbon pools and fluxes in a carbonate-rich coastal ecosystem. • The C sink of the chenier plain is comparable to that of organic-rich salt marshes. • The chenier plain had a net CO 2 evasion during the entire soil formation process. • Plant growth and succession enhance organic carbon accumulation in a chenier plain. • Inorganic carbon storage should be considered in blue carbon inventories. Coastal wetlands play an important role in the global carbon cycle because they have high ecosystem productivity and carbon sequestration capability. Previous research focused on the carbon dynamics of organic-rich ecosystems (e.g., salt marshes, mangroves), while little attention has paid to the carbon cycling of carbonate-rich ecosystems such as chenier plains, sandy or shelly beach ridges that are parts of strand plains. Here we examined the carbon stocks and fluxes of the poorly studied chenier plain in the Yellow River Delta, China. The inorganic and organic carbon pools in the top 1 m sediment were 444 ± 92 Mg C ha−1 and 89 ± 7 Mg C ha−1, respectively. The average CO 2 net sequestration was −177 ± 51 Mg C ha−1, indicating that the chenier plain had a net CO 2 evasion during the entire soil formation process. With plant growth, however, the chenier plain provided a significant carbon sink (395 g C m−2 a−1) on a per-unit area basis. The annual gross ecosystem productivity (GEP) and ecosystem respiration (R e) were 1067 and 672 g C m−2 a−1, respectively. The carbon sink strength of the chenier plain was comparable to that of organic-rich salt marshes on a per-unit area basis. The biomass carbon pool was 5.0 ± 1.4 Mg C ha−1 in the chenier plain. Moreover, the sediment inorganic carbon content in mudflats was significantly lower than that of vegetated habitats. Our results showed that plant grown in a chenier plain could significantly enhance carbon sequestration by increasing organic carbon storage. Inorganic carbon storage should be considered in blue carbon inventories because inorganic carbon dominates the carbon pool and is important in the carbon cycling in a chenier plain. Our findings can help us better understand the carbon cycling of carbonate-rich coastal ecosystems and can inform chenier plain conservation and restoration efforts. [ABSTRACT FROM AUTHOR]

Anolyte acidification is inevitable in the operation of buffer-free microbial fuel cells (MFCs), which restricts the proliferation and metabolism of electroactive bacteria, and results in electric-power deterioration. The anodic metabolic end-products, inorganic carbons (IC), which are composed of H 2 CO 3 (dissolved CO 2), HCO 3 −, and CO 3 2−, are ideal endogenous buffers, whereas the naturally accumulated IC are far from enough to prevent anolyte acidification. In this work, different volume ratios of the anolytes (10%, 30%, and 50%) were recycled to increase the IC concentrations of the single-chamber air-cathode buffer-free MFCs. Under anolyte recycling running mode, IC accumulation agreed with the SGompertz model and the fitting IC-asymptotic concentrations (IC AC) grew exponentially to 18.5 mM, 24.4 mM, and 32.8 mM as the anolyte recycling ratio increased from 10% to 30% and 50%. Self-buffering running can be realized when the anolyte recycling ratio exceeds 50% for the MFC feeding on 1 g·L−1 of acetate. The electric power for the 50% recycling scenario increased from the baseline control of 272.4 mW·m−2 to 628.5 mW·m−2. The coulombic efficiency (CE) was also apparently improved. This paper for the first time clarifies the accumulation law of endogenous IC buffers under anolyte partially recycling mode and their self-buffering effects. Unlabelled Image • Self-buffering operation was realized through anolyte partially recycling. • IC accumulates by the SGompertz model in MFCs running in anolyte recycling mode. • Electric power of the MFC running with 50% recycled anolyte increased by 2.3 times. [ABSTRACT FROM AUTHOR]

Soil inorganic carbon (SIC) is the most common form of carbon in arid and semiarid regions, where afforestation is used to combat soil degradation. However, response of SIC to afforestation has been studied rarely, which hinders any prediction about soil carbon dynamics. To determine the response of SIC and soil organic carbon (SOC) to afforestation in semiarid soils and whether such responses vary with soil aggregates, soil texture, and climatic conditions, we measured SIC and SOC in bulk soils and aggregate fractions under paired afforested lands and farmlands at five sites across the Loess Plateau. The relationship of these responses to soils and climatic variables was analyzed. Afforestation increased SOC at all sites, with accumulation rates of 0.21, 0.23, 0.34, and 0.09 g kg−1 yr−1 in bulk soils, macroaggregates (>0.25 mm), microaggregates (0.25–0.053 mm), and silt + clay fraction, respectively, when averaged across sites and soil depths. However, the response of SIC to afforestation varied with site, with increased SIC in drier sites and decreased SIC in wetter sites. Change in SIC was negatively correlated with change in SOC either across or within bulk soils and aggregate fractions. The SIC decreased and SOC increased with increasing soil clay content, precipitation, temperature, and site aridity index. These results indicated consistent increase in SOC but variable response of SIC to afforestation among sites in the Loess Plateau. Such variable response of SIC should be incorporated into carbon cycle models to reduce uncertainties when predicting sequestration dynamics of soil carbon. [ABSTRACT FROM AUTHOR]