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Tidal marshes are an important transition zone connecting marine, freshwater, and terrestrial ecosystems. Tidal marshes are known to be sensitive to global climate change such as elevated CO2 and warming. In particular, it is yet to be revealed whether the such change may increase or decrease carbon stock in tidal marshes. Although soil microorganisms play an important role in carbon storage in tidal marshes by determining carbon mineralization, little is known about the interactive effects of elevated CO2 and warming on soil microbial communities in field conditions. Here, we elucidate the effects of 6-year experiment of climate manipulation on soil microbial communities in a tidal marsh. The manipulation experiment included 4 treatments of 1) elevated atmospheric CO2 concentrations (750 ppm) only, 2) warming (+5.1 °C) only, 3) both elevated CO2 and warming, and 4) ambient conditions. Elevated CO2 significantly changed the structure of the RNA-derived (active) and DNA-derived (total) soil microbial community, but warming did not affect either. The relative abundances of Acidobacteria, Actinobacteria, Chloroflexi, and Planctomycetes were higher in the DNA-derived soil microbial communities than in the RNA-derived soil microbial communities, whereas those of Campilobacterota, Desulfobacteria, Gammaproteobacteria, Myxococcota, and Spirochaetota were higher in the RNA-derived soil microbial communities. In addition, elevated CO2 changed the microbial communities from r- to K-strategists in both RNA and DNA-derived communities, suggesting that this may offset additional C input by roots in a future elevated atmospheric CO2 environment. This study provides a better understanding of microbial response to the combined effects of elevated atmospheric CO2 concentrations and global warming in the tidal marsh ecosystems.

Peatlands are a globally important carbon sink, storing up to 455 Pg C as soil organic carbon. One of the drivers of this immense storage relates to the extremely low rate of peat decomposition, which is ultimately regulated by the bacterial community of these peat soils. Previous studies note that vegetation type (e.g., bog vs. fen), depth of peat, water level and pH may determine bacterial composition in peatlands. However, in terms of global patterns, the key controlling variables remain elusive due to a lack of data synthesis and direct experimental evidence. To identify bacterial community composition in global peatlands and key controlling variables, we conducted a field survey of 7 peatland sites in Korea, a meta-analysis of published data from over 95 peatland sites, and pH-manipulation experiments in the UK, by employing NGS analysis targeting 16sRNA.Although immense variabilities in bacterial composition among sites were observed, pH appears to be a dominant controlling variable shaping bacterial community structure. For example, high pH is associated with higher relative abundance of Proteobacteria, while low pH appears to be related to the abundance of Acidobacteria. Variations of bacterial composition at different depths or vegetation types in a single site are smaller than those among different locations, suggesting that environmental changes in local conditions such as water level fluctuation and carbon availability may be less critical than the mean temperature or overall pH of a given site. Our study further suggests that the long-term changes in pH may have much greater implications than previously assumed, with peat decomposition likely to accelerate during the current recovery from acidification being experienced by peatlands across the world.

Tidal marsh is a large reservoir of soil organic carbon (SOC), considered one of the most efficient natural carbon sinks. However, the future carbon pool of this ecosystem has large variability and uncertainty due to climate change such as temperature rise and elevated atmospheric CO2 concentration. Microbial-mediated SOC decomposition is a key process that regulates the carbon cycle of tidal marsh. This process is largely temperature-dependent, thus understanding the response of temperature sensitivity (Q10) of SOC decomposition to climate change is critical to improving our prediction capability of the tidal marsh carbon cycle and the climate feedback. However, the response of Q10 of SOC decomposition on climate change in tidal marsh ecosystem is yet to be revealed, hampering our prediction capability of the future tidal marsh carbon cycle. Here, we elucidate the effect of warming and elevated CO2 concentration on the Q10 of SOC decomposition at a Salt Marsh Accretion Response to Temperature eXperiment (SMARTX). Surface sediments were collected in 2022 (6 years after manipulation started) from ambient, +5.1℃ (W), elevated CO2 (750ppm, eCO2), and +5.1℃+elevated CO2 (W+eCO2) plots and the Q10 of SOC decomposition was determined. W significantly decreased aerobic SOC decomposition rate most likely due to the labile carbon depletion and thermal adaptation, whereas eCO2 and W+eCO2 increased the aerobic decomposition rate at high temperatures (25 and 30℃). Anaerobic SOC decomposition rate was not affected by W whereas eCO2 and W+eCO2 significantly increased anaerobic decomposition rate at all temperatures. Q10 of aerobic SOC decomposition was not affected by W whereas eCO2 and W+eCO2 significantly increased. Q10 of anaerobic SOC decomposition was not affected by climate change. Overall, our finding demonstrates that elevated CO2 concentration increases the vulnerability of soil carbon stock to warming in tidal marshes, with implications for modeling the future carbon cycle of the ecosystem.

It is essential to reduce methane (CH4) emissions to minimize the contribution of global warming from rice paddies because CH4 contributes approximately 87% to the global warming potential (GWP). An increase in N fertilizer application could reduce CH4 emissions for several reasons: (1) affect the biomass enhancement of crops to store carbon, (2) decrease methanogenesis activity due to increased nitrate respiration, (3) occur nitrate- and nitrite-dependent anaerobic CH4 oxidation. According to the global scale meta-analysis, increasing N application reduces CH4 emissions. However, the reducing effect of nitrogen (N) fertilization on CH4 emissions from rice paddies needs to be confirmed. The changes in CH4 emission induced by N have a reasonably wide margin of error because the research results were not controlled for the direct factors related to CH4 emissions. Hence, although the increased N fertilizer can increase crop productivity and reduce GWP, it is not introduced as an appropriate agricultural practice. To elucidate the effects of N fertilization on CH4 emissions from rice paddies, field-based manipulation experiments were conducted in three regions where N fertilizer was applied under the control of the other factors. In addition, we aimed to identify why CH4 emissions differ depending on the amount of N fertilizer through the result of the microbial-mediated CH4 cycle.Urea was selected as N fertilizer and application rates were at 0, 90, 135, and 180 kg ha-1 (N0, N1, N2, and N3, respectively). Irrigation, rice species (Oryza sativa cv. Samkwang), cultivation period, and input of P, K, Ca, and Si fertilizer were identically managed in 3 sites in Miryang, Wanju, and Hwaseong for three years. DNA/RNA co-extraction was performed using three region’s soil samples in the 3rd year. Real-time qPCR was performed to quantify the mcrA and pmoA gene copy numbers to identify the abundances of methanogens and methanotrophs, respectively.Cumulative CH4 emissions increased with increasing N fertilizer in Miryang. In contrast, cumulative CH4 emissions significantly decreased with increasing N fertilizer application rates in Hwaseong and Wanju. Especially, N2 and N3 showed CH4 emissions lower than N0 in Hwaseong. In Wanju, the decrease in the abundance of mcrA and subsequently methanogenesis after N1 may cause a reduction in CH4 emissions, while in Hwaseong, the increase in quantification of pmoA and the subsequent higher CH4 oxidation may induce a decline in CH4 emissions. In Miryang, higher mcrA may promote methanogenesis and higher CH4 emissions with an increasing N application. The different responses in methanogens and methanotrophs with different N fertilizer application rates could be due to the initial N concentration. The correlation analysis between initial N including ammonium and nitrate and CH4 emissions from the literature showed a negative relationship at a global scale, suggesting the mechanism based on our experimental results is robust in global rice paddies.In conclusion, additional N fertilizer application considering the initial N concentration can not only increase crop yield in rice paddies but also reduce global warming by reducing CH4 emissions.

Ongoing warming due to climate change has generally led to lengthened growing seasons and subsequent changes in evapotranspiration (ET) and streamflow seasonality. This has been well studied in seasonally dry, snowmelt dominated watersheds, but not in humid, temperate forested watersheds without significant seasonal snowmelt. In this study, we investigate how seasonal streamflow patterns have responded to variability in vegetation phenology in the southern Appalachians over the last four decades. We characterize seasonal shifts in low-frequency streamflow peaks using 50th percentiles of cumulative daily precipitation, streamflow, and soil moisture measurements, and investigate interactions with remotely sensed, long-term greenup anomalies in the deciduous-dominated forested watersheds. After removing a dominant precipitation control, one-day earlier greenup is associated with about one-day early spring flow peak at the low-elevation deciduous catchment. This indicates that the strong dependency of seasonal flow regimes on precipitation is mediated by warming-induced extended growing season, especially by early greenup. In contrast, we find less significant correlations of the greenup anomalies on flow percentiles of an adjacent evergreen and a high-elevation deciduous catchment. At a plot scale, similar correlations of cumulative soil moisture days were found only at an upslope topographic position, where precipitation also showed tighter coupling with soil moisture patterns than downslope. This indicates that early greenup in deciduous forests leading to early ET increase, in turn results in early soil moisture dry-down patterned by hillslope positions, and earlier seasonal streamflow peaks and subsequent declines. Our study suggests that spring flow peaks are likely to shift earlier by warming-induced early greenup even in snow-free regions, which has great implications for future freshwater availability in the southeastern US.

Approximately 17% of the land worldwide is considered highly vulnerable to non-native plant invasion, which can dramatically alter nutrient cycles and influence greenhouse gas (GHG) emissions in terrestrial and wetland ecosystems. However, a systematic investigation of the impact of non-native plant invasion on GHG dynamics at a global scale has not yet been conducted, making it impossible to predict the exact biological feedback of non-native plant invasion to global climate change. Here, we compiled 273 paired observational cases from 94 peer-reviewed articles to evaluate the effects of plant invasion on GHG emissions and to identify the associated key drivers. Non-native plant invasion significantly increased methane (CH

Terrestrial ecosystems are typically nitrogen (N) limited, but recent years have witnessed N enrichment in various soil ecosystems caused by human activities such as fossil fuel combustion and fertilizer application. This enrichment may alter microbial processes in soils in a way that would increase the emissions of methane (CH4) and nitrous oxide (N2O), thereby aggravating global climate change. This review focuses on the effects of N enrichment on methanogens and methanotrophs, which play a central role in the dynamics of CH4 at the global scale. We also address the effects of N enrichment on N2O, which is produced in soils mainly by nitrification and denitrification. Overall, N enrichment inhibits methanogenesis in pure culture experiments, while its effects on CH4 oxidation are more complicated. The majority of previous studies reported that N enrichment, especially NH4+ enrichment, inhibits CH4 oxidation, resulting in higher CH4 emissions from soils. However, both activation and neutral responses have also been reported, particularly in rice paddies and landfill sites, which is well reflected in our meta-analysis. In contrast, N enrichment substantially increases N2O emission by both nitrification and denitrification, which increases proportionally to the amount of N amended. Future studies should address the effects of N enrichment on the active microbes of those functional groups at multiple scales along with parameterization of microbial communities for the application to climate models at the global scale.

Wetland ecosystems have low plant diversity, dominated only by one or two types of vegetation. Species with high biomass can easily invade wetlands and the effect of plant invasion on ecosystem process rates has drawn considerable attention within the field of microbial ecology. However, the effects of high biomass plants on microbes, which play a central role in wetland biogeochemistry, are notably understudied. This study investigates the relationship between plant species and their enzyme activities with microbial diversity in wetland ecosystems. Samples were collected from both natural and constructed wetlands to test whether high and low biomass species of submerged aquatic plants would have significant effects on microbial activity and diversity. This study found that plant species with high biomass increased activities of hydrolase activities such as β-glucosidase and N-acetyl-glucosaminidase. Microbial diversity was higher in rhizosphere with two high biomass plant species present compared to one plant species, due to niche competition, as indicated by a higher Shannon–Weaver index value.

Research on niche specialization in the microbial communities of ammonia oxidizers is important for assessing the consequences of vegetation shift on nitrogen (N) cycling. In this study, soils were sampled from three tree stands (needleleaf, mixed, and evergreen broadleaf) from the Hannam experimental forest in South Korea in spring (May 2019), summer (August 2019), autumn (November 2019), and winter (January 2020). Quantitative polymerase chain reaction (qPCR) and high-throughput sequencing were used to measure the abundance and community structure of various nitrifiers: ammonia-oxidizing archaea and bacteria (AOA and AOB, respectively) as well as complete ammonia oxidizers (comammox). Nitrification rates and total ammonia oxidizer abundance were significantly higher in needleleaf forest soil than those in other forest stands, and they were lowest in evergreen broadleaf forest soil. Comammox clade B was most abundant in needleleaf and evergreen broadleaf forest soils, while AOA were significantly more abundant in mixed forest soil. The abundances of comammox clade B and AOA were negatively correlated with dissolved organic carbon. Phylogenetic analysis showed that NT-alpha and NS-gamma-2.3.2 were the most abundant AOA lineages in all the samples. The seasonal of AOA, AOB, and comammox varied with the sites, suggesting the need to examine the combinations of environmental factors when considering the effects of seasonal changes in the environment. Overall, the results suggest that potential vegetation shifts in forest ecosystems might affect nitrification activities by regulating the abundance and community structure of ammonia oxidizers.

Forest soil harbors diverse microbial communities with decisive roles in ecosystem processes. Vegetation shift from needleleaf to broadleaf species is occurring across the globe due to climate change and anthropogenic activities, potentially change forest soil microbial communities and C cycle. However, our knowledge on the impact of such vegetation shift on soil microbial community and activities, and its consequences on forest soil C dynamics are still not well established. Here, we examined the seasonal variation of soil CO

Microbial breakdown of organic matter (OM) is slowed down by different environmental conditions in peatlands, such as low pH, low oxygen availability and presence of phenolic compounds, leading to their recognized carbon storage function (Freeman et al. 2001, Kang et al. 2018). Peatlands are worldwide distributed with environmental conditions and biogeographical legacy varying among regions, which determine different controlling factors of microbial OM degradation and affect carbon cycling and greenhouse gas (GHG) emissions from peat soils. Here, we present the results of a study aimed at investigating the structure and function of microbial communities involved in the OM decomposition in moss-dominated peatlands of tropical (Andes-Paramo, Colombia), temperate (Wales, UK), and arctic (Svalbard, Norway) regions. Prokaryote community, extracellular enzyme activity, and GHG (carbon dioxide, methane, and nitrous oxide) production were assessed in peat soil (first 10 cm depth) collected in one sampling campaign by region (summer north hemisphere). Results showed contrasting prokaryote communities among regions and a clear link between microbial composition and OM degrading metabolism. Arctic peatlands in Svalbard were shallow, circumneutral, with the highest prokaryote diversity (aerobic and anaerobic), an active lignin degradation, production of carbon dioxide, and nitrous oxide. In Wales, peatlands exhibited the lowest pH, an intermediate diversity of prokaryotes, with aerobic and anaerobic groups, and very low OM degrading activity and GHG production. Finally, in the Paramo’s peatlands, the oxygen level was the lowest and consequently prokaryote community was dominated by anaerobic groups with an active anaerobic OM degradation and methane production. Our study is the first, to the extent of our knowledge, giving a comparative view of microbial OM decomposition in peatlands from contrasting and remote regions. Our results highlight the great global diversity of prokaryotes and microbial metabolism and give new lights on the relationship between microbial composition and microbial carbon cycling in peatlands. ReferencesFreeman, C., Ostle, N., Kang, H. 2001. An enzymic “latch” on a global carbon store. Nature 409:149.Kang, H., Kwon, M. J., Kim, S., Lee, S., Jones, T.G., Johncock, A. C., Haraguchi, A., Freeman, C. 2018. Biologically driven DOC release from peatlands during recovery from acidification. Nature Communications 9:1–7.

For the first time, mobile campaign and building monitoring experiments were conducted in downtown Seoul, Korea during the 2018/2019 winter period to assess the possibility of the co-benefit of CO2 emission reduction and air quality improvement. Given that CO2 and air pollutants in cities both originate from fossil fuel combustion, monitoring urban CO2 concentrations using a mobile vehicle and from the top of tall buildings can be a potentially effective approach for diagnosing the air quality. The local enhancement values (△species) related to urban emission sources were estimated by eliminating baseline concentrations. The results obtained showed high correlation coefficients between △CO2 and △air pollutants (i.e., 0.753, 0.505, and 0.525 for △CO, △NOX, and △NO2), confirming the applicability of CO2 as an indicator of air pollutant sources in downtown Seoul. The evaluation of the air quality in the study area using air pollutant ratios, including the ratios of CO and NOX/NO2, relative to CO2 showed that the ratios of △CO, △NOX, and △NO2 relative to △CO2 were 5.76, 1.89, and 0.21 ppb ppm−1. The estimated △NO2/△NOX ratio (11%) and a comparison of the △NOX/△CO2 ratios obtained with those reported for other cities in different countries suggested the possibility of a relationship between the current air quality in downtown Seoul and the use of diesel vehicles. Results suggest that the development of municipal policies aimed at mitigating climate change should consider the co-benefit of air quality improvement so as to ensure the effective reduction of CO2 and air pollutant emissions.

Ongoing warming under climate change generally brought lengthened growing season and subsequent changes in evapotranspiration (ET) seasonality, but its implication in future freshwater regimes is not fully understood. In this study, we investigate how remotely sensed vegetation phenology information has correlated with seasonal flow patterns in the southern Appalachians over the last three decades. We characterize low-frequency seasonal peaks using cumulative 50 percentiles of daily precipitation, streamflow and soil moisture measurements, further related to long-term greenup anomalies in the study site. After removing a dominant precipitation control, the greenup anomalies show a significant correlation with spring flow peak timing at a low-elevation deciduous catchment. This indicates strong dependency of seasonal flow regimes on precipitation was mediated by warming-induced extended growing season, especially by early greenup. At a plot scale, similar correlations were found only at an upslope topographic position, which occupies most of forest landscapes within the catchment. Meanwhile, we found less significant correlations of the greenup anomalies on the flow percentiles at an adjacent evergreen and a high-elevation deciduous catchments. This suggests that early greenup in deciduous forests leading to early ET increases, in turn result in early soil moisture dry-down patterned by hillslope positions, and early seasonal streamflow declines given precipitation. Our study suggests that it is likely that spring flow peak timing in this region continue to be shifted earlier with time by warming-induced early greenup, which would have great implications for understanding future freshwater availability in the southeastern US.

Significant research has been conducted on the effects of soil salinity issue on agricultural productivity. However, limited consideration has been given to its critical effects on soil biogeochemistry (e.g., soil microorganisms, soil organic carbon and greenhouse gas (GHG) emissions), land desertification, and biodiversity loss. This article is based on synthesis of information in 238 articles published between 1989 and 2022 on these effects of soil salinity. Principal findings are as follows: (1) salinity affects microbial community composition and soil enzyme activities due to changes in osmotic pressure and ion effects; (2) soil salinity reduces soil organic carbon (SOC) content and alters GHG emissions, which is a serious issue under intensifying agriculture and global warming scenarios; (3) soil salinity can reduce crop yield up to 58 %; (4) soil salinity, even at low levels, can cause profound alteration in soil biodiversity; (5) due to severe soil salinity, some soils are reaching critical desertification status; (6) innovate mitigation strategies of soil salinity need to be approached in a way that should support the United Nations Sustainable Development Goals (UN-SDGs). Knowledge gaps still exist mainly in the effects of salinity especially, responses of GHG emissions and biodiversity. Previous experiences quantifying soil salinity effects remained small-scale, and inappropriate research methods were sometimes applied for investigating soil salinity effects. Therefore, further studies are urgently required to improve our understanding on the effects of salinity, address salinity effects in larger-scale, and develop innovative research methods.

Combined application of organic amendment with synthetic fertilizer is an emerging management technique for maximized agronomic benefits without drastic soil health effects. However, little attention has been paid to the environmental costs of such management as the primary focus has remained on agronomic outcomes. In present study, we investigated the impacts of three organic amendments including dairy cattle manure (20 t/ha), poultry manure (20 t/ha), and a biochar (30 t/ha) applied along with urea (55 kg-N/ha) on soil N2O fluxes and explored the mechanisms behind N2O emissions. Plots with urea-only application were used as a control. For source partitioning of soil-emitted N2O, we used isotopocule mapping approach. The results showed significantly higher N2O emission rates from manure-treated plots compared with biochar or control treatments plots. The cumulative N2O emissions rates for 125 days from control, biochar, dairy cattle, and poultry treatments were 0.76, 0.70, 0.96, and 1.05 kg N2O-N/ha, respectively. Isotopocule mapping approach revealed that bacterial denitrification was the dominant pathway for temporal high N2O emission events as the fractions of bacterial denitrification ranged between 0.5 and 0.9 among treatments. Soil DNA-based Q-PCR assays showed significant increase in abundance of NO2− reducing denitrifiers in dairy cattle and poultry treated plots suggesting acceleration in N2O emissions was due to shift in the molecular ratios of (nirS + nirK)/nosZ denitrifying bacterial community. In contrast to manure treatments, the combined application of biochar along fertilizer significantly improved soil C contents with a slight decrease in N2O emission rates. Therefore, biochar appeared to be the best option to minimize soil quality loss without additional environmental cost.

Fisheries capture has plateaued, creating ever-greater reliance on aquaculture to feed growing populations. Aquaculture volumes now exceed those of capture fisheries globally1,2, with China dominating production through major land-use change; more than half of Chinese freshwater aquaculture systems have been converted from paddy fields1,3. However, the greenhouse gas implications of this expansion have yet to be effectively quantified. Here, we measure year-round methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) emissions from paddy fields and new, extensively managed crab aquaculture ponds. The conversion increased associated global warming potentials from 8.15 ± 0.43 to 28.0 ± 4.1 MgCO2eq ha−1, primarily due to increased CH4 emissions. After compiling a worldwide database of different freshwater aquaculture systems, the top 21 producers were estimated to release 6.04 ± 1.17 TgCH4 and 36.7 ± 6.1 GgN2O in 2014. We found that 80.3% of the total CH4 emitted originated in shallow earthen aquaculture systems, with far lower emissions from intensified systems with continuous aeration4. We therefore propose that greater adoption of aerated systems is urgently required to address globally significant rises in CH4 emissions from the conversion of paddy fields to aquaculture. China dominates the global growth in aquaculture food production, primarily through massive conversion of paddy fields to crab ponds. This land conversion is greatly increasing methane emissions but these can be significantly reduced by water aeration.

Although microorganisms are the very first colonizers of recently deglaciated soils even prior to plant colonization, the drivers and patterns of microbial community succession at early-successional stages remain poorly understood. The successional dynamics and assembly processes of bacterial and fungal communities were compared on a glacier foreland in the maritime Antarctic across the ~10-year soil-age gradient from bare soil to sparsely vegetated area. Bacterial communities shifted more rapidly than fungal communities in response to glacial retreat; species turnover (primarily the transition from glacier- to soil-favouring taxa) contributed greatly to bacterial beta diversity, but this pattern was less clear in fungi. Bacterial communities underwent more predictable (more deterministic) changes along the soil-age gradient, with compositional changes paralleling the direction of changes in soil physicochemical properties following deglaciation. In contrast, the compositional shift in fungal communities was less associated with changes in deglaciation-induced changes in soil geochemistry and most fungal taxa displayed mosaic abundance distribution across the landscape, suggesting that the successional dynamics of fungal communities are largely governed by stochastic processes. A co-occurrence network analysis revealed that biotic interactions between bacteria and fungi are very weak in early succession. Taken together, these results collectively suggest that bacterial and fungal communities in recently deglaciated soils are largely decoupled from each other during succession and exert very divergent trajectories of succession and assembly under different selective forces.

Terrestrial ecosystems are typically nitrogen (N) limited, but recent years have witnessed N enrichment in various soil ecosystems caused by human activities such as fossil fuel combustion and fertilizer application. This enrichment may alter microbial processes in soils in a way that would increase the emissions of methane (CH

Northern peatlands are substantial carbon sinks because organic matter in peat is highly stable due to the low rate of decomposition. Waterlogged anaerobic conditions induce accumulation of Sphagnum-derived phenolic compounds that inhibit peat organic matter decomposition, a mechanism referred to as the “enzymic latch”. Recent studies have predicted that the water table in northern peatlands may become unstable. We observed that such unstable water table levels can impede the development of Sphagnum mosses. In this study, we determined the effects of low and high frequency water table fluctuation regimes on Sphagnum growth and peat organic matter decomposition, by conducting a year-long mesocosm experiment. In addition, we conducted a molecular analysis to examine changes in abundance of fungal community which may play a key role in the decomposition of organic matter in peatlands. We found that rapid water table fluctuation inhibited the growth of Sphagnum due to fungal infection but stimulated decomposition of organic matter that may dramatically destabilize peatland carbon storage. Increased pH, induced by the fluctuation, may contribute to the enhanced activity of hydrolases in peat. We demonstrated that the water table fluctuation in peatlands impeded Sphagnum growth and accelerates decomposition due to fungal proliferation. Thus, we suggested that understanding the microbial community in the northern peatlands is essential for elucidating the possible changes in carbon cycle of peatland under the changing world.

Invasion of Spartina spp. in tidal salt marshes may affect the function and characteristics of the ecosystem. Previous studies reported that the invasion alters biogeochemical and microbial processes in marsh ecosystems, yet our knowledge of changing archaeal community due to the invasion is still limited, whereas archaeal communities play a pivotal role in biogeochemical cycles within highly reduced marsh soils. In this study, we aimed to illustrate the influences of the Spartina anglica invasion on soil archaeal community and the depth profile of the influences. The relative abundance of archaeal phyla demonstrated that the invasion substantially shifted the characteristics of tidal salt marsh from marine to terrestrial soil only in surface layer, while the influences indirectly propagated to the deeper soil layer. In particular, two archaeal phyla, Asgardaeota and Diapherotrites, were strongly influenced by the invasion, indicating a shift from marine to terrestrial archaeal communities. The shifts in soil characteristics spread to the deeper soil layer that results in indirect propagation of the influences of the invasion down to the deeper soil, which was underestimated in previous studies. The changes in the concentration of dissolved organic carbon and salinity were the substantial regulating factors for that. Therefore, changes in biogeochemical and microbial characteristics in the deep soil layer, which is below the root zone of the invasive plant, should be accounted for a more accurate illustration of the consequences of the invasion.

In Arctic soils, warming accelerates decomposition of organic matter and increases emission of greenhouse gases (GHGs), contributing to a positive feedback to climate change. Although microorganisms play a key role in the processes between decomposition of organic matter and GHGs emission, the effects of warming on temporal responses of microbial activity are still elusive. In this study, treatments of warming and precipitation were conducted from 2012 to 2018 in Cambridge Bay, Canada. Soils of organic and mineral layers were collected monthly from June to September in 2018 and analyzed for extracellular enzyme activities and bacterial community structures. The activity of hydrolases was the highest in June and decreased thereafter over summer in both organic and mineral layers. Bacterial community structures changed gradually over summer, and the responses were distinct depending on soil layers and environmental factors; water content and soil temperature affected the shift of bacterial community structures in both layers, whereas bacterial abundance, dissolved organic carbon, and inorganic nitrogen did so in the organic layer only. The activity of hydrolases and bacterial community structures did not differ significantly among treatments but among months. Our results demonstrate that temporal variations may control extracellular enzyme activities and microbial community structure rather than the small effect of warming over a long period in high Arctic soil. Although the effects of the treatments on microbial activity were minor, our study provides insight that microbial activity may increase due to an increase in carbon availability, if the growing season is prolonged in the Arctic.

BackgroundAmbrosia trifidais a highly invasive annual plant, but effective control methods have not been proposed. Among various eradication methods, cutting is a simple measure to control invasive plants, and sowing seeds of native plants may effectively increase biotic resistance to invasion. In this study, we conducted a field experiment with two treatments: cutting and sowing seeds of six native or naturalized plants.ResultsWe found a significantly lowerA. trifidaabundance after cutting than in the control (77% decrease). Sowing seeds of native species did not provide any additional benefit for the control ofA. trifida, but increased the importance values and diversity of other native vegetation. The abundance ofA. trifidawas negatively correlated with that of other plant taxa based on plant cover, biomass, and density. However, biotic resistance of sown plants was not effective to control invasion becauseA. trifidawas so competitive.ConclusionsWe concluded that cutting is an effective measure to controlAmbrosia trifidawhile sowing seeds of native plants can increase native plant diversity.

Mangrove forests cover only 0.1% of the world's continental area; however, these are a substantial carbon sink owing to the high primary production and low rate of decomposition of soil organic matter (SOM). The extremely low decomposition rate of SOM in mangrove forests is believed to be caused by low oxygen and nutrient availability as well as recalcitrant biomass from mangrove. However, only a few studies have addressed the microbial mechanism that plays a key role in the decomposition of SOM. In this study, the decomposition of SOM were determined by conducting a field survey and an lab incubation experiment using soil samples from mangrove forests in three regions; Okinawa, Shenzhen, and Hong Kong. In particular, we examined the occurrence of the enzymic latch mechanism, which involves phenolic inhibition of enzymic decomposition, in mangrove forest soils that highlights the importance of phenol oxidase as a key controlling factor. The results clearly showed that enzymic latch involved in the accumulation of SOM in the mangroves of Shenzhen and Hong Kong, whereas the accumulation of SOM in Okinawa was controlled by other mechanisms, such as the iron gate mechanism, which involves stabilization of soil carbon in iron-SOM complexes. The characteristics of mangrove forests, such as iron concentration, were shown as substantial determination factors in the dynamics of SOM. We concluded that the decomposition of SOM were strongly affected by the characteristics of mangrove forests, and the occurrence of enzymic latch in mangrove forests has a potential application in geoengineering technology to enhance the carbon sequestration capacity of mangrove forests.

Additional file 1: Table S1. List of species found in the experimental plots.