Methanogenic Community, CH4 Production Potential and Its Determinants in the Active Layer and Permafrost Deposits on the Tibetan Plateau

Weakened priming effect along soil profile in alpine grasslands on the Tibetan Plateau

Subsoils hold a substantial reservoir of organic carbon (C), and its dynamics can be greatly influenced by fresh C inputs through priming effect, potentially altering the magnitude of soil C-climate feedback. Despite the importance of soil C dynamics in regulating this feedback, our understanding of how soil C release and the priming effect vary along the soil profile remains limited, especially in alpine grasslands on the Tibetan Plateau. In particular, the relative importance of abiotic and biotic factors, such as soil physicochemical properties, aggregate and mineral protection, substrate quantity and quality, and plant and microbial properties (e.g., microbial biomass and diversity), in mediating vertical variations in soil C release and the priming effect is still unclear. Using 1-meter-deep soil profiles from five sites on the plateau, our 13C isotope labeling incubation experiments revealed a significant decline in both C release and the priming effect with increasing soil depth. We found that variations in soil C release along the profile were primarily influenced by soil properties (soil moisture and pH), mineral protection (the molar ratios of amorphous Fe/Al oxides to soil organic C (SOC) and soil mineral specific surface area), and hydrolase activity. In addition, vertical variations in the priming effect were dominantly affected by soil properties (soil moisture and pH), mineral and aggregate protection (the molar ratio of exchangeable Ca to SOC and the proportion of C occluded in clay+silt fractions), and microbial properties (oxidase activity and the copy number of bacterial ribosomal RNA gene operons). These findings provide valuable insights into the complex soil C cycling across profiles and its feedback to climate change.

Use of biochar derived from Spartina alterniflora to reduce sediment methane (CH4) production potential during non-farming period in earthen aquaculture ponds

Biochar has been proposed as an effective material for mitigating greenhouse gas emissions from farmlands, but comparable information for earthen aquaculture ponds is limited. A field study was conducted to investigate the effects of adding biochar (200-1600 kg ha-1) derived from the invasive plant Spartina alterniflora on sediment physico-chemical properties, CH4 production potential (PCH4), and the relevant functional gene abundances in earthen aquaculture ponds during the non-farming period. The results indicated that biochar treatments increased sediment porosity and salinity, while decreasing dissolved organic carbon and microbial biomass carbon. Biochar-treated sediments also exhibited a significantly lower abundance of mcrA gene especially in the early drainage stage, and a higher abundance of pmoA gene especially in the intermediate and final drainage stages. Consequently, the mean PCH4 in biochar-treated sediments (1.28-21.12 ng g-1 d-1) was 57-73% lower than in the control group (5.41-39.45 ng g-1 d-1). The reduction in PCH4 did not differ between biochar produced at 300 °C vs. 500 °C and was not dependent on the amount of biochar added. The findings suggest that using biochar derived from S. alterniflora can be a cost-effective method to control the spread of this invasive plant and reduce CH4 production in aquaculture pond sediment during the non-farming period.

Methanogens and what they tell us about how life might survive on Mars

Space exploration and research are uncovering the potential for terrestrial life to survive in outer space, as well as the environmental factors that affect life during interplanetary transfer. The presence of methane in the Martian atmosphere suggests the possibility of methanogens, either extant or extinct, on Mars. Understanding how methanogens survive and adapt under space-exposed conditions is crucial for understanding the implications of extraterrestrial life. In this article, we discuss methanogens as model organisms for obtaining energy transducers and producing methane in a simulated Martian environment. We also explore the chemical evolution of cellular composition and growth maintenance to support survival in extraterrestrial environments. Neutral selective pressure is imposed on the chemical composition of cellular components to increase cell survival and reduce growth under physiological conditions. Energy limitation is an evolutionary driver of macromolecular polymerization, growth maintenance, and survival fitness of methanogens. Methanogens grown in a Martian environment may exhibit global alterations in their metabolic function and gene expression at the system scale. A space systems biology approach would further elucidate molecular survival mechanisms and adaptation to a drastic outer space environment. Therefore, identifying a genetically stable methanogenic community is essential for biomethane production from waste recycling to achieve sustainable space-life support functions.

Comparative analysis of prokaryotic microbiomes in high-altitude active layer soils: insights from Ladakh and global analogues using In-Silico approaches

The active layer is the portion of soil overlaying the permafrost that freezes and thaws seasonally. It is a harsh habitat in which a varied and vigorous microbial population thrives. The high-altitude active layer soil in northern India is a unique and important cryo-ecosystem. However, its microbiology remains largely unexplored. It represents a unique reservoir for microbial communities with adaptability to harsh environmental conditions. In the Changthang region of Ladakh, the Tsokar area is a high-altitude permafrost-affected area situated in the southern part of Ladakh, at a height of 4530 m above sea level. Results of the comparison study with the QTP, Himalayan, Alaskan, Russian, Canadian and Polar active layers showed that the alpha diversity was significantly higher in the Ladakh and QTP active layers as the environmental condition of both the sites were similar. Moreover, the sampling site in the Ladakh region was in a thawing condition at the time of sampling which possibly provided nutrients and access to alternative nitrogen and carbon sources to the microorganisms thriving in it. Analysis of the samples suggested that the geochemical parameters and environmental conditions shape the microbial alpha diversity and community composition. Further analysis revealed that the cold-adapted methanogens were present in the Ladakh, Himalayan, Polar and Alaskan samples and absent in QTP, Russian and Canadian active layer samples. These methanogens could produce methane at slow rates in the active layer soils that could increase the atmospheric temperature owing to climate change.

Permafrost carbon cycle and its dynamics on the Tibetan Plateau

Our knowledge on permafrost carbon (C) cycle is crucial for understanding its feedback to climate warming and developing nature-based solutions for mitigating climate change. To understand the characteristics of permafrost C cycle on the Tibetan Plateau, the largest alpine permafrost region around the world, we summarized recent advances including the stocks and fluxes of permafrost C and their responses to thawing, and depicted permafrost C dynamics within this century. We find that this alpine permafrost region stores approximately 14.1 Pg (1 Pg=1015 g) of soil organic C (SOC) in the top 3 m. Both substantial gaseous emissions and lateral C transport occur across this permafrost region. Moreover, the mobilization of frozen C is expedited by permafrost thaw, especially by the formation of thermokarst landscapes, which could release significant amounts of C into the atmosphere and surrounding water bodies. This alpine permafrost region nevertheless remains an important C sink, and its capacity to sequester C will continue to increase by 2100. For future perspectives, we would suggest developing long-term in situ observation networks of C stocks and fluxes with improved temporal and spatial coverage, and exploring the mechanisms underlying the response of ecosystem C cycle to permafrost thaw. In addition, it is essential to improve the projection of permafrost C dynamics through in-depth model-data fusion on the Tibetan Plateau.

Cadmium reduced methane emissions by stimulating methane oxidation in paddy soils

Flooded rice paddy fields are a significant source of anthropogenic methane (CH4) emissions. Cadmium (Cd) is one of the most common and toxic contaminants in paddy soils. However, little is known about how the soil microbial communities associated with CH4 emissions respond to the increasing Cd-stress in paddies. In this study, we employed isotopically 13C-labelled CH4, high-throughput sequencing analysis, and gene quantification analysis to reveal the effect and mechanism of Cd on CH4 emissions in paddy soils. Results showed that 4.0 mg kg-1 Cd addition reduced CH4 emissions by 16-99% in the four tested paddy soils, and significantly promoted the transformation of 13CH4 to 13CO2. Quantitative polymerase chain reaction (qPCR) demonstrated that Cd addition increased the abundances of pmoA gene, the ratios of methanogens to methanotrophs (mcrA/pmoA) showed a positive correlation with CH4 emissions (R2 = 0.798, p < 0.01). Furthermore, the composition of the microbial community containing the pmoA gene was barely affected by Cd addition (p > 0.05). This observation was consistent with the findings of a pure incubation experiment where methanotrophs exhibited high tolerance to Cd. We argue that microbial feedback to Cd stress amplifies the contribution of methanotrophs to CH4 oxidation in rice fields through the complex interactions occurring among soil microbes. Our study highlights the overlooked association between Cd and CH4 dynamics, offering a better understanding of the role of rice paddies in global CH4 cycling.

Coupling of soil methane emissions at different depths under typical coastal wetland vegetation types

As an important source of atmospheric methane, methane emissions from coastal wetlands are affected by many factors. However, the methane emission process and interrelated coupling mechanisms in coastal wetland soils of a variety of environments remain unclear owing to complex interactions between intensified anthropogenic activities and climate change in recent years. In this study, we investigated methane cycling processes and the response mechanisms of environmental and microbial factors in soils at different depths under four typical coastal wetland vegetation types of the Yellow River Delta, China, using laboratory culture and molecular biology techniques. Our results show that methane generation pathways differed among the different soil layers, and that the methane emission process has a special response to soil N compounds (NO3-, NH4+). We found that nitrogen can indirectly affect methane emission by impacting key physicochemical properties (pH, oxidation reduction potential, etc.) and some functional communities (mcrA, ANME-2d, sulfate-reducing bacteria (SRB), narG, nosZII). Methane production processes in shallow soils compete closely with sulfate reduction processes, while methane emissions facilitated in deeper soils due to denitrification processes. We believe that our results provide a reference for future research and wetland management practices that seek to mitigate the global greenhouse effect and climate change.

Achieving high yield and nitrogen agronomic efficiency by coupling wheat varieties with soil fertility

Wheat breeding has progressively increased yield potential through decades of selection, markedly increased the capacity for food production. Nitrogen (N) fertilizer is essential for wheat production and N agronomic efficiency (NAE) is commonly index used for evaluate the effects of N fertilizer on crop yield, calculated as the difference of wheat yield between N fertilizer treatment and non-N fertilizer treatment divided by the total N application rate. However, the impact of variety on NAE and its interaction with soil fertility remain unknown. Here, to clarify whether and how wheat variety contributes to NAE, and to determine if soil conditions should be considered in variety selection, we conduct a large-scale analysis of data from 12,925 field trials spanning ten years and including 229 wheat varieties, 5 N fertilizer treatments, and a range of soil fertility across China's major wheat production zones. The national average NAE was 9.57 kg kg^-1, but significantly differed across regions. At both the national and regional scales, variety significantly affected NAE, and different varieties showed high variability in their performance among low, moderate, and high fertility soils. Here, superior varieties with both high yield and high NAE were identified at each soil fertility fields. The comprehensive effect of selecting regionally superior varieties, optimizing N management, and improving soil fertility could potentially decrease the yield gap by 67 %. Therefore, variety selection based on soil conditions could facilitate improved food security while reducing fertilizer inputs to alleviate environmental impacts.

Soil organic carbon regulates CH4 production through methanogenic evenness and available phosphorus under different straw managements

Methane (CH₄) is the main greenhouse gas emitted from rice paddy fields driven by methanogens, for which methanogenic abundance on CH₄ production has been intensively investigated. However, information is limited about the relationship between methanogenic diversity (e.g., richness and evenness) and CH₄ production. Three independent field experiments with different straw managements including returning method, burial depth, and burial amount were used to identify the effects of methanogenic diversity on CH₄ production, and its regulating factors from soil properties in a rice-wheat cropping system. The results showed that methanogenic evenness (dominance) can explain 23% of variations in CH₄ production potential. CH₄ production potential was positively related to methanogenic evenness (R² = 0.310, p < 0.001), which is driven by soil organic carbon (SOC), available phosphorus (AP), and nitrate (NO₃^-) through structure equation model (SEM). These findings indicate that methanogenic evenness has a critical role in evaluating the responses of CH₄ production to agricultural practices following changes in soil properties. The SEM also revealed that SOC concentration influenced CH₄ production potential indirectly via complementarity of methanogenic evenness (dominance) and available phosphorus (AP). Increasing SOC accumulation improved AP release and stimulated CH₄ production when SOC was at a low level, whereas decreased evenness and suppressed CH₄ production when SOC was at a high level. A nonlinear relationship was detected between SOC and CH₄ production potential, and CH₄ production potential decreased when SOC was ≥14.16 g kg^-1. Our results indicated that the higher SOC sequestration can not only mitigate CO₂ emissions directly but CH₄ emissions indirectly, highlighting the importance to enhance SOC sequestration using optimum agricultural practices in a rice-wheat cropping system.

Precipitation increase counteracts warming effects on plant and soil C:N:P stoichiometry in an alpine meadow

Temperature and precipitation are expected to increase in the forthcoming decades in the northeastern Qinghai-Tibetan Plateau, with uncertain effects of their interaction on plant and soil carbon:nitrogen:phosphorus (C:N:P) stoichiometry in alpine ecosystems. A two-year field experiment was conducted to examine the effects of warming, precipitation increase, and their interaction on soil and plant C:N:P stoichiometry at functional groups and community level in an alpine meadow. Warming increased aboveground biomass of legumes and N:P ratios of grasses and community, but did not affect soil C:N:P stoichiometry. The piecewise structural equation model (SEM) indicated that the positive effect of warming on community N:P ratio was mainly resulted from its positive influence on the aboveground biomass of functional groups. Precipitation increase reduced C:N ratios of soil, grasses, and community, indicating the alleviation in soil N-limitation and the reduction in N use efficiency of plant. SEM also demonstrated the decisive role of grasses C:N:P stoichiometry on the response of community C:N:P stoichiometry to precipitation increase. The interaction of warming and precipitation increase did not alter plant community and soil, N:P and C:P ratios, which was resulting from their antagonistic effects. The stable soil and plant community C:N:P stoichiometry raised important implications that the effect of warming was offset by precipitation increase. Our study highlights the importance of considering the interaction between warming and precipitation increase when predicting the impacts of climate change on biogeochemical cycles in alpine meadow ecosystems.

Large increase in CH4 emission following conversion of coastal marsh to aquaculture ponds caused by changing gas transport pathways

Methane emissions from aquatic ecosystems play an important role in global carbon cycle and climate change. Reclamation of coastal wetlands for aquaculture use has been shown to have opposite effects on sediment CH₄ production potential and CH₄ emission flux, but the underlying mechanism remained unclear. In this study, we compared sediment properties, CH₄ production potential, emission flux, and CH₄ transport pathways between a brackish marsh and the nearby reclaimed aquaculture ponds in the Min River Estuary in southeastern China. Despite that the sediment CH₄ production potential in the ponds was significantly lower than the marsh, CH₄ emission flux in the ponds (17.4 ± 2.7 mg m^-2 h^-1) was 11.9 times higher than the marsh (1.3 ±  0.2 mg m^-2 h^-1). Plant-mediated transport accounted for 75% of the total CH₄ emission in the marsh, whereas ebullition accounted for 95% of the total CH₄ emission in the ponds. CH₄ emission fluxes in both habitat types were highest in the summer. These results suggest that the increase in CH₄ emission following the conversion of brackish marsh to aquaculture ponds was not caused by increased sediment CH₄ production, but rather by eliminating rhizospheric oxidation and shifting the major transport pathway to ebullition, allowing sediment CH₄ to bypass oxidative loss. This study improves our understanding of the impacts of modification of coastal wetlands on greenhouse gas dynamics.

Changes in sediment methanogenic archaea community structure and methane production potential following conversion of coastal marsh to aquaculture ponds

Widespread conversion of coastal wetlands into aquaculture ponds in coastal region often results in degradation of the wetland ecosystems, but its effects on sediment's potential to produce greenhouse gases remain unclear. Using field sampling, incubation experiments and molecular analysis, we studied the sediment CH₄ production potential and the relevant microbial communities in a brackish marsh and the nearby aquaculture ponds in the Min River Estuary in southeastern China. Sediment CH₄ production potential was higher in the summer and autumn months than in spring and winter months, and it was significantly correlated with sediment carbon content among all environmental variables. The mean sediment CH₄ production potential in the aquaculture ponds (20.1 ng g^-1 d^-1) was significantly lower than that in the marsh (45.2 ng g^-1 d^-1). While Methanobacterium dominated in both habitats (41-59%), the overall composition of sediment methanogenic archaea communities differed significantly between the two habitats (p < 0.05) and methanogenic archaea alpha diversity was lower in the aquaculture ponds (p < 0.01). Network analysis revealed that interactions between sediment methanogenic archaea were much weaker in the ponds than in the marsh. Overall, these findings suggest that conversion of marsh land to aquaculture ponds significantly altered the sediment methanogenic archaea community structure and diversity and lowered the sediment's capacity to produce CH₄.