Not all soil carbon is created equal: Labile and stable pools under nitrogen input.

Anthropogenic activities have raised nitrogen (N) input worldwide with profound implications for soil carbon (C) cycling in ecosystems. The specific impacts of N input on soil organic matter (SOM) pools differing in microbial availability remain debatable. For the first time, we used a much-improved approach by effectively combining the 13C natural abundance in SOM with 21 years of C3-C4 vegetation conversion and long-term incubation. This allows to distinguish the impact of N input on SOM pools with various turnover times. We found that N input reduced the mineralization of all SOM pools, with labile pools having greater sensitivity to N than stable ones. The suppression in SOM mineralization was notably higher in the very labile pool (18%-52%) than the labile and stable (11%-47%) and the very stable pool (3%-21%) compared to that in the unfertilized control soil. The very labile C pool made a strong contribution (up to 60%) to total CO2 release and also contributed to 74%-96% of suppressed CO2 with N input. This suppression of SOM mineralization by N was initially attributed to the decreased microbial biomass and soil functions. Over the long-term, the shift in bacterial community toward Proteobacteria and reduction in functional genes for labile C degradation were the primary drivers. In conclusion, the higher the availability of the SOM pools, the stronger the suppression of their mineralization by N input. Labile SOM pools are highly sensitive to N availability and may hold a greater potential for C sequestration under N input at global scale.

Spatiotemporal dynamic of rice production and its carbon footprint in Hainan, China: Implications for food security and environmental sustainability.

Rice (Oryza sativa L.) feeds more than half of the global population and faces the critical issues related to food security and environmental sustainability. This study analyzed double rice production data from 2010 to 2020 to assess its spatiotemporal dynamic in food production and carbon (C) footprint in Hainan province, China. The results revealed a 29.5% reduction in rice planting area, leading to a significantly decreased rice self-sufficiency rate from 38% to 33% from 2010 to 2020. During this period, the carbon footprint per unit area (CFa) for early, late, and double rice showed a fluctuating upward trend ranging from 8.1 to 8.4, 8.9 to 9.2, and 17.0 to 17.4 t CO2-eq ha-1, respectively. The total greenhouse gas (GHG) emissions of rice production decreased to around 2 million t CO2-eq, primarily due to reduced planting area. The C sequestration initially increased before decreasing to 1.2 million t C in 2020 at a temporal scale. Spatially, the northeast and southwest regions exhibited ∼70% of the total GHG emissions and ∼80% of C sequestration. The regional C footprint per unit yield displayed less favorable outcomes, with some areas (e.g., Wenchang and Haikou) experiencing emission hotspots in recent years. Higher yield and smaller CFa for Lingao and Tunchang were observed compared to the average between 2010 and 2020. This study provides insights into the spatiotemporal dynamics of double rice production and GHG emissions in Hainan, offering a scientific reference for regional food security and environmental sustainability.

Soybean inclusion reduces soil organic matter mineralization despite increasing its temperature sensitivity.

Legume-based cropping increased the diversity of residues and rhizodeposition input into the soil, thus affecting soil organic matter (SOM) stabilization. Despite this, a comprehensive understanding of the mechanisms governing SOM mineralization and its temperature sensitivity across bulk soil and aggregate scales concerning legume inclusion remains incomplete. Here, a 6-year field experiment was conducted to investigate the effects of three cropping systems (i.e., winter wheat/summer maize, winter wheat/summer maize-soybean, and nature fallow) on SOM mineralization, its temperature sensitivity, and the main drivers in both topsoil (0-20 cm) and subsoil (20-40 cm). Soybean inclusion decreased the SOM mineralization by 17%-24%, while concurrently increasing the majority of soil biochemical properties, such as carbon (C) acquisition enzyme activities (5%-22%) and microbial biomass C (5%-9%), within the topsoil regardless of temperature. This is attributed to the increased substrate availability (e.g., dissolved organic C) facilitating microbial utilization, thus devoting less energy to mining nutrients under diversified cropping. In addition, SOM mineralization was lower within macroaggregates (∼12%), largely driven by substrate availability irrespective of aggregate sizes. In contrast, diversified cropping amplified the Q10 of SOM mineralization in mesoaggregates (+6%) and microaggregates (+5%) rather than in macroaggregates. This underscores the pivotal role of mesoaggregates and microaggregates in dominating the Q10 of SOM mineralization under soybean-based cropping. In conclusion, legume-based cropping diminishes soil organic matter mineralization despite increasing its temperature sensitivity, which proposes a potential strategy for C-neutral agriculture and climate warming mitigation.

Short-term continuous monocropping reduces peanut yield mainly via altering soil enzyme activity and fungal community.

Continuous monocropping can lead to soil sickness and increase of soil-borne disease, which finally reduces crop yield. Microorganisms benefit plants by increasing nutrient availability, participating in auxin synthesis, and defending against pathogens. However, little is known about the influence of short-term successive peanuts cropping on soil properties, enzyme activities, its yield, plant-associated microbes, and their potential correlations in peanut production. Here, we examined the community structure, composition, network structure and function of microbes in the rhizosphere and bulk soils under different monocropping years. Moreover, we assessed the impact of changes in the soil micro-environment and associated soil microbes on peanut yield. Our results showed that increase of monocropping year significantly decreased most soil properties, enzyme activities and peanut yield (p < 0.05). Principal co-ordinates analysis (PCoA) and analysis of similarities (ANOSIM) indicated that monocropping year significantly influenced the fungal community structure in the rhizosphere and bulk soils (p < 0.01), while had no effect on the bacterial community. With the increase of continuous monocropping year, peanut selectively decreased (e.g., Candidatus_Entotheonella, Bacillus and Bryobacter) or increased (e.g., Nitrospira, Nocardioides, Ensifer, Gaiella, and Novosphingobium) the abundance of some beneficial bacterial genera in the rhizosphere. Continuous monocropping significantly increased the abundance of plant pathogens (e.g., Plectosphaerella, Colletotrichum, Lectera, Gibberella, Metarhizium, and Microdochium) in the rhizosphere and negatively affected the balance of fungal community. Besides, these species were correlated negatively with L-leucine aminopeptidase (LAP) activity. Network co-occurrence analysis showed that continuous monocropping simplified the interaction network of bacteria and fungi. Random forest and partial least squares path modeling (PLS-PM) analysis further showed that fungal community, pathogen abundance, soil pH, and LAP activity negatively affected peanut yield. In conclusion, short-term continuous monocropping decreased LAP activity and increased potential fungal pathogens abundance, leading to reduction of peanut yield.

Peanut-based Rotation Stabilized Diazotrophic Communities and Increased Subsequent Wheat Yield.

The introduction of legumes into rotations can improve nitrogen use efficiency and crop yield; however, its microbial mechanism involved remains unclear. This study aimed to explore the temporal impact of peanut introduction on microorganisms related to nitrogen metabolism in rotation systems. In this study, the dynamics of diazotrophic communities in two crop seasons and wheat yields of two rotation systems: winter wheat - summer maize (WM) and spring peanut → winter wheat - summer maize (PWM) in the North China Plain were investigated. Our results showed that peanut introduction increased wheat yield and biomass by 11.6% (p < 0.05) and 8.9%, respectively. Lower Chao1 and Shannon indexes of the diazotrophic communities were detected in soils that sampling in June compared with those sampling in September, although no difference was found between WM and PWM. Principal co-ordinates analysis (PCoA) showed that rotation system significantly changed the diazotrophic community structures (PERMANOVA; p < 0.05). Compared with WM, the genera of Azotobacter, Skermanella, Azohydromonas, Rhodomicrobium, Azospirillum, Unclassified_f_Opitutaceae, and Unclassified_f_Rhodospirillaceae were significantly enriched (p < 0.05) in PWM. Furthermore, rotation system and sampling time significantly influenced soil properties, which significantly correlated with the top 15 genera in relative abundance. Partial least squares path modeling (PLS-PM) analysis further showed that the diazotrophic community diversity (alpha- and beta-diversity) and soil properties (pH, SOC and TN) significantly affected wheat yield. In conclusion, legume inclusion has the potential to stabilize diazotrophic community structure at the temporal scales and increase subsequent crop yield.

Plant growth stages covered the legacy effect of rotation systems on microbial community structure and function in wheat rhizosphere.

Legume-based crop rotation is conducive to improve soil multifunctionality, but how the legacy effect of previous legumes influenced the rhizosphere  microbial community of the following crops along with growth stages remains unclear. Here, the wheat rhizosphere microbial community was assessed at the regreening and filling stages with four previous legumes (mungbean, adzuki bean, soybean, and peanut), as well as cereal maize as a control. The composition and structure of both bacterial and fungal communities varied dramatically between two growth stages. The differences in fungal community structure among rotation systems were observed at both the regreening and filling stages, while the difference in bacterial community structure among rotation systems was observed only at the filling stage. The complexity and centrality of the microbial network decreased along with crop growth stages. The species associations were strengthened in legume-based rotation systems than in cereal-based rotation system at the filling stage. The abundance of KEGG orthologs (KOs) associated with carbon, nitrogen, phosphorus, and sulfur metabolism of bacterial community decreased from the regreening stage to the filling stage. However, there was no difference in the abundance of KOs among rotation systems. Together, our results showed that plant growth stages had a stronger impact than the legacy effect of rotation systems in shaping the wheat rhizosphere microbial community, and the differences among rotation systems were more obvious at the late growth stage. Such compositional, structural, and functional changes may provide predictable consequences of crop growth and soil nutrient cycling.

Replacing chemical fertilizer with manure reduces N2O emissions in winter wheat - summer maize cropping system under limited irrigation.

Nitrous oxide (N2O) emissions from agroecosystems are a major contributor to global warming and stratospheric ozone depletion. However, knowledge concerning the hotspots and hot moments of soil N2O emissions with manure application and irrigation, as well as the underlying mechanisms remain incomplete. Here, a 3-year field experiment was conducted with the combination of fertilization (no fertilizer, F0; 100% chemical fertilizer N, Fc; 50% chemical N + 50% manure N, Fc + m; and 100% manure N, Fm) and irrigation (with irrigation, W1; and without irrigation, W0; at wheat jointing stage) for winter wheat - summer maize cropping system in the North China Plain. Results showed that irrigation did not affect annual N2O emissions of the wheat-maize system. Manure application (Fc + m and Fm) reduced annual N2O emissions by 25-51% compared with Fc, which mainly occurred during 2 weeks after fertilization combined with irrigation (or heavy rainfall). In particular, Fc + m reduced the cumulative N2O emissions during 2 weeks after winter wheat sowing and summer maize top dressing by 0.28 and 0.11 kg ha-1, respectively, compared with Fc. Meanwhile, Fm maintained the grain N yield and Fc + m increased grain N yield by 8% compared with Fc under W1. Overall, Fm maintained the annual grain N yield and lower N2O emissions compared to Fc under W0, and Fc + m increased the annual grain N yield and maintained N2O emissions compared with Fc under W1, respectively. Our results provide scientific support for using manure to minimize N2O emissions while maintaining crop N yield under optimal irrigation to support the green transition in agricultural production.

The long-term uncertainty of biodegradable mulch film residues and associated microplastics pollution on plant-soil health.

Biodegradable mulch film potentially offers an encouraging alternative to conventional (petroleum-based) plastic films. Since biodegradable films are more susceptible to rapid degradation, more microplastics (MPs) are likely to be generated than conventional films within the same time frame, probably leading to more severe MPs pollution and associated effects. However, the effect of biodegradable mulch film residues and associated MPs pollution on plant-soil health remains uncertainty. Here, we evaluated the potential effect of bio-MPs pollution on soil carbon (C) and nutrient (i.e., N and P) cycling, soil biology (microorganisms and mesofauna), and plant health, as these are crucial to agroecosystem functioning and the delivery of key ecosystem services. Unlike the inert (and therefore recalcitrant) C contained within petroleum-based MPs, at least 80% of the C from bio-MPs is converted to CO2, with up to 20% immobilized in living microbial biomass (i.e., < 0.05 t C ha-1). Although biodegradable films are unlikely to be important in promoting soil C storage, they may accelerate microbial biomass turnover in the short term, as well as CO2 production. Compared to conventional MPs, bio-MPs degradation is more pronounced, thereby inducing greater alterations in microbial diversity and community composition. This may further alter N2O and CH4 emissions, and ultimately resulting in unpredictable consequences for global climate warming. The extent to which this may occur, however, has yet to be shown in either laboratory or field studies. In addition, bio-MPs have a large chance of forming nanoplastics, potentially causing a stronger toxic effect on plants relative to conventional MPs. Consequently, this would influence plant health, crop productivity, and food safety, leading to potential health risks. It is unclear, however, if these are direct effects on key plant processes (e.g. signaling, cell expansion) or indirect effects (e.g. nutrient deficiency or acidification). Overall, the question as to whether biodegradable mulch films offer a promising alternative to solve the conventional plastic legacy in soil over the long term remains unclear.

Field application of biodegradable microplastics has no significant effect on plant and soil health in the short term.

Bioplastics (biodegradable plastics) potentially offer an encouraging alternative to conventional (petroleum-based) plastics. In practice, bioplastics inevitably generate a large number of bio-microplastics (bio-MPs, diameter <5 mm) during the degradation progress. However, the impact of bio-MPs on plant and soil health within agroecosystems remains incomplete. Here, a field study was conducted to investigate the effect of two shapes (fiber and powder) of pure polylactic acid (PLA) bio-MPs on oat (Avena sativa L.) and soybean (Glycinemax (L.) Merr.) growth and soil health. Our results showed that PLA application at a representative soil loading rate of 0.2% (w/w) had no significant effect on soil enzyme activities, soil physicochemical properties (soil water content, pH, etc.), root characteristics, plant biomass, and crop yield. Thus, we conclude that soil quality, plant health, and ecosystem multifunctionality were not affected by PLA over one growing season (5 months) in the presence of either bio-MP shape (fiber and powder) for either crop species (oat and soybean). Overall, PLA based bio-MPs may not pose a significant threat to agroecosystem functions in the short term (days to months) in the field, thus may provide a viable environmentally benign solution to replace traditional non-biodegradable plastics in agroecosystems.

Global systematic review with meta-analysis reveals yield advantage of legume-based rotations and its drivers.

Diversified cropping systems, especially those including legumes, have been proposed to enhance food production with reduced inputs and environmental impacts. However, the impact of legume pre-crops on main crop yield and its drivers has never been systematically investigated in a global context. Here, we synthesize 11,768 yield observations from 462 field experiments comparing legume-based and non-legume cropping systems and show that legumes enhanced main crop yield by 20%. These yield advantages decline with increasing N fertilizer rates and crop diversity of the main cropping system. The yield benefits are consistent among main crops (e.g., rice, wheat, maize) and evident across pedo-climatic regions. Moreover, greater yield advantages (32% vs. 7%) are observed in low- vs. high-yielding environments, suggesting legumes increase crop production with low inputs (e.g., in Africa or organic agriculture). In conclusion, our study suggests that legume-based rotations offer a critical pathway for enhancing global crop production, especially when integrated into low-input and low-diversity agricultural systems.

Soybean Crops Penalize Subsequent Wheat Yield During Drought in the North China Plain.

Contemporary wisdom suggests that inclusion of legumes into crop rotations benefit subsequent cereal crop yields. To investigate whether this maxim was generically scalable, we contrast summer soybean-winter wheat (SW) with summer maize-winter wheat (MW) rotation systems in an extensive field campaign in the North China Plain (NCP). We identify heretofore unseen interactions between crop rotation, synthetic N fertilizer application, and stored soil water. In the year with typical rainfall, inclusion of soybean within rotation had no effect on wheat ear number and yield, while N fertilization penalized wheat yields by 6-8%, mainly due to lower dry matter accumulation after anthesis. In contrast, in dry years prior crops of soybean reduced the rate and number of effective ears in wheat by 5-27 and 14-17%, respectively, leading to 7-23% reduction in wheat yield. Although N fertilization increased the stem number before anthesis in dry years, there was no corresponding increase in ear number and yield of wheat in such years, indicating compensating reduction in yield components. We also showed that N fertilization increased wheat yield in MW rather than SW as the former better facilitated higher dry matter accumulation after flowering in dry years. Taken together, our results suggest that soybean inclusion reduced soil available water for subsequent wheat growth, causing yield penalty of subsequent wheat under drought conditions. We call for more research into factors influencing crop soil water, including initial state, crop water requirement, and seasonal climate forecasts, when considering legumes into rotation systems. Graphical AbstractResponse of wheat population and yield to soybean inclusion under limited-irrigation.

Deep-rooted perennial crops differ in capacity to stabilize C inputs in deep soil layers.

Comprehensive climate change mitigation necessitates soil carbon (C) storage in cultivated terrestrial ecosystems. Deep-rooted perennial crops may help to turn agricultural soils into efficient C sinks, especially in deeper soil layers. Here, we compared C allocation and potential stabilization to 150 cm depth from two functionally distinct deep-rooted perennials, i.e., lucerne (Medicago sativa L.) and intermediate wheatgrass (kernza; Thinopyrum intermedium), representing legume and non-legume crops, respectively. Belowground C input and stabilization was decoupled from nitrogen (N) fertilizer rate in kernza (100 and 200 kg mineral N ha-1), with no direct link between increasing mineral N fertilization, rhizodeposited C, and microbial C stabilization. Further, both crops displayed a high ability to bring C to deeper soil layers and remarkably, the N2-fixing lucerne showed greater potential to induce microbial C stabilization than the non-legume kernza. Lucerne stimulated greater microbial biomass and abundance of N cycling genes in rhizosphere soil, likely linked to greater amino acid rhizodeposition, hence underlining the importance of coupled C and N for microbial C stabilization efficiency. Inclusion of legumes in perennial cropping systems is not only key for improved productivity at low fertilizer N inputs, but also appears critical for enhancing soil C stabilization, in particular in N limited deep subsoils.

Diversified cropping systems benefit soil carbon and nitrogen stocks by increasing aggregate stability: Results of three fractionation methods.

Understanding carbon (C) and nitrogen (N) sequestration in diversified cropping systems provides a pivotal insight for soil health management. Here, the soil was sampled from an ongoing field experiment (five years) with three cropping systems: i) winter wheat/summer maize, ii) winter wheat/summer maize-early soybean, and iii) fallow. We evaluated C and N stocks in aggregates for topsoil (0-20 cm) and subsoil (20-40 cm) depending on cropping systems by comparison of three aggregate fractionation methods (dry, optimal-moisture, and wet sieving). Although the fertilizer application rate for wheat/maize was twice as much as for wheat/maize-soybean, this resulted in similar C and N stocks in the topsoil. The N stock, however, was 13% higher under wheat/maize-soybean than under wheat/maize in the subsoil due to N2 fixation by soybean. The C and N stocks decreased by 22% and 12% under fallow compared to wheat/maize in the topsoil. The wheat/maize-soybean cropping system increased soil aggregates size when estimated by dry and optimal-moisture fractionations. The aggregate size distribution shifted from the dominance of large (> 2 mm) toward small macroaggregates (0.25-2 mm) with increasing moisture used by fractionation due to the low stability of large macroaggregates. Thus, the combination of dry and optimal-moisture sieving is the preferred method to characterize aggregate stability. Overall, diversified cropping systems increase soil aggregation and stability, thus have great potential to enhance soil C and N stocks.

Do cropping system and fertilization rate change water-stable aggregates associated carbon and nitrogen storage?

Soil aggregates not only store carbon (C) and nitrogen (N) but hold a critical role in determining the nutrients supply, crop productivity, and climate change mitigation. However, the impact of cropping system and N fertilization on aggregate-associated C and N in both topsoil and subsoil remains unclear. Here, we assessed the effect of cropping systems (wheat-soybean vs. wheat-maize cropping systems) and N fertilization rates (0 N; medium N, 120 kg N ha-1; high N, 240 kg N ha-1) on soil water-stable aggregates distribution, as well as aggregate-associated C and N based on a field study in North China Plain. Our study suggests that the variations of soil organic carbon (SOC) and total nitrogen (TN) stocks were more affected by N fertilization than short-term cropping systems. In the wheat-soybean system, medium N increased the SOC stock by 19.18% and 15.73% as compared to high N in the topsoil and subsoil, respectively. Additionally, medium N resulted in 6.59-18.11% higher TN stock in the topsoil for both wheat-soybean and wheat-maize cropping systems as compared to 0 N and high N. Notably, the water-stable macroaggregates (> 0.25 mm) in the topsoil occupied more than 70% of the soil, which increased under medium N in the wheat-soybean cropping system. In conclusion, medium N fertilization combined with a legume-based cropping could be used to improve SOC stock, promote soil aggregation, and enhance aggregate-associated C.

Metagenomic insights into soil microbial communities involved in carbon cycling along an elevation climosequences.

Diversity and community composition of soil microorganisms along the elevation climosequences have been widely studied, while the microbial metabolic potential, particularly in regard to carbon (C) cycling, remains unclear. Here, a metagenomic analysis of C related genes along five elevations ranging from 767 to 4190 m at Mount Kilimanjaro was analysed to evaluate the microbial organic C transformation capacities in various ecosystems. The highest gene abundances for decomposition of moderate mineralizable compounds, i.e. carbohydrate esters, chitin and pectin were found at the mid-elevations with hump-shaped pattern, where the genes for decompositions of recalcitrant C (i.e. lignin) and easily mineralizable C (i.e. starch) showed the opposite trend (i.e. U-shaped pattern), due to high soil pH and seasonality in both low and high elevations. Notably, the gene abundances for the decompositions of starch, carbohydrate esters, chitin and lignin had positive relationships with corresponding C compounds, indicating the consistent responses of microbial functional profiles and metabolites to elevation climosequences. Understanding of adaptation of microbial communities, potential function and metabolites to elevation climosequences and their influencing factors provided a new insight for the regulation of terrestrial C storage.

Plant intraspecific competition and growth stage alter carbon and nitrogen mineralization in the rhizosphere.

Plant roots interact with rhizosphere microorganisms to accelerate soil organic matter (SOM) mineralization for nutrient acquisition. Root-mediated changes in SOM mineralization largely depend on root-derived carbon (root-C) input and soil nutrient status. Hence, intraspecific competition over plant development and spatiotemporal variability in the root-C input and nutrients uptake may modify SOM mineralization. To investigate the effect of intraspecific competition on SOM mineralization at three growth stages (heading, flowering, and ripening), we grew maize (C4 plant) under three planting densities on a C3 soil and determined in situ soil C- and N-mineralization by 13 C-natural abundance and 15 N-pool dilution approaches. From heading to ripening, soil C- and N-mineralization rates exhibit similar unimodal trends and were tightly coupled. The C-to-N-mineralization ratio (0.6 to 2.6) increased with N availability, indicating that an increase in N-mineralization with N depletion was driven by microorganisms mining N-rich SOM. With the intraspecific competition, plants increased specific root lengths as an efficient strategy to compete for resources. Root morphologic traits rather than root biomass per se were positively related to C- and N-mineralization. Overall, plant phenology and intraspecific competition controlled the intensity and mechanisms of soil C- and N- mineralization by the adaptation of root traits and nutrient mining.

Combined biochar and nitrogen application stimulates enzyme activity and root plasticity.

Biochar (BC) and nitrogen (N) fertilizers are frequently applied to improve soil properties and increase crop productivity. Nonetheless, our mechanistic understanding of plant-soil interactions under single or combined application of BC and N remains incomplete. For the first time, we applied a split-root system to evaluate how BC or N contributes to the changes in soil enzyme activities, N and phosphorus (P) cycling as well as root plasticity. Left and right parts of rhizoboxes were filled with silty-clay loamy soil amended with BC (15 g kg-1 soil, from wheat straw, 300 °C), N (0.05 g KNO3-N kg-1 soil) or a control (no amendments), resulting in the following combinations: BC/Control, N/Control, BC/N. Soil enzyme activities, available N and P, root morphology and plant biomass were analyzed after plant harvest. Plant biomass (shoot + root) ranged from 0.56 g pot-1 (BC/Control) to 0.91 g pot-1(BC/N). The decreased soil bulk density and increased P availability in the BC compartment (BC/Control and BC/N) stimulated root length by 1.4-1.8 times - an effect that was independent of N availability in the same rhizobox. Biochar stimulated activities of ß-glucosidase and leucine aminopeptidase (by 33-39%) compared to N due to the coupling of C, N and P cycles in BC/N treated soil. Nitrogen fertilization also increased ß-glucosidase activity compared to the unfertilized control, whereas root elongation remained unaffected. Thus, the combined application of BC/N had more efficient benefits for plant growth than BC or N alone. This is linked with i) the stimulation of enzyme activities at the BC locations to reduce N limitation for both microorganisms and plants, and ii) an increase of fine root production to improve N uptake efficiency. Thus, combined BC/N application is potentially especially sustainable to overcome nutrient limitation as well as to maintain crop productivity because it accelerates root-microbial interactions.

Manure amendment increased the abundance of methanogens and methanotrophs but suppressed the type I methanotrophs in rice paddies.

Methane (CH4) emission is the consequence of CH4 production and consumption performed by methanogens and methanotrophs, respectively. Fertilization is an important factor that regulates the behavior of methanogens and methanotrophs; however, the effect of manure and rice straw addition combined with inorganic fertilizers on these communities is not well understood. This study aimed to explore how manure and rice straw amendments together with inorganic fertilizers influenced the methanogenic and methanotrophic communities in a 31-year fertilized rice paddy. Manure amendment significantly increased the abundance of mcrA and pmoA genes by 61.2% and 63.3% compared with the unfertilized control, whereas inorganic NPK fertilization alone or rice straw addition did not affect their abundances. Manure and rice straw amendments greatly decreased the Shannon index and ACE index of the methanogenic communities, whereas inorganic NPK fertilization alone increased the ACE index of the methanotrophic communities compared with the unfertilized control. Methanosarcinaceae and Methylococcaceae dominated at the family level, representing 23.1-35.0% and 48.7-67.2% of the total reads, for the methanogenic and methanotrophic communities, respectively. Application of manure together with inorganic fertilizers suppressed the Methanocellales methanogens and the type I methanotrophs (Methylococcus and Methylobacter). Fertilization greatly altered the community structure of methanogens and methanotrophs, and manure addition had more apparent effects than rice straw. Moreover, total nitrogen, soil organic carbon, available phosphorus, and available potassium correlated significantly to the abundance, composition, and community structure of methanogens and methanotrophs. In conclusion, our study revealed that long-term manure amendment in combination with inorganic fertilizers significantly increased the abundance of methanogens and methanotrophs, but suppressed the type I methanotrophs in rice paddies.

Impact of water table levels and winter cover crops on greenhouse gas emissions from cultivated peat soils.

Drainage and cultivation have turned peatlands from carbon (C) sinks into hotspots for greenhouse gas (GHG) emissions. Raising the water table and planting of winter cover crops are potential strategies to help reduce peat oxidation and re-initiate net C accumulation during the non-cropping period. However, the effects of these practices as well as their interactions on GHG emissions remain unclear. Here, we carried out an outdoor mesocosm experiment to elucidate the effect of water table levels (-30 cm and -50 cm) and winter cover crop cultivation (vetch, rye, no plant) on carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes during the winter period (November-April). Soil-atmosphere GHG exchange, GHG concentrations within the peat profile and soil water solute concentrations were monitored. Our results showed that high water table significantly reduced ecosystem respiration, while it had no net effect on N2O and CH4 fluxes. Uptake of available N by the cover crop significantly reduced nitrate in soil solution, thereby lowering the potential for leaching and both direct and indirect N2O emissions. No interactive effects between water table levels and cover crops were detected for any of the measured GHG fluxes. Seasonal variations of GHG fluxes were positively correlated with soil air concentrations at -15 cm and -40 cm depths, which were further regulated by dissolved organic C, nitrate concentration, and anaerobic conditions in the soil. This study suggests that there is great potential to raise water table levels and introduce green cover crops to reduce GHG emissions. Further studies are needed to achieve a complete evaluation of these strategies outside of the growing season, which may provide a significant mitigation benefit in C-rich cultivated peatlands.

Changes in Fungal Communities across a Forest Disturbance Gradient.

Deforestation has a substantial impact on aboveground biodiversity, but the response of belowground soil fungi remains poorly understood. In a tropical montane rainforest in southwestern China, plots were established along a forest degradation gradient ranging from mature and regenerated forests to open land to examine the impacts of forest degradation and deforestation on ecosystem diversity and function. Here, we evaluated the changes in belowground fungal diversity and community composition using a metabarcoding approach. Soil saprotrophic fungal richness declined with increasing forest disturbance. For example, Penicillium spp. (phosphorus [P]-solubilizing fungi) dominated in mature forest but were less abundant in regenerating forests and showed the lowest abundance in open land sites. Conversely, the abundance of facultative pathogenic fungi increased along the disturbance gradient. The decline in soil saprophytic fungi may be a direct result of forest disturbance or it may be associated with increased availability of soil phosphorus indirectly through an increase in soil pH. The increase in abundance of facultative pathogenic fungi may be related to reduced competition with saprotrophic fungi, changes in microclimate, or increased spore rain. These results demonstrate a loss of dominant P-solubilizing saprotrophic fungi along the disturbance gradient, indicating a change from soil P limitation in mature tropical forests to soil C limitation in deforested sites. The increased prevalence of pathogenic fungi may inhibit plant succession following deforestation. Overall, this research demonstrates that soil fungi can be used as a sensitive indicator for soil health to evaluate the consequences of forest disturbance.IMPORTANCE The soil fungal functional group changes in response to forest disturbance and indicates a close interaction between the aboveground plant community and the belowground soil biological community. Soil saprotrophic fungi declined in relative abundance with increasing forest disturbance. At the same time, the relative abundance of facultative pathogenic fungi increased. The loss of saprotrophic fungal richness and abundance may have been a direct result of forest disturbance or an indirect result of changes in soil pH and soil P. Furthermore, the dominant P-solubilizing saprotrophic fungi were replaced by diverse facultative pathogenic fungi, which have weaker C decomposition ability. These changes potentially indicate a shift from soil phosphate limitation to carbon limitation following deforestation. This study suggests that changes in fungal functional group composition can be used as an indicator of the effects of forest disturbance on soil carbon and nutrients.