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Perennial bioenergy crops accumulate carbon (C) in soils through minimally disturbing management practices and large root inputs, but the mechanisms of microbial control over C dynamics under bioenergy crops have not been clarified. Root‐derived C inputs affect both soil microbial contribution to and degradation of soil organic matter resulting in differing soil organic carbon (SOC) concentrations, storage, and stabilities under different vegetation regimes. Here, we measured biomarker amino sugars and neutral sugars and used diffuse reflectance mid‐infrared Fourier transform spectroscopy (DRIFTS) to explore microbial C contributions, degradation ability, and SOC stability, respectively, under four potential bioenergy crops, M.×giganteus (Miscanthus × giganteus), switchgrass (Panicum virgatum L.), a mixed prairie, and a maize (Zea mays L.)–maize–soybean (Glycine max(L.) Merr.) (MMS) rotation over six growing seasons. Our results showed that SOC concentration (g/kg) increased by 10.6% in mixed prairie over the duration of this experiment and SOC storage (Mg/ha) increased by 17.0% and 15.6% in switchgrass and mixed prairie, respectively. Conversion of row crops to perennial grasses maintained SOC stability and increased bacterial residue contribution to SOC in M.×giganteus and switchgrass by 20.0% and 15.0%, respectively, after 6 years. Degradation of microbe‐derived labile SOC was increased in M.×giganteus, and degradation of both labile and stable SOC increased in MMS rotation. These results demonstrate that microbial communities under perennial grasses maintained SOC quality, while SOC quantity increased under switchgrass and mixed prairie. Annual MMS rotation displayed decreases in aspects of SOC quality without changes in SOC quantity. These findings have implications for understanding microbial control over soil C quantity and quality under land‐use shift from annual to perennial bioenergy cropping systems. Microbial substrate preference is speculated to be driven by labile carbon inputs and available nitrogen. The results from this study demonstrate optimal conditions for increasing soil organic carbon quantity and quality beyond a cessation of tillage include a diverse aboveground ecosystem, high belowground labile carbon inputs, and available nitrogen.

The alpine grasslands account for approximately 54.5% of the total carbon in China’s grasslands, and carbohydrate-active enzymes (CAZymes) play key roles in the turnover of carbon. However, the variation and factors influencing gene-encoding enzymes for plant- and microbial-derived carbon decomposition in alpine steppes and alpine meadows remain unclear. Here, the trends in microbial carbohydrate-active enzymes (CAZymes) and their responses to the decomposition of biomass of different origins were studied using metagenomics in the alpine steppes and alpine meadows on the Tibetan Plateau. Our results revealed the abundance of GTs and CBMs was higher in the alpine steppes than in the alpine meadows, whereas AAs were higher in the alpine steppes than in the alpine meadows. Soil properties (i.e., soil water content, soil ammonium nitrogen, and nitrate nitrogen) highly related to CAZyme genes (GTs, CBMs, and AAs) showed an abundant pattern between the alpine steppes and alpine meadows. Moreover, our results indicated that the relative abundance of genes encoding CAZymes involved in the decomposition of plant- (indicated by cellulose, hemicellulose, and lignin) and fungal-derived carbon (indicated by chitin and glucans) was higher by 8.7% and 10.1%, respectively, in the alpine steppes than in the alpine meadows, whereas bacterial-derived carbon (indicated by peptidoglycan) was lower by 7.9% in the alpine steppes than in the alpine meadows. Soil water content (SWC), nitrate nitrogen (NO3−), and pH influenced on the abundance of CAZyme genes involved in the decomposition of plant-, fungal-, bacterial-derived carbon. In addition, the dominant microbial phyla (Actinobacteria, Protebacteria, and Acidobacteria) mineralized carbon sources from plant- and microbial-derived carbon through their corresponding CAZyme families. In conclusion, our study compared plant- and microbial-derived carbon decomposition potentials and influencing factors to illustrate the contribution of dead biomass to carbon accumulation in alpine grasslands.

Background and aims Priming effect (PE) of soil organic carbon (SOC) decomposition induced by exogenous organic C is an important ecological process in regulating the soil C cycle. The objective of this study was to evaluate how the PE varied among different ecosystems at the global scale and explore factors that drive the direction and magnitude of the PE. Methods Using 2048 experimental comparisons compiled from 94 incubation studies with stable ( 13 C) or radioactive ( 14 C) carbon isotopic techniques, we performed a meta-analysis on the effect of exogenous organic C input on native SOC decomposition (i.e., PE) across multiple terrestrial ecosystems. In particular, the linear mixed-effect model was used to examine the relationship between the PE and potential influencing factors. Results The addition of exogenous organic C significantly enhanced native SOC decomposition by 47.5% (i.e., positive PE), with the highest value in cropland soils (60.9%) and the lowest value in forest soils (26.2%). The intensity of the PE decreased with increasing SOC content, soil total nitrogen content, soil C/N, incubation duration, and incubation temperature, but increased with increasing exogenous organic C addition rate and soil pH. Soil PE was not affected by the complexity of exogenous organic C. Conclusions Our results indicate that positive PE is a widespread phenomenon in terrestrial ecosystems, and that the magnitude is closely related to soil properties and experimental conditions. These findings may be useful for understanding soil C priming and the effect on soil C balance under climate change scenarios.

The response of soil organic carbon (SOC) decomposition to global warming is a potentially major source of uncertainty in climate prediction. However, the magnitude and direction of SOC cycle feedbacks under climate warming remain uncertain because of the knowledge gap about the global‐scale spatial pattern and temperature sensitivity (Q10) mechanism of SOC decomposition. Here, we collected data of Q10 and corresponding soil variables from 81 peer‐reviewed papers using laboratory incubation to explore how Q10 varied among different ecosystems at the global scale and whether labile and recalcitrant SOC pools had equal Q10 values. Q10 with a global average of 2.41 substantially varied among different ecosystems, ranging from the highest in cropland soils (2.76) and the lowest in wetland soils (1.84). Hump‐shaped correlations of Q10 values with the maximum at SOC = 190 g/kg and the minimum at clay = 37% were observed. However, the main influencing factors of Q10 differed among various ecosystems. Q10 values showed a clear decrease with increasing incubation temperature but no significant decrease above 25°C. In general, labile SOC was less sensitive than recalcitrant SOC to warming. Structural equation model analyses showed that total N and SOC accounted for 53% and 46%, respectively, of the variation in Q10 of labile SOC and recalcitrant SOC. This finding suggested that Q10 values of labile and recalcitrant SOC pools had different controlling factors. Our findings highlighted the importance of Q10’s variations in ecosystem types and the response of recalcitrant SOC to warming in predicting the soil C cycling and its feedback to climate change. Therefore, ecosystem type and difference in Q10 of labile and recalcitrant SOC should be considered to precisely predict the soil C dynamics under global warming. A plain language summary is available for this article. Plain Language Summary

Aims The priming effect (PE) on native soil organic matter induced by exogenous carbon addition influences soil carbon and nutrient cycling across the soil depths. Therefore, this study aimed to explore the effects of exogenous glucose-induced PE on native soil organic carbon (SOC) influenced by soil properties across soil depths, weather factors in different ecosystems and experimental variables. Methods We conducted a meta-analysis of 1231 experimental comparisons from 41 publications to explore the responses of native SOC to stable or radioactive carbon isotope (glucose) addition in laboratory incubation experiments representing various ecosystems and soil depths on the global scale. Results Overall, glucose addition had 110% positive PE on native SOC. The PE was higher in deep soil (197%) and lowest in topsoil (99%). Deep soil contains significantly lower SOC, dissolved organic carbon and microbial biomass carbon and a higher soil carbon/nitrogen ratio than topsoil. The PE positively correlated with soil carbon/nitrogen ratio and glucose addition rate but negatively correlated with microbial biomass carbon, dissolved organic carbon, SOC and incubation duration. Furthermore, PE positively related to mean annual temperature and precipitation in cropland while negatively correlated with mean annual precipitation in grassland ecosystem. Conclusions Low soil nutrients and high carbon/nitrogen ratio is the reason for higher PE in deep soil than topsoil. Furthermore, the experimental variables and weather factors provide a framework for understanding the magnitude and direction of PE on native SOC induced by glucose addition and highlight the need for future integrated approaches of studies on PE.

Aim: The aim was to explore how conversions of primary or secondary forests to plantations or agricultural systems influence soil microbial communities and soil carbon (C) cycling. Location: Global. Time period: 1993–2017. Major taxa studied: Soil microbes. Methods: A meta-analysis was conducted to examine effects of forest degradation on soil properties and microbial attributes related to microbial biomass, activity, community composition and diversity based on 408 cases from 119 studies in the world. Results: Forest degradation decreased the ratios of K-strategists to r-strategists (i.e., ratios of fungi to bacteria, Acidobacteria to Proteobacteria, Actinobacteria to Bacteroidetes and Acidobacteria + Actinobacteria to Proteobacteria + Bacteroidetes). The response ratios (RRs) of the K-strategist to r-strategist ratios to forest degradation decreased and increased with increased RRs of soil pH and soil C to nitrogen ratio (C:N), respectively. Forest degradation increased the bacterial alpha-diversity indexes, of which the RRs increased and decreased as the RRs of soil pH and soil C:N increased, respectively. The overall RRs across all the forest degradation types ranked as microbial C (−40.4%) > soil C (−33.3%) > microbial respiration (−18.9%) > microbial C to soil C ratio (qMBC; −15.9%), leading to the RRs of microbial respiration rate per unit microbial C (qCO2) and soil C decomposition rate (respiration rate per unit soil C), on average, increasing by +43.2 and +25.0%, respectively. Variances of the RRs of qMBC and qCO2 were significantly explained by the soil C, soil C:N and mean annual precipitation. Main conclusions: Forest degradation consistently shifted soil microbial community compositions from K-strategist dominated to r-strategist dominated, altered soil properties and stimulated microbial activity and soil C decomposition. These results are important for modelling the soil C cycling under projected global land-use changes and provide supportive evidence for applying the macroecology theory on ecosystem succession and disturbance in soil microbial ecology.

Soil moisture remarkably influences soil organic carbon (SOC) decomposition and is one of the key variables in ecological models influencing changes in soil carbon (C) storage. However, the mechanisms determining the impact of soil moisture on SOC decomposition in coastal wetlands are poorly understood. We collected and incubated soil samples from a coastal wetland of the Yellow River Delta, China, to investigate the response of SOC decomposition (the sum of CO2–C and CH4–C) to soil moisture. Soil samples were incubated at 20%, 60%, 100%, 140% and 180% water holding capacity (WHC), respectively. Compared to drought condition (20% WHC), moist (60% and 100% WHC) and flooding (140% and 180% WHC) conditions were observed with significantly higher SOC decomposition, explained by increased soil microbial biomass and altered soil physical parameters (pH and electronic conductivity (EC)). Excluding the effect of drought, we found decreased SOC decomposition with increased microbial biomass in flooding conditions compared to moist conditions. Structural equation modeling analysis showed that SOC decomposition and soil C storage were associated with changes in soil environment and soil microbial biomass resulted from soil moisture variation. This study highlights the importance of soil moisture in soil carbon dynamics, which is enlightening for the evaluation of soil C cycling with a decline of soil moisture under a warmer climate in coastal wetlands.

Two acidic soils (initial pH, 4.6) with contrasting soil organic C (SOC) contents (11.5 and 40 g C kg −1 ) were incubated with 13 C-labelled lime (Ca 13 CO 3 ) at four different rates (nil, target pH 5, 5.8 and 6.5) and three application depths (0–10, 20–30 and 0–30 cm). We hypothesised that liming would stimulate SOC mineralisation by removing pH constraints on soil microbes and that the increase in mineralisation in limed soil would be greatest in the high-C soil and lowest when the lime was applied in the subsoil. While greater SOC mineralisation was observed during the first 3 days, likely due to lime-induced increases in SOC solubility, this effect was transient. In contrast, SOC mineralisation was lower in limed than in non-limed soils over the 87-day study, although only significant in the Tenosol (70 μg C g −1 soil, 9.15%). We propose that the decrease in SOC mineralisation following liming in the low-C soil was due to increased microbial C-use efficiency, as soil microbial communities used less energy maintaining intracellular pH or community composition changed. A greater reduction in SOC mineralisation in the Tenosol for low rates of lime (0.3 and 0.5 g column −1 ) or when the high lime rate (0.8 g column −1 ) was mixed through the entire soil column without changes in microbial biomass C (MBC) could indicate a more pronounced stabilising effect of Ca 2+ in the Tenosol than the Chromosol with higher clay content and pH buffer capacity. Our study suggests that liming to ameliorate soil acidity constraints on crop productivity may also help to reduce soil C mineralisation in some soils.

Global warming modulates soil respiration (RS) via microbial decomposition, which is seasonally dependent. Yet, the magnitude and direction of this modulation remain unclear, partly owing to the lack of knowledge on how microorganisms respond to seasonal changes. Here, we investigated the temporal dynamics of soil microbial communities over 12 consecutive months under experimental warming in a tallgrass prairie ecosystem. The interplay between warming and time altered (P < 0.05) the taxonomic and functional compositions of microbial communities. During the cool months (January to February and October to December), warming induced a soil microbiome with a higher genomic potential for carbon decomposition, community-level ribosomal RNA operon (rrn) copy numbers, and microbial metabolic quotients, suggesting that warming stimulated fast-growing microorganisms that enhanced carbon decomposition. Modeling analyses further showed that warming reduced the temperature sensitivity of microbial carbon use efficiency (CUE) by 28.7% when monthly average temperature was low, resulting in lower microbial CUE and higher heterotrophic respiration (Rh) potentials. Structural equation modeling showed that warming modulated both Rh and RS directly by altering soil temperature and indirectly by influencing microbial community traits, soil moisture, nitrate content, soil pH, and gross primary productivity. The modulation of Rh by warming was more pronounced in cooler months compared to warmer ones. Together, our findings reveal distinct warming-induced effects on microbial functional traits in cool months, challenging the norm of soil sampling only in the peak growing season, and advancing our mechanistic understanding of the seasonal pattern of RS and Rh sensitivity to warming.

This work was financially supported by National Key Research and Development Program of China (2023YFE012400, 2020YFA0608100), Key Research Program of Frontier Sciences (ZDBS-LY-DQC019), National Natural Science Foundation of China (32371845, 42322306), Major Program of Institute of Applied Ecology, Chinese Academy of Sciences (IAEMP202201), International Partnership Program of Chinese Academy of Sciences (Grant No. 064GJHZ2022054FN) and the Youth Innovation Promotion Association CAS to Chao Wang (Y2022064). SM has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programmer (no. 101001608). FTM is supported by Generalitat Valenciana (CIDEGENT/2018/041) and the Spanish Ministry of Science and Innovation (PID2020-116578RB-I00 and EUR2022-134048). FTM and MD are supported by the Marc R. Benioff Revocable Trust and in collaboration with the World Economic Forum via the contract between ETH Zurich and University of Alicante ‘Mapping terrestrial ecosystem structure at the global scale’.