华中农大Nature Geoscience：微生物胞外聚合物（EPS）是土壤稳定有机碳库的重要来源

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9月28日，国际地球科学期刊Nature Geoscience 在线发表华中农业大学资源与环境学院、农业微生物资源发掘与利用全国重点实验室蔡鹏教授团队在土壤生物地球化学领域的最新研究成果《微生物胞外产物是土壤矿物结合态有机碳库的重要来源》（“Microbial extracellular residues are a major source of mineral-associated soil carbon”）。本研究结合全国尺度农田土壤调查、稳定同位素示踪、生物标志物分析、固态¹³C核磁共振和纳米二次离子质谱等多尺度、多方法表征体系，系统揭示了土壤EPS的合成、转化与稳定是微生物向土壤输入稳定有机碳的重要途径，为理解微生物介导的土壤碳循环与稳定过程提供了新的视角。

针对这一关键科学问题，研究团队构建土壤EPS量化表征方法体系，结合全国农田土壤调查与稳定碳同位素标记实验，揭示出微生物胞外碳驱动土壤有机碳形成与稳定的新机制。该研究不仅拓宽了对SOC循环过程与机制的科学认知，也为精准评估土壤固碳潜力与应对气候变化提供了重要理论支撑。

由于缺乏量化标志物，EPS在复杂土壤有机质背景下难以实现准确的含量测定及动态通量评估。针对这一技术瓶颈，团队首先整合81组不同微生物来源EPS组分数据，发现EPS中的多糖和蛋白质碳占EPS总碳的比例稳定在74%左右，表明二者可作为定量表征土壤EPS碳的标志物。该方法可有效排除其他有机质的干扰，估算结果与实测值高度相关（R² = 0.89），同时具备良好一致性（IA = 0.96）。

在此基础上，团队进一步开发了基于酸沉淀、蛋白酶解和超滤筛分的EPS标志物纯化方案，并将其与相结合，通过定量分析¹⁸O在土壤胞外多糖和蛋白质中的掺入，准确测定了EPS的合成速率。该方法突破了土壤EPS含量及动态通量难以准确量化的技术限制，为深入解析微生物胞外碳的合成、转化过程及其生态功能提供了关键技术支撑。

图1 土壤EPS碳动态合成方法的建立

基于本研究建立的EPS定量方法，研究团队采集了覆盖中国南北约3624 km范围内的55个农田土壤样品，系统解析了土壤非矿物稳定态EPS碳含量及其产生速率。研究发现，尽管非稳态EPS碳仅占SOC总量的3.2%，但其产生速率与微生物细胞生物量的产生速率相近。这一结果首次表明，EPS是土壤微生物大量合成和释放的重要有机碳组分，并非传统认知中的“微量微生物产物

研究团队进一步基于全国尺度农田土壤样品，采用多元回归等统计分析发现，微生物来源有机碳与SOC均呈显著正相关。其中，EPS与土壤矿物结合态有机碳含量表现出较强的相关性，且这种关联不受微生物细胞碳含量的影响。梯度增强回归树和结构方程模型等分析进一步表明，微生物胞外产物是土壤矿物结合态有机碳的关键预测因子，而微生物细胞碳对于土壤矿物结合态有机碳变化解释能力相对较弱。这些结果表明，微生物胞外碳可能是土壤矿物结合态有机碳的重要来源。

图2 农田土壤EPS含量及其对矿物结合态有机碳的影响

为了进一步回答“EPS是否是土壤矿物结合态有机碳的重要来源”这一关键科学问题，研究团队制备了¹³C标记的微生物EPS，并分别将其与细胞残体和植物来源碳输入不同类型土壤中开展同位素示踪。结果显示，EPS输入显著提高了土壤矿物结合态有机碳含量。13C示踪分析表明，EPS来源碳能够有效形成土壤矿物结合态有机碳，且在部分土壤类型中的积累水平高于细胞残体，证明EPS是土壤矿物结合态有机碳的重要来源。

图3 稳定碳同位素示踪EPS有效进入土壤矿物结合态碳库

本研究结合全国尺度农田土壤调查、稳定同位素示踪、生物标志物分析、固态¹³C核磁共振和纳米二次离子质谱等多尺度、多方法表征体系，系统揭示了土壤EPS的合成、转化与稳定是微生物向土壤输入稳定有机碳的重要途径，为理解微生物介导的土壤碳循环与稳定过程提供了新的视角。理论框架，将微生物胞外碳输入与稳定路径纳入土壤碳循环研究体系。研究成果深化了对微生物源有机质形成、转化与稳定机制的认识，为解析全球变化背景下微生物组调控土壤碳归宿及其稳定性提供了新的理论依据，同时也为增强农田土壤碳汇能力、优化土壤碳管理措施提供了科学支撑。

图4 EPS介导的土壤碳固存途径

华中农业大学资源与环境学院博士研究生钱佩佩和

相关论文：

Qian, P., Wu, Y., Ren, J. et al. Microbial extracellular residues are a major source of mineral-associated soil carbon. Nat. Geosci. (2026). 

扩展阅读

Soil microbes play a crucial role in soil organic carbon storage by processing plant-derived carbon and producing microbial carbon, which can accumulate over time and form a substantial fraction of the soil organic carbon stock. Whereas the contribution of microbial cellular residues, the remains of dead microbial cells, to soil carbon storage is well established, the role of extracellular residues remains poorly quantified. Here we develop an 18O-H2O isotope-tracing method to quantify the production of extracellular polymeric substances, mucus-like mixtures of sugars, proteins and other biopolymers released by microbes and apply it across a national-scale survey of cropland soils in China. We find that extracellular polymeric substances constitute a major microbial carbon input to soils, with production rates comparable to those of microbial cellular residues and they exhibit statistical associations with mineral-associated organic carbon across soils. In 13C-labelling microcosm experiments, carbon derived from extracellular polymeric substances is incorporated into the mineral-associated organic carbon pool at rates comparable to or exceeding those of microbial cellular residues. These results identify the extracellular pathway as an important and previously underappreciated mechanism contributing to the mineral-associated carbon pool and provide mechanistic insights into how microbiomes shape the fate of soil carbon under global change.

Soils represent the largest active reservoir of carbon on our planet, contributing substantially to climate change mitigation1,2. Soil carbon dynamics and stocks are strongly governed by complex interactions among soil microbiomes, plant materials and minerals. Belowground communities transform plant-derived carbon into less degradable forms and produce microbially derived carbon, both of which can persist in soils for extended periods through close association with minerals3,4. Microbially derived carbon, including cellular and extracellular residues, constitutes a major fraction of soil organic carbon (SOC), particularly in cropland and grassland ecosystems5,6,7. Recent studies suggest that most microbially derived carbon comprises cellular residues8,9. But microbially exudated biopolymers, including polysaccharides, proteins and DNA, collectively referred to as extracellular polymeric substances (EPSs), are increasingly recognized as important contributors to the build-up of soil carbon stocks10,11,12,13. Previous research shows that the mass of EPSs often surpasses the biomass of their producers by several to dozens of times14,15,16. Yet we still lack a basic understanding of the relative contribution of cellular versus extracellular microbial residues to soil carbon stocks, which introduces considerable uncertainties in global carbon projections. Current uncertainty regarding the relative contribution of cellular versus extracellular microbial residues to soil carbon exists for three primary reasons. First, despite its ubiquity and abundance, accurately quantifying the carbon content of EPSs in soil remains a challenge. Current methods primarily focus on living and senesced biomass, such as phospholipid fatty acids and amino sugars biomarkers17,18, thereby underrepresenting the contribution of microbial extracellular products. Second, a combination of observational and experimental approaches aimed at quantifying the relative contribution of microbial cellular and extracellular products to soil carbon stocks is largely missing. Finally, the prevailing theory of microbially driven soil organic matter genesis posits that microorganisms transform plant inputs into partially decomposed plant residues and microbial products, which subsequently persist in soils through sorption on mineral surfaces or occlusion within soil aggregates19,20,21. Consequently, plant input quality and microbial physiological traits are expected to be important controls on the formation of mineral-associated organic carbon (MAOC)22. Yet recent studies suggest a partial decoupling between microbial cellular residue accumulation and MAOC accrual, suggesting that previously overlooked pathways beyond cellular residues contribute to SOC accumulation and preservation23,24,25. With strong sorption affinity towards mineral surfaces and strong soil aggregation capabilities26,27,28, EPSs may serve as an important source of MAOC. This hypothesis has rarely been empirically tested or quantified in a real soil environment, leading to a systematic underestimation of the microbial role in SOC sequestration22,29. Here we combine a national-scale survey with multiple microcosm studies to assess the contribution of EPSs to SOC stocks across croplands. We focus on croplands because these ecosystems could play a critical role as carbon sinks under the right land-management strategies, with the potential to counteract substantial SOC losses and address global warming and food security challenges30,31. We develop a quantitative approach to measure EPS carbon content and their production rate at the microbial–soil interface. We investigate the potential involvement of EPSs in SOC sequestration by examining their statistical associations with MAOC using multiple regression analyses, gradient boosting regression trees and path modelling. We further evaluate the importance of EPSs as a source to the MAOC pool using 13C isotopic labelling incubations, in which we compare the incorporation of EPSs, microbial cellular residue, glycerol and straw into MAOC.

来源：华中农业大学、Nature 官网

本月编辑：白露｜审核：EE编委团

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