Soil carbon increase with straw returning: New evidence from soil extracellular enzymes

Straw returning is an effective practice to sequester soil carbon in agricultural soils. However, the response of soil extracellular enzyme activities (EEAs) to straw returning and their linkages to soil carbon pools remain poorly understood. Here, we present a global meta-analysis on the effect of straw returning on soil hydrolytic carbon-acquiring (<em>C-acq</em>) EEAs and their relationships with soil carbon pools in agricultural ecosystems. On average, straw returning increased <em>C-acq</em> EEAs by 23.2%, soil microbial biomass carbon (MBC) content by 29.2%, and soil organic carbon (SOC) storage by 21.1%, relative to no straw returning. The effect of straw returning on MBC content and SOC storage is best explained by their positive relationships with <em>C-acq</em> EEAs: when straw returning strongly stimulates <em>C-acq</em> EEAs, MBC content and SOC storage increase; conversely, when straw returning weakly stimulates <em>C-acq</em> EEAs, MBC content and SOC storage decline. Furthermore, soil pH and straw amount best predicted the straw returning effects on <em>C-acq</em> EEAs. Our results provide the first evidence that <em>C-acq</em> EEAs are linked to soil carbon increases under straw returning in agricultural ecosystems. Incorporating the soil microbial effects of straw returning revealed here on agricultural soils into Earth system models could improve predictions of soil carbon dynamics.

秸秆还田是农业土壤固碳的有效实践手段。然而，土壤胞外酶活性（soil extracellular enzyme activities, EEAs）对秸秆还田的响应及其与土壤碳库的关联机制仍有待深入阐明。本研究开展了一项全球元分析，探讨秸秆还田对农业生态系统中水解性碳获取型胞外酶活性（C-acq）的影响，及其与土壤碳库的相关关系。结果显示，相较于不秸秆还田处理，秸秆还田平均可使C-acq酶活性提升23.2%，土壤微生物量碳（MBC）含量提升29.2%，土壤有机碳（SOC）储量提升21.1%。秸秆还田对MBC含量与SOC储量的调控效应，可通过二者与C-acq酶活性的正向关联得到最佳解释：当秸秆还田强烈激发C-acq酶活性时，MBC含量与SOC储量均会上升；反之，当秸秆还田对C-acq酶活性的激发作用较弱时，MBC含量与SOC储量则会下降。此外，土壤pH与秸秆还田用量可最佳预测秸秆还田对C-acq酶活性的调控效应。本研究首次证实，农业生态系统中秸秆还田场景下，C-acq酶活性与土壤碳储量提升存在显著关联。将本研究揭示的秸秆还田对农业土壤的微生物调控效应纳入地球系统模型，可提升对土壤碳动态的预测准确性。