No-tillage with green manure mulching enhances soil organic carbon stocks by strengthening macroaggregate-associated carbon and stimulating the cbbM functional gene in an arid oasis landscape

In arid agricultural landscapes, inappropriate tillage exacerbates the risk of soil organic carbon (SOC) loss and landscape degradation. Green manure (GM) incorporation is a beneficial practice, but the mechanisms by which different incorporation methods enhance soil organic carbon stocks (SOCS) by coordinating soil physical structure formation and microbial function remain unclear. This study aims to reveal the synergistic mechanism through which different incorporation methods enhances SOCS by coupling the physical protection of aggregates with microbial carbon fixation function. A three-year field experiment study was conducted in northwestern China's arid oasis agricultural zone, evaluating five management practices: (i) conventional tillage practices without GM cultivation during the fallow period (CT), (ii) no-tillage with GM mulching (NTG), (iii) no-tillage practice with aboveground biomass removal (NT), (iv) full incorporation of GM through tillage (TG), and (v) partial GM removal with only root residues incorporated via tillage (T). All GM incorporation practices significantly increased SOCS, with NTG showing the most pronounced effect. NTG promotes the >5 mm aggregates proportion, aggregate stability, and aggregate SOC content. Notably, >5 mm aggregates SOC content is significantly higher than in other particle sizes, and these aggregates contribute the most to SOCS. From a molecular perspective, SOCS is significantly positively correlated with the cbbM gene. NTG reduces the diversity of the carbon sequestration key functional gene cbbM but increases its abundance. Therefore, NTG synergistically enhanced soil carbon sequestration by promoting the formation and physical protection of macroaggregates and specifically enriching microbial functional genes with carbon fixation potential in the arid oasis agricultural landscape.在干旱农业景观中，不合理耕作会加剧土壤有机碳（soil organic carbon, SOC）流失与景观退化的风险。绿肥（green manure, GM）还田是一项有益的耕作措施，但不同还田方式通过协调土壤物理结构形成与微生物功能，提升土壤有机碳储量（soil organic carbon stocks, SOCS）的具体机制仍不明确。本研究旨在阐明不同还田方式通过耦合团聚体物理保护与微生物固碳功能，提升SOCS的协同作用机制。研究于中国西北干旱绿洲农业区开展了为期三年的田间定位试验，设置了5种耕作管理措施：(i) 休耕期不种植绿肥的常规耕作（conventional tillage, CT）；(ii) 免耕配合绿肥覆盖（no-tillage with GM mulching, NTG）；(iii) 免耕并移除地上生物量（no-tillage with aboveground biomass removal, NT）；(iv) 全量翻压绿肥（full incorporation of GM through tillage, TG）；(v) 仅翻压根茬并移除部分绿肥（partial GM removal with only root residues incorporated via tillage, T）。所有绿肥还田措施均显著提升了SOCS，其中NTG的调控效果最为显著。NTG可提升>5 mm粒径团聚体占比、团聚体稳定性及团聚体有机碳含量。值得注意的是，>5 mm粒径团聚体的有机碳含量显著高于其他粒径分级，且此类团聚体对SOCS的贡献度最高。从分子生物学视角来看，SOCS与固碳关键功能基因cbbM（cbbM gene）呈显著正相关。NTG会降低cbbM基因的群落多样性，但提升其丰度。因此，在干旱绿洲农业景观中，NTG通过促进大团聚体的形成与物理保护作用，同时富集具备固碳潜力的微生物功能基因，协同提升了土壤固碳能力。