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.