Conservation tillage regulates aggregate organic carbon and microbial communities in aeolian sandy soil

Aeolian sandy farmland in arid and semi-arid regions is often constrained by loose texture, weak aggregate stability, and low soil organic carbon (SOC), which limit soil quality improvement under intensive cultivation. Identifying management practices that improve aggregation and carbon retention while altering soil microbial communities is important for sustainable production in these systems. A three-year field experiment was carried out on aeolian sandy farmland in Hotan, Xinjiang, China. Four tillage management treatments were set up, including conventional tillage (CT), sole no-tillage (NT), no-tillage with sheep manure organic fertilization (NTOF), and no-tillage with straw mulching (NTSM). The NT and NTSM treatments showed greater mega-aggregate formation and higher mean weight diameter (MWD) than CT, and NTSM gave the most evident increase in aggregate-associated organic carbon, particularly in the mega-aggregate fraction. The implementation of all three conservation tillage practices had no significant effect on microbial alpha diversity; however, NT, NTOF and NTSM significantly influenced bacterial community composition, whilst NTSM significantly altered fungal community composition and caused the bacterial network to shift from being predominantly characterized by negative correlations to positive correlations. Relationships between mega-aggregate microbial community characteristics and SOC or mean weight diameter (MWD) were treatment dependent. Structural equation modelling suggested potential linkage pathways among soil properties, microbial community structure, SOC accumulation, and aggregate stability. Overall, NTSM showed the strongest overall response, as reflected by improved soil conditions, greater aggregate-associated carbon accumulation, enhanced aggregate stability, and distinct changes in mega-aggregate microbial communities. These findings suggest that no-tillage with straw mulching may be a promising management option for improving soil structure and carbon retention in aeolian sandy farmland.