Strong links between aggregate stability, soil carbon stocks and microbial community composition across management practices in a Chinese dryland cropping system

Abstract

Increasing soil carbon (C) stocks and improving soil structure are critical challenges in semi-arid agroecosystems. Conservation tillage has been widely applied to promote aggregate stability, enhance soil organic C (SOC) storage, and conjointly influence microbial community composition. However, the relation among soil microbial groups, aggregate stability and SOC stocks under management practices remains unclear. We conducted a 17-year field experiment in a spring maize cropping system on the Loess Plateau of northwest China, comparing three types of management: conventional tillage with residue removal (CT-RR), reduced tillage with residue incorporation (RT-RI) and no-tillage with residue mulching (NT-RM). We evaluated aggregate stability index (ASI), SOC stocks and microbial community composition at 0–10 and 10–25 cm. The results showed that RT-RI and NT-RM significantly increased ASI by 11% and 16% relative to CT-RR in the 0–10 cm layer; RT-RI significantly increased ASI by 13% relative to CT-RR in the 10–25 cm layer (p < 0.05). The RT-RI increased the SOC concentrations and SOC stocks of macroaggregates (>250 μm), which harbor most of the total SOC stocks in bulk soil. Both RT-RI and NT-RM increased total microbial biomass and biomass of six microbial groups (i.e., gram-negative bacteria (GN), gram-positive bacteria (GP), total bacteria (B), total fungi (F), arbuscular mycorrhizal fungi (AMF) and saprophytic fungi (SF)) at 0–10 cm, and RT-RI increased the above groups at 10–25 cm. Across a range of microbial community indicators, we found strong positive relationships between SOC and GN, ASI and AMF in bulk soil. A random forest analysis indicated that GN and F were the best microbial predictors of SOC concentrations and overall aggregate stability, whereas AMF/SF was the best predictor of SOC concentrations within aggregates and the stability of individual aggregate size classes. These results demonstrated a strong link between aggregate stability, SOC dynamics and microbial community composition, and suggest that conservation tillage increases both soil aggregation and SOC storage, thus providing sustainability and technical feasibility for the development of dryland agroecosystems.