Effects of tillage regime on soil aggregate-associated carbon, enzyme activity, and microbial community structure in a semiarid agroecosystem

Conservation tillage enhances soil aggregate function, —a key factor for promoting soil nutrient cycling and plant growth. However, there is a limited understanding of how tillage practices impact soil nutrients, enzymes and microbes distribution among different-sized aggregates, and their potential subsequent effects on other soil functions and processes. We conducted a long-term experiment involving maize (Zea mays L.) cultivation in a semiarid farming region in Northwest China. Four tillages were implemented: no-tillage, minimal tillage, fold-tillage, and sub-tillage. Soil aggregates were categorized based on size: <0.25 mm ('micro'), 0.25–2 mm ('small'), and > 2 mm ('macro'). We measured the nutrient contents, enzyme activity, enzymatic stoichiometry, and soil microbial community structure with each fraction, and assessed crop productivity. The no-tillage treatment increased soil C content, microbial biomass, and P and N availability within micro-aggregates and bulk soil. It also enhanced enzymatic activity related to C and P acquisition and the C: N enzymatic ratio but decreased the N: P enzymatic ratio in micro-aggregates. Notably, no-tillage promoted straw and root biomass and crop yield compared to conventional tillage. Microbial community structure differed under the different tillage regimes and among aggregate size fractions, particularly under conventional tillage, but the tillage system did not affect alpha diversity. Our results highlight that long-term conservation tillage positively influenced soil aggregates by increasing carbon content and enzyme activity, thereby, reshaping the soil microbial community composition within aggregate size fractions in semiarid agroecosystems.