Adaptability of agricultural soil microbial nutrient utilization regulates community assembly under mulching measures on the Loess Plateau

Soil microbial nutrients and resource availability improve with mulching in agroecosystems, resulting in changes of soil microbial nutrient utilization strategies. However, the responses of soil microorganisms to nutrient utilization processes to regulate community assembly and thus maintain resource availability have not been clarified. Here, we performed a long-term field experiment with mulching measures, including no-mulching (NM), straw mulching (SM), plastic mulching (PM), and ridge mulching (RM), conducted on the Loess Plateau of China, to explore the community assembly process in response to microbial nutrient utilization. Microbial nutrient utilization strategies were analysed by measuring soil nutrients, microbial biomass, and extracellular enzyme activities. The results showed that PM and RM acquired C and N nutrients by secreting C- and N-extracellular enzymes in response to C:N- and C:P imbalances in soil chemistry, thereby reducing the nutrient limitation on microbial metabolism and improving microbial C utilization efficiency (CUE). Soil extracellular enzymatic stoichiometry increased and N utilization efficiency (NUE) decreased under mulching and drove an increase in beta-diversity and dominant species abundance in fungal communities. Mulching measures promoted the modular distribution of sensitive microorganisms and aggregation of fungal networks under PM and RM by reducing the stoichiometric imbalance and extracellular enzymatic N:P. At the same time, the microbial community assembly gradually changed from a stochastic to a deterministic process in response to the alleviation of soil C:P imbalance and changes in microbial nutrient utilization, in which the fungal community was dominant. In conclusion, soil microorganisms adaptively responded to changes in soil microbial nutrient utilization through the enhancement of aggregation of fungal co-occurrence networks and deterministic assembly processes. This study provides a better understanding of the impact of mulching on microbial nutrient utilization strategies from a community assembly perspective.