Stochastic processes drive bacterial and fungal community assembly in sustainable intensive agricultural soils of Shanghai, China

Sustainable intensive cropping systems have been implemented for three decades in suburban agricultural dis-tricts of Shanghai, China. These human-managed soils have been developed from paleosol or alluvial soils across different regions. However, little is known about the geographical distribution patterns of microbes and microbial community assembly in the sustainable intensive soils after decades of anthropogenic disturbances. Here, we in-vestigated the impact of local geochemical properties and geographic distance on stochastic/deterministic micro-bial community assembly processes using high-throughput sequencing and phylogenetic null modeling analysis. Our results showed that soil pH was the most important environmental factor determining bacterial and fungal community structure. Importantly, only soil organic matter was positively correlated with fungal alpha-diversity, suggesting the efficient use of carbon substrates in sustainable agricultural systems, compensating for the lack of chemical fertilization and reduced tillage in these systems. Both bacterial and fungal communities had robust distance-decay patterns, but the rate of turnover of bacterial taxa was faster than that of fungi. Variation in bac-terial and fungal communities was mostly attributed to the simultaneous effects of environmental variables and spatial factors. We also mapped the spatial distributions of the dominant bacterial and fungal taxa across the sus-tainable agricultural fields, making it possible to forecast the responses of agricultural ecosystems to anthropo-genic disturbance. Based on the patterns of the beta-nearest taxon index, this study demonstrated that stochastic processes shaped substantial bacterial and fungal community variation in sustainable intensive agricultural soils of the Shanghai suburbs. This variation may be attributed to the increasing microbial dispersal caused by hy-drological connectivity in the agricultural fields or the release from environmental stress and weakened environ-mental filtering across the suitable pH range preferable for most soil microbes. These results unveil assembly mechanisms of soil microbial community after several decades of sustainable intensive management, and contribute to understand the role of microbes in ecosystems in establishing a functional equilibrium which may enable sustainability to be preserved. (C) 2021 Elsevier B.V. All rights reserved.