Large-scale homogenization of soil bacterial communities in response to agricultural practices in paddy fields, China

Abstract

The transformation of natural habitats into cropland is a major issue in ecological conservation. Of particular concern is the large-scale biotic homogenization (reduced β-diversity) of soil microbial communities. Paddy fields represent the largest anthropogenic ecosystem in the world; however, bacterial homogenization and reduced biodiversity in paddy fields caused by intensive modern agricultural practices have yet to be explored. Here, samples were collected from 257 sites in four typical rice-growing regions across a 4,000-km transect in China, including both paddy fields and adjacent natural habitats. These four regions follow a unique gradient of rice cultivation management, from modern mechanical to traditional manual practices. Distance–decay patterns of bacterial communities in paddy fields revealed reduced β-diversity compared to surrounding natural habitats. Modern rice farming practices (plowing with machines) caused stronger homogenization of soil bacterial communities than traditional farming (plowing by hand). Among the four paddy regions, plowing by hand retained the highest soil bacterial β-diversity. Moreover, a significant inverse correlation was observed between bacterial β-diversity and the agricultural mechanization level. Among multiple environmental factors, dramatic spatial homogenization of soil physicochemical properties, particularly soil nutrient contents, and reduced dispersal limitation caused by modern farming activities both strongly predict a reduction of bacterial β-diversity in modern paddy fields.