Crop type drives soil bacterial community and functional structure on the Loess Plateau terraces of China

Although terraced fields play an important role in soil and water conservation and agricultural production, the effects of planting different crops on the terraced soil bacterial community and functional structure are still unclear. We compared bacterial communities and functional structures in terraced soils grown with different crops on the Loess Plateau using the MiSeq technique. Economic crop types (apple [Malus domestica], greenhouse, intercropping), traditional crop types (corn [Zea mays], potato [Solanum tuberosum]), and terraced fields abandoned for five years in two small catchment areas in Ansai, Shaanxi, were selected, and the composition of the bacterial communities and other physicochemical properties of the soil were analyzed. The numbers of operational taxonomic units and bacteria α-diversity in economic and traditional crop types were 1.05 to 1.23 times higher than those in abandoned land; the change in crop types had significant effects on the soil bacterial community, and soil available phosphorus (P) content and bulk density were the main factors affecting the soil bacterial community. The dominant phyla were Proteobacteria, Acidobacteria, Actinobacteria, and Gemmatimonadetes, and the Proteobacteria accounted for 35% of the community in greenhouses but 30% in abandoned land. The co-occurrence networks indicated that economic crop types increased the links between soil bacterial taxa and the intensity of stability for terraced agroecosystems, especially for copiotrophic groups (Proteobacteria). Economic crop types enhanced potential functions of nitrogen (N) fixation and the carbon (C) cycle and reduced soil pathogens. These observations indicate that scientific planting and management could improve soil quality and health, which is conducive to sustainable agricultural development on the Loess Plateau terraces.