Crop diversity facilitates soil aggregation in relation to soil microbial community composition driven by intercropping

Studies verify that intercropping increases soil macro-aggregates but the mechanism underlying the increase is poorly understood. Three long-term field experiments were conducted starting in 2009 at three sites in an oasis in northwest China. The first was a split-plot design: Rhizobium (with or without inoculation) and three cropping systems (faba bean/maize intercropping and corresponding monocultures). The second and third experiments were both single-factorial randomized block designs with nine cropping systems (maize intercropped with faba bean, chickpea, soybean, or oilseed rape, and the corresponding monocultures). Soil aggregates were determined by the wet sieving method. Microbial biomass and community composition in 2015 and 2016 were determined by phospholipid fatty acid (PLFA) and high throughput sequencing analysis of 16S rRNA. Soil macro-aggregates (> 2 mm) in intercropping systems increased by 15.5–58.6% across three sites and two years, an effect derived partly from increased relative abundance of soil Sordariales, from enhanced arbuscular mycorrhizal fungi biomass, or from reduced relative abundance of Nitrospirae, depending on soil type. Intercropping alters soil microbial community composition and further facilitates soil aggregation. These findings provide insights into the mechanisms underlying the maintenance of biodiversity in ecosystem functioning.