Responses of Bacterial Community in Cotton Rhizosphere Soil to the Application of Chitosan under Different Cultivation Patterns

Abstract Aims Continuous cropping leads to the decreasing of soil nutrients and microbial diversity. This study aims to explore the effects of chitosan application on soil nutrient, enzyme activity, root exudates, and bacterial diversity in cotton field.Methods Topsoils were collected from four treatments (continuous cotton cropping (Ct), continuous cotton cropping with chitosan application (CtC), rotation (Rt) (cotton-corn-wheat), and rotation with chitosan application (RtC)) to determine the effects of chitosan on soil nutrients, enzyme activity, root exudates, and bacterial diversity under different cultivation patterns. The structure and functions of bacterial communities were analyzed using Illumina MiSeq sequencing and PICRUSt approach.Results Root exudates in CtC, Rt, and RtC treatments were higher than that in Ct treatment, while soil nutrients were lower. Soil enzyme activities were higher in Rt treatment than in Ct treatment, while only catalase activity was higher in CtC treatment. The abundance of Actinomycetes, Proteobacteria, Chloroflexi, and Bacteroidetes in Rt and CtC treatments, Firmicutes in Rt treatment, and Gemmatimonadetes in CtC treatment were higher than those in Ct treatment. PICRUSt analysis showed that the abundance of functional genes for soil microbial metabolism, environmental information processing, and organismal systems were higher in Rt, CtC, and RtC treatments than in Ct treatment, while that of genes for genetic information processing, cellular processes, and human diseases were slightly higher. Conclusions Chitosan application in cotton fields under different cultivation patterns could improve nutrient availability in continuous-cropping soils by reducing root exudates and improving soil bacterial community diversity, to reduce continuous cropping obstacles.