Evaluation of Microbial Diversity, Community Composition and Function in Mixed Cropping Systems Using Three Legume Species Under the Application of Biochar or Chemical Fertiliser

Abstract

Mixed cropping systems involve utilising multiple crop species on the field and diversifying aboveground plants. However, several contradicting results have been reported regarding their effects on soil microbial diversity. Therefore, to evaluate the effects of different leguminous species used in mixed cropping systems and the types of fertiliser on the diversity of soil microbes, a pot study was performed under maize/legume mixed cropping systems with one of three legumes, including cowpea [Vigna unguiculata (L.) Walp.], velvet bean [Mucuna pruriens (L.) DC.] and common bean (Phaseolus vulgaris L.) , and one of three types of fertiliser treatments, namely chemical fertiliser (CF), carbonised chicken manure (CM) or the lack of fertiliser (Ctr). 16S rRNA analyses were conducted using the soils sampled from each pot for soil bacterial diversity assessment, and Tax4Fun2 was used for bacterial functional prediction analysis. A decrease in microbial diversity after CM application was observed in the soil with velvet bean + maize (MM) compared to the Ctr treatment, whereas an increase in microbial diversity was observed in the soil with common bean + maize (PM) in the same condition. With CM application, the abundance of treatment-unique bacteria increased with PM treatment, whereas their decrease was observed with MM treatment. In contrast, the abundance of dominant microbes, including Thaumarchaeota, Chloroflexi, Planctomycetes and Verrucomicrobia, was significantly lower in PM but higher in MM after CM application. Functional prediction analysis indicated that the dominant bacteria were involved in CM decomposition processes and nitrification in MM treatment. Legume species-dependent factors, including nutrient absorption and root exudate composition, might be important concerning soil bacterial diversities.