Evaluation of microbial diversification mechanisms in legume-based mixed cropping systems with different legume species and types of fertilizer management

Biodiversity loss is becoming a global concern due to its negative impact on services associated with the ecosystem. For agricultural soil to maintain these multi-services, the conservation of soil microbial diversity is of utmost importance. Mixed cropping systems involve the utilisation of multiple crop species on the field as well as the diversification of aboveground plants, although several contradicting results have been reported regarding their impacts on soil microbial diversity. Therefore, for the evaluation of the impact of different leguminous species used in mixed cropping systems as well as types of fertilizer 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 unguiculate (L.) Walp.), velvet bean (Mucuna pruriens (L.) DC.), and common bean (Phaseolus vulgaris L.) as well as one of three types of fertilizer treatments, namely chemical fertilizer (CF), carbonised chicken manure (CM), or the lack of fertilizer (Ctr). 16S rRNA analyses were conducted using the soils sampled from each pot for soil bacterial diversity assessment. Concerning the results, a decrease in the microbial diversity after CM application was shown by the soil with velvet bean + maize (MM) when compared to the Ctr treatment, while an increase in the microbial diversity was shown by the soil with common bean + maize (PM) under the same condition. In case of the CM application, the abundance of treatment-unique bacteria increased in the PM treatment, although their decrease was observed for the MM treatment. In contrast, the abundance of dominant microbes, including Thaumarchaeota was significantly lower in PM but higher in MM when the CM was applied. Legume species-dependent factors, including nutrient absorption and root exudate composition might be important concerning soil bacterial diversities. For the conservation of soil microbial diversity with mixed cropping, the interaction effect of legume species and fertilizer type should be considered in future studies.