Little environmental adaptation and high stability of bacterial communities in rhizosphere rather than bulk soils in rice fields

Abstract

The rhizosphere harbors complex bacterial communities, which are critical for plant growth and health. Significant differences exist between bacterial communities in the rhizosphere and bulk soils, however, limited research has explored co-occurrence patterns, environmental adaptations, and assembly mechanisms of rhizosphere bacterial communities. Using 16S rRNA high-throughput sequencing, we investigated the taxonomic and phylogenetic diversity of bacterial communities in both rhizosphere and bulk soils from a rice cropping experimental system in China. In addition to investigating differences in bacterial composition, we examined co-occurrence patterns, estimated environmental breadth and phylogenetic signals, and analyzed community assembly processes in these environments. Significant differences were observed between rhizosphere composition and bulk soil (p < 0.05) even some bacteria in the rice rhizosphere may come from the bulk soil around roots. The distribution patterns and ecological functions between communities in the rice rhizosphere and bulk soil were also significantly different. Lower β-diversity values among bacterial communities in the rice rhizosphere indicated that they had a higher stability than those in the bulk soils. In addition, rice rhizosphere communities had a wider phylogenetic diversity and lower functional redundancy when compared with bulk soils. Moreover, the results of environmental breadth analysis revealed that communities in bulk soils were more environmentally constrained than rhizosphere communities. Our null model revealed that deterministic processes drove community assembly in bulk soils (59.57%), whereas stochastic processes determined those in the rice rhizosphere (53.85%). Available potassium was decisive in determining the balance between stochasticity and determinism in both communities. Our study provides insights on the mechanisms underlying the assembly and maintenance of bacterial diversity in rice cropping soils, in response to environmental changes.