Rhizosphere responses to environmental conditions in Radix pseudostellariae under continuous monoculture regimes

The root exudates of Radix pseudostellariae, working as a rhizospheric intermediary between plants and microbes, can deteriorate the microbial community in the rhizosphere in a consecutive monoculture system. We assessed the effects of artificially applied R. pseudostellariae root exudates on R. pseudostellariae seedling growth, rhizosphere soil microbial communities, and soil physicochemical properties. We found that phenolic acids and organic acids acted as a driver of changes in the microbial community. High-throughput sequencing and qRT-PCR analysis demonstrated that treatment with phenolic acids significantly decreased the relative abundance of Trichoderma, Penicillium, Pseudomonadales, Xanthomonadales, and Streptomycetales. Organic acids had a significant negative effect on the relative abundance of Pseudomonadales and Streptomycetales and significantly increased the abundance of Fusarium, Xanthomonadales, Micrococcales, and Gemmatimonadales. Analysis based on the noninvasive microtest technique indicated that root exudates increased H+ efflux and plasma membrane H+-ATPase activity in the pathogenic fungi and decreased them in the beneficial fungi. These phenomena created an acidic environment for the inhibition of beneficial bacteria and accumulation of specialized plant pathogens. This study explains the mechanisms underlying the shift in microflora and structural disorder caused by root exudates in continuously monocultured R. pseudostellariae rhizosphere soil through responses to environmental conditions.