Long-term phytoremediation using the symbiotic Pongamia pinnata reshaped soil micro-ecological environment

Understanding the effects of phytoremediation on ecological environments is a core issue in soil bioremediation. However, the response of soil micro-ecological environment to long-term phytoremediation of symbiotic legume is still unknown. To address this issue, we focused on the changes of soil physicochemical properties, microbial communities, ecological functions, and correlation relationships of microbial populations in the V[sbnd]Ti magnetite mine tailings subsoil and the natural topsoil after three years' in-situ phytoremediation using the symbiotic Pongamia pinnata. The results showed that the bioavailability of soil nutrients and metals had undergone different degrees of significant changes in the two different metallic soil types after phytoremediation. It was revealed by changes in alpha-diversity indices, relative microbial abundance, LEfSe scores, and the number of significant OTUs that long-term phytoremediation using P. pinnata significantly altered soil microbial communities. This shift further caused a significant change in soil ecological functions and microbial community correlations. All changes in ecological functions caused by P. pinnata were in different degrees in the two different soil types. The Bray-Curtis based redundancy analysis (bcRDA) indicated that the shift of microbial communities was driven by several bioavailable nutrients and metals. Therefore, this study proved that long-term phytoremediation of symbiotic legumes could reshape soil microbial communities, and implied that a dramatic change in soil micro-ecological environment and an improvement of soil quality were the results of following long-term phytoremediation using the symbiotic legume.