Understanding variations in soil properties and microbial communities in bamboo plantation soils along a chromium pollution gradient.

With high biomass productivity and resistance to heavy metals (HM) stress, bamboo has strong potential for HM phytoremediation. However, few studies have been conducted under field conditions to explore changes in soil physicochemical and microbial properties of bamboo forests with HM-contaminated soils. This study established bamboo (Phyllostachys praecox) plantations in five Cr-contaminated sites with different pollution levels (low, L; low-moderate, LM; moderate, M; moderate-high, MH; and high, H). We determined soil chemical properties, total and available Cr content, as well as bacterial and fungal community structures from 0 to 20 cm depth along the pollution gradient, and evaluated their interactions. The results revealed a corresponding decrease in soil pH, alkali-hydrolysable N (AN), along with urease and sucrase activities, as Cr pollution increased. In contrast, total organic carbon (TOC) increased with increasing Cr pollution. Soil available P (AP) and acid phosphatase activity did not differ significantly. Different pollution level resulted in distinct bacterial and fungal communities, with Proteobacteria, Acidobacteria, Actinobacteria, Ascomycota, and Basidiomycota being the dominant phyla across the five bamboo soils. Both total Cr (TCr) and HCl-extractable Cr (ACr) negatively correlated with alpha indices (Chao1 and Shannon) for bacteria but not for fungi, indicating that the latter is more resistant to Cr pollution. Decrease in soil pH and increase in TCr and ACr from L to H were closely related to the shift of bacterial and fungal communities. These changes reduced soil N and C cycles. Our findings suggest that improving soil acidic conditions and N availability enhances carbon and nitrogen cycles via altering soil microbial structure and activities. This, in turn, can increase phytoremediation efficiency in the bamboo ecosystem.