Responses of abundant and rare subcommunities to bioremediation conducted by Pseudomonas chenduensis in cadmium contaminated paddy soil. pot experiment

Crops cultivation in the cadmium (Cd)-contaminated paddy soil causes great risk for food safety. In situ soil bioremediation conducted by functional microorganisms has been increasingly applied. However, how local microbiota responded to bioremediation processes accompanying with crop cultivation, and its effect on uptake of Cd by rice is rarely discussed. Here, Pseudomonas chenduensis strain MBR was applied to remedy Cd-contaminated paddy soil, during which microbial community dynamics were investigated. The results showed that bioremediation by strain MBR significantly lessened Cd accumulation in rice grains and root, and meanwhile caused great dynamics of microbial communities in rhizosphere soil but less dynamics in bulk soil. Although both abundant and rare subcommunities showed great variations during bioremediation, they exhibited distinct temporal trajectories. Mantel and partial mantel tests showed that microbial communities in paddy soil without bioremediation tended to be structured by stochastic processes, while bioremediation caused important roles of edaphic factors and cadmium pressure in regulating microbial communities, which worked only in rhizosphere soil. Consequently, effects of bioremediation by strain MBR on local communities depended on types of subcommunities (abundant and rare) and soils (rhizosphere and bulk). This study shed light on microecological processes during bioremediation accompanying with crop cultivation in situ.

镉（Cd）污染稻田土壤中的作物种植，会给食品安全带来极大风险。采用功能微生物开展的原位土壤生物修复技术应用日益广泛。然而，目前鲜有研究探讨本地微生物群落在伴随作物种植的生物修复过程中如何响应，以及其对水稻吸收镉的影响。本研究采用成都假单胞菌（Pseudomonas chenduensis）MBR菌株修复镉污染稻田土壤，并同步解析了其中的微生物群落动态变化。结果表明，MBR菌株的生物修复可显著降低水稻籽粒与根系的镉积累量，同时显著改变根际土壤的微生物群落动态，而对非根际土壤的微生物群落动态影响较小。尽管在生物修复过程中，丰富类群与稀有类群亚群落均发生了显著变化，但二者展现出截然不同的时间动态轨迹。曼特尔（Mantel）检验与偏曼特尔检验结果显示，未进行生物修复的稻田土壤微生物群落主要由随机过程主导；而生物修复则使得土壤理化因子与镉胁迫在调控微生物群落结构中发挥了关键作用，且该效应仅存在于根际土壤中。因此，MBR菌株生物修复对本地微生物群落的影响，取决于亚群落类型（丰富类群与稀有类群）以及土壤类型（根际与非根际）。本研究阐明了原位作物种植条件下，生物修复过程中的微生物生态机制。