Simulated phytoremediation by root exudates of Sudan grass of soil organochlorine pesticides: impact on the rhizosphere microbial community.

ABSTRACT

The present work aims to study the efficiency of root exudates of Sudan grass on the degradation of organochlorine pesticides (OCPs) and the consequent impact on the microbial and ecological characteristics of the soil, including population composition, quantity dynamics, and community structure. Pot experiments were carried out to study the effect of root exudates on the degradation of OCPs at initial concentrations ranging from 66.67 to 343.61 mg/kg. In addition, the influence of root exudates on the rhizosphere microbial growth and their community structure was studied by monitoring the microbial biomass carbon, microbial biomass nitrogen, and phospholipid fatty acids (PLFAs) in the soils. In the range of OCP content (66.67 ~ 343.61 mg/kg), the soil-microbial system mediated by root exudates significantly promoted the removal of OCP pollutants. The removal rate of OCPs in the rhizosphere soil (TR2) was as high as 79.32%, 36.86% higher than that in the OCP-contaminated group (TR1) and 60.63% higher than that in the sterilized treatment group (CK). Under the same treatment conditions (pollution level and additive dose), the enhanced removal rate of HCHs, toxaphene, HCB, aldrin, and γ-chlordane by root exudates was much higher than the total amount of OCPs, while the extent of enhanced dissipation of DDTs, mirex, endosulfanI, dieldrin, and heptachlor epoxide was always lower than that in the corresponding soils. During the experiment, the phospholipid fatty acid content of bacteria was dominant, followed by that of fungi, and their variation trend was consistent with the degradation characteristics of OCPs in soil. Root exudates of Sudan grass might change the rhizosphere bacterial and fungal community structure during the process of phytoremediation, leading to enhanced OCP degradation.