Bensulfuron‐methyl Biodegradation and Microbial Parameters in a Riparian Soil as Affected by Simulated Saltwater Incursion

Abstract

AbstractSoil salinization due to saltwater incursion, is a major threat to microbial population and thus strongly alters biogeochemical processes in a freshwater riparian of coastal estuary region. An incubation experiment was conducted to investigate the effects of simulated saltwater treatments with different percentages of artificial seawater on biodegradation dynamics of herbicide bensulfuron‐methyl (BSM) and microbial ecophysiological parameters in a riparian soil in Chongming Island, China. The results showed that saltwater addition with 10% seawater significantly increased the biodegradation efficiency of BSM with the lowest residual concentration among all the treatments. However, BSM degradation was markedly decreased in the riparian soil with high levels of saltwater treatment. The half‐lives for 20% and 50% seawater treatments were prolonged by 4.9% and 21.1%, respectively, as compared to no saltwater treatment. Throughout the incubation period, 10% seawater treatment showed significantly stimulating effects on microbial parameters in the BSM‐spiked riparian soil. At the end of incubation experiment, flourescein diacetate (FDA) hydrolysis rate, soil microbial adenosine triphosphate (ATP), and basal soil respiration (BSR) in the BSM‐spiked riparian soil with 10% seawater were 64.2%, 48.9%, and 39.4% higher than those with no saltwater treatment, respectively. In contrast, saltwater treatment with 50% seawater significantly inhibited microbial activities, relative to no saltwater treatment. Especially, FDA hydrolysis rate, microbial ATP, and BSR were decreased by 74.1%, 69.8%, and 63.4%, respectively, as compared to no saltwater treatment. Our data indicate that different levels of simulated saltwater incursion can exert variable effects on microbial ecophysiological parameters, and consequently resulted in the difference in biodegradation dynamics of herbicide in the herbicide‐spiked riparian soil.