Mild salinization stimulated glyphosate degradation and microbial activities in a riparian soil from Chongming Island, China

An incubation experiment was conducted to investigate the effects of simulated saltwater treatment with different percentages of artificial seawater on degradation dynamics of herbicide glyphosate and microbial activities in a riparian soil in Chongming Island, China. The results showed that 10% seawater treatment showed significantly enhancing effects on degradation efficiency of glyphosate with the lowest residual concentration among all the treatments. However, glyphosate degradation was markedly decreased in the riparian soil with 20% and 50% seawater treatments. The half-lives for 20% and 50% seawater treatments were prolonged by 12.1 and 39.0%, respectively, as compared to control. Microbial investigation indicated that 10% seawater treatment significantly stimulated microbial activities in the glyphosate-spiked riparian soil throughout the incubation period. At 42 day of incubation experiment, flourescein diacetate (FDA) hydrolysis rate, microbial adenosine triphosphate (ATP), and basal soil respiration (BSR) in the glyphosate-spiked riparian soil with 10% seawater were 59.2, 42.5 and 31.8% higher than those with no saltwater treatment, respectively. In contrast, saltwater treatment with 50% seawater significantly inhibited microbial activities. Especially, FDA hydrolysis rate, microbial ATP and BSR were decreased by 66.4, 58.6 and 66.8%, respectively, as compared to control. The results indicate that levels of simulated saltwater can exert variable effects on herbicide degradation dynamics and microbial parameters in the riparian soil.