Influence of Crabgrass Root Exudates on the Hydrocarbons Degrading Microorganisms in Crude Oil Contaminated Soil

Abstract

Understanding plant‒microbial interactions in petroleum-contaminated soil is critical for enhancing phytoremediation technology. In this study, the root exudate of crabgrass (Digitaria ciliaris) was collected hydroponically, and its dominant composition was identified via GC‒MS. A soil microcosm study was subsequently conducted to evaluate the influence of crabgrass root exudates on microbial growth, dehydrogenase activity, and biodegradation of total petroleum hydrocarbons by the petroleum-degrading bacteria Micrococcus luteus WN01 and Acinetobacter lwoffii A07. The amendment of crabgrass root exudates significantly promoted microbial degradation in both A. lwoffii A07 (47.98%) and M. luteus WN01 (62.78%), which were 8.47% and 15.78% greater than those in the nonamended treatments, respectively. The dehydrogenase activity and microbial population were highest in the presence of root exudates. The crabgrass root exudates were predominantly composed of organic acids, phenolic compounds, and fatty acids, namely, 2-ketoisovaleric acid, acetylmethylcarbinol, ribitol, cinnamic acid, palmitic acids, and stearic acids, respectively. These chemical compounds in crabgrass root exudates can stimulate microbial dehydrogenase activity and total petroleum hydrocarbon (TPH) degradation in crude oil-contaminated soil. Further studies on how these individual chemicals may promote the degradation activity of hydrocarbon-degrading bacteria could provide a better understanding of the phytostimulatory effect of crabgrass during the phytoremediation of petroleumcontaminated soil.