Artificial root exudates restore microbial functioning in a metal contaminated, barren, inactive soil

Restoring enzyme function in barren, brownfield soils using green strategies can improve microbial functioning and enable phytoremediation. It is known that adding simple, readily metabolized substrates secreted by growing plant roots (root exudates) or a laboratory prepared solution of root exudates (artificial root exudates) can stimulate soil microbial function. It is not known whether and how well this strategy works in a contaminated, low functioning soil from an industrial barren site because contaminants in the barren soil might inhibit microbial survival and functioning, or the microbial community might not be adapted to functionally benefit from root exudates. The objective of this study was to determine whether artificial root exudates stimulate microbial function in a barren soil. We collected soils from a barren brownfield (25R) site and an adjacent vegetated brownfield site (25F), with low and high enzyme activities, respectively. We subjected both soils to three treatments: switchgrass (native to the site), artificial root exudates, and a combination of switchgrass and artificial root exudates. We measured enzymatic activity, plant growth, soil moisture, organic matter content, and easily extractable glomalin content over 205 days. By day 157, artificial root exudates increased the phosphatase activity by 9-fold in previously vegetated brownfield soil and by 351-fold in barren brownfield soil. When exudates were added to the barren soil, the plant shoot mass was higher (52.2 ± 2.5 mg) than when they were not (35.4 ± 3.6 mg). In both soils, adding artificial root exudates significantly increased the percent moisture, organic matter, and glomalin content. Treating contaminated, barren soil with artificial root exudates resulted in increased soil microbial function and improved soil properties that might promote a hospitable habitat to support vegetation in such extreme environments. Summary: We added artificial root exudates to stimulate enzymatic function in two contaminated soils. Plant shoot mass, soil percent moisture, glomalin content, and organic matter content significantly increased due to the addition of artificial root exudates to the study soils. Microbially-mediated phosphatase activity was established in a barren, previously inactive, polluted soil.