Ecological mechanisms and effectiveness of bioremediation in Alaska

Abstract

What drives microbial community structure and function is a fundamental question of microbial ecology. Soil microbial communities have wide ranging metabolic capabilities, which include performing oxidation-reduction reactions responsible for cycling of nutrients and organic compounds and biodegradation of pollutants. One major determinant of microbial function in soils is vegetation type. Considering plants are diverse in chemical composition, they impact the quantity and quality of carbon and nutrients available to microbes through root turnover, root leachates, as well as by altering pH and soil microclimate (moisture, temperature). Rhizosphere interactions, in the form of phytoremediation, can be capitalized upon to provide a potentially cost effective method for detoxifying contaminated soils using plants and associated soil microorganisms. The remote locations and cold climate of Alaska provide unique challenges associated with phytoremediation such as finding effective plant species that can achieve successful site clean-up despite the extreme environmental conditions that includes minimal site management. Here we investigate the potential mechanisms and related effectiveness of microbial communities and native boreal vegetation associated with contaminant degradation and biogeochemical cycling. We examined three different soil systems to understand how dominant vegetation type, historical treatment and contamination shape the microbial community structure and functional potential. First, we used stable isotope probing to understand how microbial communities act in concert to biotransform the recalcitrant contaminants, polychlorinated biphenyls. Second, we sought to understand if dominant vegetation type controls microbial community structure and function either through direct impacts of plant root exudates and detritus or indirectly through the influence of plants on soil chemistry, composition, and structure. Finally, we conducted a forensic investigation of a petroleum contaminated site with no active site management for 15 years to assess the long-term effects of phytoremediation on soil petroleum concentrations, microbial community and vegetation colonization. The results of these experiments provide novel insights into the mechanisms of contaminant removal in boreal forest soils and the role of plants in ecosystem resilience to contamination, and demonstrates that phytoremediation using native and local plants can be an effective means to treat petroleum contaminated soils.