Soil Microbial Communities and Metabolic Function of a Northern Alabama Forest Ecosystem.

Thinning, prescribed burning, and their combinations, are common forest management practices to restore degraded forest communities and to prevent uncontrollable wildfires. However, their impacts on soil microbial communities, which are vital to global element cycling, are traditionally overlooked. In this study, the effects of thinning and burning on microbial communities and metabolic functions was evaluated in a forest ecosystem using ester-linked fatty acid methyl ester (EL-FAME) coupled with assays of enzymes important in carbon, nitrogen, phosphorus, and sulfur cycling, such as laccase, manganese peroxidase (MnP), xylanase, β-glucosidase, β-glucosaminidase, acid phosphatase, and arylsulfatase. The treatments comprised of three burning patterns (no burn, 3yr- and 9yr- burn cycles) and three levels of thinning (no thin, lightly thinned, and heavily thinned) in a completely randomized design layout located at the Bankhead National Forest of Alabama. Five years after treatments were initiated, microbial communities increased in the lightly-thinned plots and decreased in the burn-only plots compared to the no-burn/no-thinned (reference) plot. Thinning promoted soil ligninolytic enzymatic activities, as both lightly- and heavily-thinned treatments exhibited greater laccase and MnP activities than the no-thinned plots. There was increase in hydrolysis of hemicellulose with thinning, as demonstrated by xylanase activities. Lower activities of β-glucosidase in the heavily-thinned treatments correspond to an increase in the deposition of woody material with restricted access to cellulose. Geometric mean enzyme activity (GMea) index of all seven enzymes were greater under the lightly thinned plots than the heavily-thinned and no-thinned plots, with implications of potential higher metabolic function under those practices. Overall, the light thinning increased the relative abundance of the microbial communities, and the metabolic capacity of the soil.