Microbial community composition and enzymes of a forest ecosystem in Alabama: Initial response to thinning and burning management selections

Authors: NTOKO, FRITZ - Alabama A & M University; GARDNER, TERRENCE - North Carolina State University; SENWO, ZACHARY - Alabama A & M University; Acosta-Martinez, Veronica

Submitted to: Journal of Forestry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2018
Publication Date: 7/18/2018
Citation: Ntoko, F., Gardner, T., Senwo, Z., Acosta Martinez, V. 2018. Microbial community composition and enzymes of a forest ecosystem in Alabama: Initial response to thinning and burning management selections. Journal of Forestry. Journal of Forestry, 2018, 8, 328-343.

Interpretive Summary: Prescribed burning and tree thinning are common restoration practices for U.S. forests to increase forest productivity and enhance plant and animal diversity. The impact of these practices in Alabama’s Bankhead National Forest on the soil microbial component and overall forest soil health were investigated by scientists from USDA-ARS in Lubbock TX, Alabama A & M University and North Carolina State University. They found that heavily-thinned plots without burning or less frequent burning seemed to provide more favorable conditions for the microbial component (including increasing fungi) due to higher soil pH and lower C:N ratios. Prescribed burning reduced the microbial component probably due to depletion of labile C sources with the high temperatures, leaving mostly recalcitrant (complex) C sources as available soil energy sources. This study identified benefits in thinning rather than burning to the soil microbial community, which is important to sustain essential soil functions in a forest ecosystem.

Technical Abstract: Prescribed burning and tree thinning are commonly used restoration practices for US forests management to increase forest productivity and enhance plant and animal diversity. The impact of these practices in Alabama’s Bankhead National Forest (BNF) to soil microbial components and overall forest soil health are unknown. We hypothesized that microbial assemblages and enzyme activities are continuously changing in forest ecosystems especially due to management selections. Therefore, the objective of this study was to assess changes in microbial community compositions (fungal vs bacterial populations) via fatty acid methyl ester (FAME) profiling and several enzyme activities (ß-glucosaminidase, acid phosphatase, arylsulfatase, ß-glucosidase, xylanase, laccase, and manganese peroxidase) critical to soil organic matter (SOM) dynamics and biogeochemical cycling. In this forest, heavily-thinned plots without burning or less frequent burning treatments seemed to provide more favorable conditions (higher pH and lower C:N ratios) for C and N mineralization. This may explain a slight increase (by 12%) detected in fungi:bacteria (F:B) ratio in the heavily-thinned plots relative to the control. Thinned (lightly and heavily) plots showed greater ligninolytic (laccase and MnP) activities and lower ß-glucosidase and ß-glucosaminidase activities compared to the no-thinned plots probably due to increase depositions of woody recalcitrant C materials. We observed significant but negative correlations between the ligninolytic laccase and manganese peroxidase (Lac and MnP) enzymes respectively, with MBC (-0.45* and -0.68** respectively) and MBN (-0.43* and -0.65** respectively). Prescribed burning treatment reduced microbial biomass C and N of the 9-yr burned plot/lightly thinned plots probably due to depletion of labile C sources with the high temperatures, leaving mostly recalcitrant C sources as available soil substrates. Gram-positive bacteria (i15:0, a15:0, i17:0, and a17:0), actinomycetes (10Me17:0, 10Me18:0), AMF (16:1'5c), and saprophytic fungi (18:1'9c), largely contributed to the microbial compositions. This study bridges knowledge gaps in our understanding of microbial community compositions and enzyme-mediated processes in repeatedly burned and thinned forest ecosystems.