Microbial mediated effects of thinning on methane oxidation rates in forest soils

Thinning has been widely used in forest management to improve the quality of timber products, to protect biodiversity and to maintain ecosystem functions. Thinning can influence aboveground and belowground forest characteristics such as community structure, intensity of illumination and soil abiotic factors, which, in turn, can affect soil microbial processes. Effects of thinning on vegetation and soil abiotic factors have been well documented but its effect on soil microbial process and greenhouse gas fluxes are still not well understood.

In this study, we explored the changes in soil properties, extracellular enzyme activities and greenhouse gas flux (CO₂, CH₄) in forests with different thinning intensities. Intensities of thinning were classified as control (CK, 800 trees / ha), low intensity thinning (LIT, 700 tree / ha), mid intensity thinning (MIT, 600 tree / ha) and high intensity thinning (HIT, 500 tree / ha). Soil CO₂ and CH₄ fluxes were measured in situ using Picarro GasScouter™ G4301 Gas Concentration Analyzer from April to November. Soil enzyme activities were highest in MIT followed by LIT, CK, and HIT. In addition, soil respiration rate and CH4 oxidation rate were the highest in MIT. CH₄ oxidation rates of LIT and CK were similar while the lowest value was noted in HIT. MIT showed the highest soil moisture, organic matter content and the lowest pH. We also conducted DNA based T-RFLP to determine the changes in community structure of bacteria and methanotrophs. The community structure of bacteria and methanotrophs were changed by thinning intensities. This suggests that change in abiotic factors by thinning affects soil extracellular enzyme activities and microbial communities, resulting in the change in greenhouse gas fluxes.