Thinning intensity affects microbial functional diversity and enzymatic activities associated with litter decomposition in a Chinese fir plantation

Microbial functional diversity and enzymatic activities are critical to maintaining material circulation during litter decomposition in forests. Thinning, an important and widely used silvicultural treatment, changes the microclimate and promotes forest renewal. However, how thinning affects microbial functional diversity and enzymatic activities during litter decomposition remains poorly understood. We conducted thinning treatments in a Chinese fir plantation in a subtropical region of China with four levels of tree stem removal (0, 30, 50, and 70%), each with three replicates, and the effects of thinning on microbial functional diversity and enzymatic activities were studied 7 years after treatment by collecting litter samples four times over a 1-year period. Microbial functional diversity and enzymatic activities were analyzed using Biolog Ecoplates (Biolog Inc., Hayward, CA, USA) based on the utilization of 31 carbon substrates. Total microbial abundance during litter decomposition was lower after the thinning treatments than without thinning. Microbial functional diversity did not differ significantly during litter decomposition, but the types of microbial carbon-source utilization did differ significantly with the thinning treatments. Microbial cellulase and invertase activities during litter decomposition were significantly higher under the thinning treatments due to changes in the litter carbon concentration and the ratios of carbon and lignin to nitrogen. The present study demonstrated the important influence of thinning on microbial activities during litter decomposition. Moderate-intensity thinning may maximize vegetation diversity and, in turn, increase the available substrate sources for microbial organisms in litter and promote nutrient cycling in forest ecosystems.