Effects of gaps in the forest canopy on soil microbial communities and enzyme activity in a Chinese pine forest

•Small (40-50 m2) canopy gaps promote soil microbial communities and enzyme activity.•Gram-positive bacteria and dissolved organic carbon levels drove the variations.•Enzyme activity was lowest in the large gaps (100-120 m2).•Fungal phospholipid fatty acids remained stable among the sites.

Gaps in the forest canopy play an important role in forest ecology, affecting biological dynamics, nutrient cycling, and plant succession. The influence of gap size on soil microbial communities and soil enzyme activity is poorly understood. Chinese pine (Pinus tabulaeformis) is one of the main afforestation species in northern China, and the creation of artificial gaps in Chinese pine forests is a common silvicultural practice to reduce forest density. We compared the microbial communities and the activity levels of several key enzymes in a Chinese forest among sites with closed canopies and canopies with small gaps (40-50 m2) and large gaps (100-120 m2) in October 2015, one year after the gaps were created. Soil samples from a depth of 0-10 cm were collected, and soil microbial community composition was evaluated using phospholipid fatty acid analysis. The activity levels of soil enzymes were also analyzed. Overall, the amounts of phospholipid fatty acids and the activity level of soil enzymes were highest in the sites with small gaps, followed by sites with closed canopies and sites with large gaps. Gram-positive bacteria were mainly responsible for the difference between microbial communities in sites with small gaps and sites with closed canopies. The activity levels of soil β-glucosidase and l-leucineaminopeptidase were also highest in sites with small gaps and lowest in those with large gaps. Soil acid phosphatase activity was similar in sites with small gaps and closed canopies and was lowest in sites with large gaps. Redundancy analysis indicated that dissolved organic carbon was the common driving factor affecting the variations in microbial communities and enzyme activity. Our results suggest that small gaps are beneficial for microbial communities. Further study of gap treatments is needed to determine the proper gap size for forest management.