Response of the Soil Microbial Community to the Long-Term Effects of Thinning and its Key Roles in Tree Growth in a Natural Secondary Forest in Northeast China

Thinning is a major silvicultural management practice and can influence above- and belowground forest characteristics. However, the long-term effects of thinning on above- and belowground interactions in natural secondary forests are not clear. In this study, we conducted a thinning experiment in which we evaluated the changes in forest growth and mortality, soil properties and microbial characteristics in a natural secondary forest in Northeast China after thinning. The proportions of wood volume removal used were 0 (Con), 10% (LT), 20% (MT) and 30% (HT). Compared with Con, thinning significantly affected soil microbial biomass carbon (MOC), microbial biomass nitrogen (MON) and extracellular enzyme activity (EEA) but did not significantly affect microbial α -diversity indices. Furthermore, nonmetric multidimensional scaling (NMDS) showed that thinning significantly changed the soil microbial community structure at the operational taxonomic unit (OTU) level. Moreover, thinning not only promoted the growth of residual wood and decreased mortality but also improved soil quality. With increased thinning intensity, soil organic carbon (SOC), total nitrogen (TN), available nitrogen (aN), total phosphorus (TP), and available phosphorus (aP) increased, but the maximum SOC, TN and aN occurred in MT. The same pattern was observed for the growth indicators of trees. Redundancy analysis (RDA) showed that the soil microbial community structure was significantly correlated with soil nutrient factors and tree growth. These findings suggest that thinning significantly changes soil microbial community structure, resulting in soil nutrient accumulation and favorable soil conditions for the rapid growth of trees.