关键词: 胞外酶, 矢量长度, 矢量角度, 碳限制, 磷限制, 幼龄林

Abstract: Pruning is one of the commonly used tending practices in plantation management. However, the short-term effects of pruning on soil microbial dynamics remain poorly understood, which constrains the development of precise tending practices. In this study, we set four pruning treatments in a 5-year-old Pinus massoniana plantation at Fubo Forest Farm in the Guangxi Zhuang Autonomous Region, including no pruning (control, CK), light pruning (removal of branches below one-third of the dominant tree height; 1/3 pruning), moderate pruning (removal of branches below one-half of the dominant tree height; 1/2 pruning), and heavy pruning (removal of branches below two-thirds of the dominant tree height; 2/3 pruning). Soil physicochemical properties, microbial biomass, and extracellular enzyme activities were measured, and ecoenzymatic stoichiometric ratios and vector characteristics were calculated. The results showed that: (1) Pruning significantly affected soil enzyme activities and ecoenzymatic stoichiometric characteristics. Under the 1/3 pruning treatment, β-1,4-glucosidase activity, the ratio of carbon (C)-acquiring to nitrogen (N)-acquiring enzyme activities, and the ratio of C-acquiring to phosphorus (P)-acquiring enzyme activities were the highest, being 66.59%, 28.70%, and 15.56% higher than that in CK, respectively. In contrast, under the 1/3 pruning treatment, the activities of the N-acquiring enzymes β-1,4-N-acetylglucosaminidase and leucine aminopeptidase, together with the ratio of N-acquiring to P-acquiring enzyme activities, were the lowest, being 15.75%, 28.48%, and 9.64% lower than that in CK, respectively. (2) Pruning significantly affected vector angle (VA) and vector length (VL), both of which were significantly higher under the 1/3 pruning treatment than under the other treatments. Under all treatments, VA and VL were greater than 45° and 1, respectively, and VA increased with increasing VL. (3) Redundancy analysis showed that soil microbial biomass C, the microbial biomass C/N ratio, and nitrate significantly affected ecoenzymatic stoichiometric characteristics and microbial nutrient limitation. Partial least squares path modeling further showed that soil inorganic N and total potassium exerted indirect positive effects on VA by positively regulating microbial biomass. In conclusion, light pruning increased the activities of soil C- and P-acquiring enzymes, but simultaneously intensified microbial nutrient limitation. Soil microbial biomass played a mediating role in  the effects of soil chemical properties on microbial P limitation. These findings provide a theoretical reference for selecting an appropriate pruning intensity in P. massoniana plantations in the southern subtropical region of China.

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