Moderate stand density alleviates microbial phosphorus limitation in tropical Pinus kesiya var. langbianensis plantations

Soil ecoenzymatic stoichiometry is a crucial indicator of microbial nutrient demand and metabolic limitations. Stoichiometric models can be used to estimate microbial carbon (C) use efficiency (CUE ST ), an important parameter for evaluating microbial involvement in soil C-cycling. Although stand density management is a key component in forest management, its effects on ecoenzymatic stoichiometry, microbial metabolic limitations, and CUE remain uncertain. This study collected soil samples from four stand densities (LD, 750 ± 14 trees·ha −1 ; LED, 883 ± 17 trees·ha −1 ; MD, 1075 ± 14 trees·ha −1 ; HD, 1208 ± 8 trees·ha −1 ) in three seasons (dry, early rainy, rainy) in tropical Pinus kesiya var. langbianensis plantations. We measured β-glucosidase (BG), N-acetyl-β- D -glucosaminidase (NAG), leucine aminopeptidase (LAP), and acid phosphatase (ACP) activities. We further identified potential factors influencing microbial metabolic limitations and CUE ST . Microbial metabolism was limited by phosphorus (P). P-limitation was significantly alleviated in MD, being 5.12%-7.74% lower than in LD, LED, and HD. Variations in microbial metabolic limitations were primarily associated with microbial biomass carbon (MBC), MBP, dissolved organic carbon (DOC), and nitrate nitrogen (NO 3 - -N). CUE ST was highest in MD, exceeding other stands by 2.51%-8.50%. CUE ST was directly influenced by soil C:N and C:P. The MD (moderate density) enhanced microbial nutrient utilization and promoted soil C sequestration in the 36-year-old Pinus kesiya var. langbianensis plantations. This study highlights the importance of stand density management for soil nutrient cycling and microbial metabolic processes in plantation ecosystems.