Close-to-nature management alleviated microbial P limitation in middle-aged Masson pine plantations: Evidence derived from ecoenzymatic stoichiometry

Abstract

Close-to-nature management (CTNM) is an essential strategy for improving the structure and quality of plantations. However, the effects of CTNM on soil microbial resource limitation remain poorly understood. In this study, we examined soils from Masson pine plantations in three different stand stages after 12 years of CTNM. We measured the activities of six extracellular enzymes: β-1,4-glucosidase, β-1,4-xylosidase, cellobiohydrolase, L-leucine aminopeptidase, β-1,4-N-acetylglucosaminidase, and acid phosphatase. Additionally, we analyzed extracellular enzyme stoichiometry (EES), including vector length and angle. We also identified factors that may affect microbial resource limitation. Our results indicated that microorganisms in Masson pine plantations were primarily limited by phosphorus (P). CTNM significantly enhanced the activities of the six extracellular enzymes, alleviating microbial P limitation, but also increased nitrogen (N) limitation in middle-aged stands. Variations in enzyme activities and EES were most strongly influenced by soil nutrient content, followed by physical factors, with vegetation variables having the least impact. Microbial P limitation was negatively correlated with soil organic carbon, total N, available N, and capillary porosity, and positively correlated with the average diameter at breast height, tree height, and biomass of the shrub-herb community beneath the trees. Furthermore, microbial P limitation was directly influenced by soil total and available nutrients. The effects of vegetation and physical parameters on microbial P limitation were indirect, primarily through their impact on soil nutrient availability. Our research highlights the potential of CTNM to alleviate phosphorus limitations in microbial communities. We recommend the repeated implementation of CTNM, along with anthropogenic nitrogen addition and the introduction of nitrogen-fixing species, to enhance its effectiveness in alleviating microbial resource limitations in Masson pine plantations.