Effect of Seasonal Variations on Soil Microbial, Extracellular Enzymes, and Ecological Stoichiometry in Tea Plantations.

Tea plantations are important agricultural ecosystems in karst areas, yet the seasonal dynamics of soil microbial communities, functional genes, and extracellular enzyme activities (EEA) under different management practices remain poorly understood. This study investigated organic (HY), pollution-free (TS), and conventional (XY) tea plantations in Weng'an County, Southwest China, during the spring (April) and autumn (August) tea seasons via metagenomics and stoichiometric analyses. Seasonal variations significantly altered the soil physicochemical properties (e.g., SOC, TN, and TP) and EEA (p < 0.05), with higher C-acquiring enzyme activity in autumn and elevated soil C:N:P ratios in spring. The soil extracellular enzyme stoichiometry (EES C:N:P) deviated from the theoretical 1:1:1 ratio, indicating that microbial metabolism was constrained by soil resource availability rather than homeostasis. Phosphorus limitation (vector angle > 45°) persisted across seasons, contradicting initial hypotheses, with acid phosphatase (ACP) activity and EES C:P identified as critical drivers. Random forest (RF) and structural equation modeling (SEM) revealed that the spring season had stronger impacts on microbial communities and functional genes, with the soil TN, C:N, NAG, ACP, and EES C:P ratios as key predictors. Compared with conventional practices, organic management enhances microbial diversity and functional redundancy, buffering seasonal fluctuations. These findings highlight the interplay between seasonal climatic shifts and agricultural practices regulating soil nutrient cycling and microbial adaptation. Strategic interventions-such as spring carbon supplementation, autumn organic phosphorus fertilization, and intercropping-are proposed to optimize microbial resilience and ecosystem stability in fragile karst tea plantations. This study provides novel insights into soil ecological stoichiometry and microbial metabolic strategies, offering a reference for the sustainable management of agroecosystems in karst areas.