Soil extracellular enzymes (SEEs) affect the decomposition of organic matter and microbial nutrient demand. However, the seasonal dynamics of SEE activity for differently aged plantations is still unclear. To analyze the seasonal variations of SEE activity and nutrient limitation for differently aged plantations, this study employed the “space-for-time substitution” method and Pinus massoniana plantations of varying ages (6, 13, 29, 38, and 57 years) in subtropical China to determine SEE activity and nutrient limitations in the growing and non-growing seasons. The results showed that SEE activity varied notably with the growth stage and season. In particular, β-1,4-glucosidase activity was higher in the growing season than in the non-growing season, while the opposite was observed for acid phosphatase and leucine-amino-peptidase activity. Acid phosphatase gradually increased with stand age, peaking in the 38-year plantation for the growing and non-growing seasons. Microbial carbon (C)-limitation was higher in the growing season and gradually decreased with forest stand development. Phosphorus (P)-limitation was higher in the growing season than in the non-growing season and was maximum in the 38-year plantation. Moreover, the physicochemical properties and microbial biomass explained the microbial C- and P-limitations, respectively. Compared to the non-growing season, the C- and P-limitations of different stand ages were stronger during the growing season, and the physicochemical properties and microbial biomass were important factors affecting their changes. The study reveals the balance status between soil microorganisms and nutrients in subtropical forest ecosystems and provides guidance for the development of afforestation strategies.

The coordinated enhancement of wood production and carbon sequestration in plantations is increasingly important for sustainable forest management and climate-change mitigation. However, quantitative evidence on how forest management can jointly improve these two functions remains limited. Based on 847 Pinus massoniana plantation plots (yielding 1184 consecutive-period observations) from China’s 7th–9th National Forest Inventories (covering 2004–2018), we quantified the degree of coordination between wood productivity and tree-layer carbon sequestration rate. Linear mixed-effects models, the piecewise structural equation model, and XGBoost-SHAP analyses were subsequently applied to identify the major drivers and threshold ranges of key stand factors. The results showed that mean carbon sequestration rate and wood productivity were 1.16 Mg/ha/yr and 4.17 m³/ha/yr, respectively. Among the examined management categories, plots with standing-volume harvest intensity < 0.15 (i.e., removing less than 15% of stand volume) showed the highest tree-layer carbon sequestration rate and wood productivity. Overall, wood productivity and tree-layer carbon sequestration rate showed broadly consistent responses across the examined management conditions, suggesting a generally high degree of coordination between the two functions. Stand structural attributes were the primary determinants of the degree of coordination, whereas management factors tended to strengthen this coordination both directly and indirectly through modifications of stand structure. Within the sampled range, a higher degree of coordination was associated with stand DBH values of 7.5–10.6 cm, stand density below 1071 trees/ha, stand age exceeding 29 years, and standing-volume harvest intensity approaching 0.12. These findings provide a quantitative basis for balancing timber production and tree-layer carbon sequestration, and offer practical implications for adaptive management of subtropical plantations under climate-mitigation and timber-supply objectives.