The main objective of this study was to investigate the response of soil enzyme activity and enzyme stoichiometry to changes in forest stand age, in order to provide theoretical and data support for understanding the interaction process and mechanism between soil physicochemical properties, enzyme activity, and stoichiometry in southern subtropical Chinese fir plantations at different stand ages (6, 13, 25, 30, 35, and 40 years). Additionally, the effects of soil environmental factors on enzyme activities and stoichiometric characteristics were examined by using correlation, stepwise regression, and redundancy analyses. The results showed that soil water content (SWC), carbon (C), and nutrient content significantly decreased in the middle stand age (13 years). However, the activities of β-glucosidase (BG), N-acetylaminoglucosidase (NAG), and acid phosphatase (ACP) increased. Redundancy analysis (RDA) indicated that the soil carbon: nitrogen ratio (C∶N), total nitrogen (TN), and ammonium nitrogen (NH4+) content were the main environmental factors driving the changes in soil enzyme activities in the plantations with stand development. Stand age had a significant influence on the soil enzyme C∶N (eC∶N), carbon∶phosphorus (eC∶P), nitrogen∶phosphorus (eN∶P), soil carbon quality (CQI), and microbial resource limitation in the plantations. Phosphorus was the most limiting nutrient element in the plantations of different stand ages in the southern subtropics. Changes in soil enzyme stoichiometric characteristics of varying stand ages were mainly regulated by SWC, TN, nitrate nitrogen (NO3-), and NH4+ contents in different forest ages. Changes in soil physicochemical properties induced by forest stand age variations were the main driving factor for the changes in soil enzyme activities and enzyme stoichiometric characteristics in Chinese fir plantations. The results of this study provide a reference for the management of Chinese fir plantations in South China. Appropriate application of N and P fertilizers in the fast-growing stage, along with P fertilizer in other stages, could help to promote the improvement and restoration of nutrients. This contributed to enhancing forest productivity and the enhancement of ecosystem service functions.
Keywords: Cunninghamia lanceolata; enzyme activity; extracellular enzyme stoichiometry; metabolic limitation; stand age.