Abstract: Soil enzyme activity and its stoichiometric characteristics are important indicators for characterizing the balance of microbial metabolism and soil nutrient supply. However, the stoichiometric characteristics of soil enzymes and the differences in microbial nutrient limitations among different forest stand types under the background of rapid urbanization remain unclear. We analyzed soil enzyme stoichiometry and its influencing factors across coniferous forest (pure Pinus massoniana forest), broad-leaved forest (camphor forest or oak forest), mixed coniferous and broad-leaved forest in both urban areas (Turtle Mountain, Yujia Mountain and Lion Mountain), and suburban areas (Jiufeng Mountain, Qinglong Mountain, and Jiuzhen Mountain) of Wuhan. We further explored the nutrient limitation of soil microorganisms. The activities of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosidase (NAG), leucine aminopeptidyase (LAP), and acid phosphatase (ACP) were higher in the urban areas than those in the suburban areas, while the activities of BG and ACP in broad-leaved forests were significantly higher than those in coniferous forests and mixed coniferous and broad-leaved forests. The soil enzyme vector angles (VA) of all stands were >45°, indicating that microorganisms were generally phosphorus-limited, with the degree of limitation being higher in the suburb aeras. Redundancy analysis showed that soil available nutrients (available N and P), C∶N, and MBN were the main factors affecting soil enzyme activities and stoichiometric ratios. In conclusion, urbanization may regulate microbial metabolism and enzymatic stoichiometric changes by altering the availability of forest soil nutrients and microbial biomass, thereby influencing soil nutrient cycle. It is suggested that in future urban forest management, native broad-leaved tree species should be appropriately increased to optimize stand structure, and that fertilizers should be applied reasonably to alleviate soil P limitation in suburban forests, thereby promoting sustainable management of urban forests.

Key words: soil enzyme activity, enzyme stoichiometry, urbanization, stand type, nutrient limitation