Abstract: Aims It is of great significance to explore soil extracellular enzyme activity and its stoichiometry to understand soil nutrient availability and changes in the nutrient requirements of microorganisms. Subtropical forest ecosystems have a high level of plant productivity, but the availability of phosphorus (P) in soil is low due to severe soil weathering. Under climate change (i.e., warming, elevated CO2 concentration), plant productivity is predicted to increase, which will increase the input of leaf litter. However, it is still unclear whether the effect of increasing litter input on soil enzyme activity and its stoichiometry is affected by soil phosphorus availability in the future. Methods This study investigated the effects of the addition of three kinds of litters (Pinus massoniana, Michelia macclurei and Liquidambar formosa) with different quality (characterized by different leaf carbon:nitrogen or carbon:phosphorus) and P on soil properties and enzyme activities in subtropical low-P soils. By analyzing the enzyme stoichiometric ratio, vector length (VL), and vector angle (VA), the relative nutrient limitation of soil microorganisms and the key regulatory factors were explored. Important findings The results showed that litter addition increased β-N-acetyl-glucosaminidase and acid phosphatase (ACP) activities. Moreover, we found that the addition of litter significantly increased the VL and VA in the order of M. macclurei > L. formosana > P. massoniana. The results indicated that litter addition could change the nutrient restriction status of soil microorganisms, and the degree of influence was related to the quality of litter. Compared with the addition of litter alone, the addition of litter combined with P significantly increased the amount of available P, and reduced ACP activity and the VA, suggesting that P addition could help alleviate the P limitation of soil microorganisms under the input of litter. Redundancy analysis results showed that the soil carbon/nitrogen ratio, dissolved organic carbon, and available P were the main factors affecting enzyme activities and their stoichiometric changes. In conclusion, our study found that the response of soil microbial nutrient limitation to litter input in subtropical forest was not only affected by litter quality, but also regulated by soil P availability. This study provides a theoretical reference for the response of microbial nutrient acquisition strategies to different litter inputs and P additions in subtropical forests under future climate change, and is conducive to improving our understanding of the soil biogeochemical cycle in subtropical low phosphorus forest ecosystems.

Key words: litter, phosphorus addition, soil enzyme activity, enzymatic stoichiometry, nutrient limitation