关键词: 干旱, 磷添加, 土壤酶, 热带雨林, 酶化学计量, 气候变化

Abstract: Aims Drought is a key stress factor affecting forest ecosystem, which causes direct physiological constraints on plants and soil microorganisms. As an important part of the global ecosystem, tropical rain forests are normally phosphorus limited and facing increasing drought stress. Mycorrhiza is an important way of continuous supply of soil carbon and nutrients, and soil enzyme activity is the key biological index to characterize the underground nutrient cycle, but how it responds to drought and phosphorus addition is still unclear. Methods In a tropical lowland rainforest of Ganzhaling Nature Reserve in Sanya, Hainan island, a two factorial manipulative experiment of throughfall reduction and phosphorus addition was established since May 2019. Combined with the in-situ incubation of mesocosms with different mesh sizes (1.45 mm, 0.053 mm, 0.001 mm), soil C, N, P cycle related enzyme activities and their relationship with soil physical and chemical properties were analyzed. Important findings Simulated drought inhibited soil enzyme activities, especially has significant negative impacts on hydrolase and oxidase related to carbon cycle. Phosphorus addition alleviated the phosphorus limitation of microorganisms, leading to changes of their investment strategy. Phosphorus addition alleviated the inhibition of drought on some hydrolases, but showed synergistic inhibition on oxidase. The mycorrhizae indirectly regulated soil enzyme activities, and the physical exclusion of root and hypha did not significantly affect the pattern of enzyme activity. This study reveals that the tropical forest soil microbial community has a strong ability to maintain a relatively stable investment of extracellular enzymes by regulating the community structure and internal storage, and further demonstrated the complex response mechanism of mycorrhizal mediated soil enzyme activity to drought. Our findings provided an important understanding for predicting the underground ecological process of tropical forest and its feedback to global change.

Key words: Drought, Phosphorus addition, Soil enzymes, Tropical rainforest, Enzyme stoichiometry, Global climate change