Responses of plant functional traits to environmental changes in tropical cloud forest

Studying the response of plant functional traits to environmental changes is helpful for understanding the plant adaptation strategies to the environment. In the report， the tropical cloud forest in Bawangling Area of Hainan Tropical Rain Forest National Park was taken as the research object， the community investigation was conducted on 21 woody plants with DBH ≥5 cm in 20 m×20 m fixed plots in 2011 and 2021， the plant functional traits and environmental factors at individual， species and community levels were measured， and the changes in plant functional traits and environmental conditions were analyzed， the influence of environmental factors on functional traits was explored. The results showed that：（1） Compared with that in 2011， the contents of total nitrogen （TN） and available nitrogen （AN） in soil of tropical cloud forest were significantly increased in 2021， while the contents of organic matter （SOM）， total phosphorus （TP） and available phosphorus （AP） were significantly decreased. The maximum air temperature showed an upward trend， while the average air relative humidity and the minimum air relative humidity showed a downward trend. Based on the principal component analysis of environmental factors，the environmental factors with large load value in 2011 were soil total nitrogen， soil total phosphorus， soil available nitrogen and minimum air relative humidity， while the environmental factors with large load value in 2021 were soil organic matter， soil total phosphorus， maximum air temperature and minimum air relative humidity. （2） Compared with that in 2011， the chlorophyll content and leaf thickness of plants at individual level increased significantly in 2021， while the specific leaf area decreased significantly；leaf thickness， chlorophyll content， stem total nitrogen content and leaf total nitrogen content increased significantly at the species level，while stem soluble sugar content and leaf total phosphorus content decreased significantly. Chlorophyll content， leaf thickness， stem total nitrogen content， stem total phosphorus content and leaf total nitrogen content increased significantly at the community level， while stem density， stem soluble sugar content and leaf total phosphorus content decreased significantly. （3） Multiple stepwise regression analysis suggest that soil nutrient content （such as soil organic matter，total phosphorus content， available nitrogen content， etc.） and climate factors （such as maximum air temperature， minimum air relative humidity， etc.） jointly affect the changes of plant individual， species and community functional traits， and soil nutrient factors play a significant role. The intensification of soil P stress is the key factor affecting the functional traits of each community.