Objective Plant photosynthesis is a key physiological process for carbon sequestration in forest ecosystems. Here, we studied the effects of nitrogen deposition on leaf traits and photosynthetic parameters of dominant tree species in tropical forest ecosystems, aiming to lay a foundation for revealing the response process of tropical trees to exogenous nitrogen inputs and assessing the change of forest carbon sequestration potential in the context of nitrogen deposition.
Method A nitrogen addition experiment was conducted for nine years to analyze the effects of three nitrogen addition levels on important leaf traits and photosynthetic parameters of two dominant tree species (i.e., Cryptocarya chinensis and Gironniera subaequalis) in the tropical montane rainforest of Jianfengling, Hainan Province of southern China.
Result Leaf traits and photosynthetic parameters showed significant differences between species. For plant leaf traits, nitrogen addition significantly increased specific leaf area of C. chinensis and nitrogen to phosphorus ratio of both species, decreased chlorophyll content, and altered leaf nutrient content to some extent. For plant photosynthesis, nitrogen addition tended to promote transpiration rate and stomatal conductance, but did not significantly affect photosynthetic parameters (including net photosynthetic rate, intercellular CO2 concentration, maximum carboxylation rate, and maximum electron transport rate).
Conclusion Overall, 9 years of nitrogen addition has not yet significantly altered leaf photosynthetic process of two dominant tree species in Hainan tropical montane rainforest. Based on extensive field monitoring, revealing the response mechanisms of tropical trees to nitrogen addition from the perspective of leaf functional traits-photosynthesis coupling is the next step of our research focus.
DownLoad: