Morphological and physiological responses of critically endangered Acer catalpifolium to nitrogen deposition levels

Extensive industrial and agricultural emissions of reactive nitrogen (N) have led to severe N deposition and negative impacts on biodiversity. Acer catalpifolium is a critically endangered plant mainly distributed in N deposition hotspot of China, the influence of N deposition on morphological and physiological function of this species remains unclear. Therefore, a simulation experiment was conducted, wherein A. catalpifolium seedlings were subjected to different N deposition levels (0, 30, 60, 100, 150, and 200 kg N ha-1 y-1). The effects of N deposition on the morphological, photosynthesis, and fluorescence characteristics of A. catalpifolium were investigated. Results showed that height, biomass, crown, and basal diameter of A. catalpifolium were improved by N deposition, while vegetative growth was inhibited after the N input excess 100 kg N ha-1 y-1. Leaf gas exchange indices, photosynthetic light, CO2 response curve, fluorescence parameters and chlorophyll content were also improved by N addition but impeded by high levels of N deposition. In conclusion, the responses of A. catalpifolium to different levels of N deposition suggested that low and moderate N levels provided the necessary nutrient supply for plant growth. This study has major implications for the conservation and population recovery of A. catalpifolium and biodiversity protection in certain regions.