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Coral reefs are severely threatened by global and local disturbances that can shift reefs from coral to algal dominance. Coral-macroalgae competition is expected to exacerbate coral decline as the interactions increase in frequency. Whereas numerous studies over the last decade have aimed to characterize the interactions and impacts on coral growth and physiology, the underlying mechanisms remain controversial. This study tested the impact of different macroalgal species, densities, and contact status with corals on the physiological response of corals in Sanya Reefs. The results revealed that direct contact with increasing densities of fleshy macroalgae had a negative impact on the photosynthesis, growth rate, and tissue biomass of the two common corals. However, calcified macroalgae did not significantly affect the corals, regardless of whether there was direct contact or not. Under the same conditions, Acropora intermedia appeared to be more susceptible to fleshy macroalgae compared to Porites lutea. This suggested that different corals varied in their susceptibility to various macroalgae. Additionally, the results of the generalized linear mixed model revealed that macroalgal species and contact status with corals were the most important predictors of the impacts of macroalgae on corals, and macroalgal density was another nonnegligible parameter. Overall, macroalgae may have caused a potential functional shift in the composition of coral assemblages on the Sanya reefs by further reducing the already depauperate reef-building coral populations. The negative impacts of macroalgae in Sanya Reefs may serve as an early warning that the persistence of the invaluable ecological functions provided by coral reefs will be increasingly threatened throughout the South China Sea. Our findings could contribute to improving the scientific and effective management practices, fostering sustainable coral reef development in China and beyond.

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.

Acer amplum subsp. catalpifolium is a critically endangered, native deciduous broad-leaved tree species mainly distributed in the rainy zone of west China. Acid rain is a frequent phenomenon in this region and its impact on regional forests, especially for susceptible species have major implications on community stability and biodiversity conservation. To understand the basic physiological responses of A. amplum subsp. catalpifolium to acid rain, a simulation experiment spanning 18 months was conducted. The aim is to determine the effects of acidity levels (pH 2.5, 3.5, and 4.5), chemical composition (H2SO4: HNO3 ratio of 7.5:1 and 5:4.1, respectively), and deposition patterns (soil addition and leaf spraying modes) on photosynthetic performance and stress status of A. amplum subsp. catalpifolium The results showed that simulated acid rain can enhance the peak photosynthetic rate (Pn) and stomatal conductance (Cs) in the diurnal variation of A. amplum subsp. catalpifolium under soil addition mode, and it is attributed to the increased net photosynthetic rate at the light saturation point (Amax), net photosynthetic rate at saturating CO2 concentration (Pmax) and various chlorophyll fluorescence parameters (ΦPSII, Fv/Fm, Fv/F0, and qP). On the contrary, the photosynthetic performance of A. amplum subsp. catalpifolium was significantly inhibited by acid rain under leaf spraying mode, with increased dark respiration rate (Rd) and photorespiration rate (Rp). The reduction levels in Amax and Pmax was higher in the nitric based acid rain compared to sulfuric acid dominant acid rain. In general, improved nutrient availability brought about by acid rain on soil promoted the photosynthetic performance of A. amplum subsp. catalpifolium. Meanwhile, acid rain in direct contact with the leaves negatively affects leaf performance and chemical makeup. Therefore, acid rain patterns (such as fog or snow) in direct contact with leaves should be accounted for in the protection of A. amplum subsp. catalpifolium.

As a critically endangered species, Acer catalpifolium Rehd. is included in the wild plants with extremely small populations (WPESP) rescue and protection plan. Understanding of the responses of A. catalpifolium to various resource and environment conditions could help identify potentially suitable environments for its conservation. We used an orthogonal experiment design to evaluate the growth, morphological and physiological responses of A. catalpifolium and a widespread same-genus species A. mono to diverse water and light stresses. The results showed that a 75% soil water holding capacity and moderate shade are suitable for seedling growth. Drought and shade had significant negative effects on plant growth, biomass accumulation, and physiological functions. Lowering specific leaf areas (SLA), increasing root biomass allocation, and pigment content were the main strategies for enhancing water and light capturing abilities to acclimate to the limited ambient resources. The general plasticity index of plant growth, biomass, and physiological characteristics were higher in A. mono than in A. catalpifolium. We also explored the suitable light and water requirements for A. catalpifolium seedling growth. Our research would be useful for population regeneration and could aid in biodiversity conservation of Acer species. Keywords: Acer catalpifolium Rehd, Drought, Shade, Wild plants with extremely small populations (WPESP)