Abstract:Plant hydraulic traits can reflect the adaptability of plants to different water conditions. It is important to study the hydraulic traits of dominant plants in the special habitat of tropical coral islands for a deep understanding of the hydraulic adaptation strategies of tropical coral island plants, and for selecting suitable tree species for tropical coral island vegetation construction and restoration. Thus, the leaf and branch hydraulic traits of two representative dominant tree species in the habitat of tropical coral islands of China, i.e., Pisonia grandis and Scaevola sericea, were measured, and their hydraulic adaptation strategies were compared and analyzed. The results showed that the leaf embolism resistance, leaf turgor point and branch specific xylem conductivity of P. grandis were significantly higher than those of S. sericea, but the values of branch embolism resistance, leaf hydraulic conductance, sapwood density and leaf to stem area ratio were significantly lower than those of S. sericea. Furthermore, leaves of P. grandis were more resistant to embolism than branches, and were sensitive to water stress. Meanwhile, high water transport efficiency in branches of P. grandis provided sufficient water to ensure the high transpiration of the leaves. On the other hand, there was a significant hydraulic vulnerability segmentation between leaves and branches of S. sericea. The leaves of S. sericea could act as “safety valves” to protect branch hydraulic pathway from dysfunction. Pisonia grandis and S. sericea could adapt to the special habitats of tropical coral islands by coordinating the water transport efficiency and safety of leaves and branches and adopting different hydraulic strategies.

Abstract:To reveal the mechanisms of changing trend of mycorrhizal tree dominance under the environmental influence of increasing seasonal drought and nitrogen deposition in the lower subtropical monsoon evergreen broad-leaved forest, the hydraulic traits and nutrient traits of three ectomycorrhizal (EM), including Engelhardtia roxburghiana, Castanopsis chinensis and C. fissa, and three arbuscular mycorrhizal (AM) dominant trees, including Aporusa yunnanensis, Syzygium levinei and Craibiodendron scleranthum var. kwangtungense, were measured. The results showed that the leaf water potential at which 50% and 88% hydraulic conductance are lost (P50 and P88) and leaf turgor loss point (Ψtlp) of EM trees were lower than those of AM trees, while the sapwood specific hydraulic conductivity (KS), leaf specific hydraulic conductivity (KL), photosynthetic nitrogen use efficiency (PNUE) and photosynthetic phosphorus use efficiency (PPUE) of EM trees were higher than those of AM trees. The results suggested that EM trees have stronger drought resistance ability and higher water and nutrient use efficiency compared with AM trees. This might be the physiological mechanism of increasing dominance of EM trees while decreasing dominance of AM trees under the background of increasing drought and nitrogen deposition.