中国热带珊瑚岛优势木本植物抗风桐和草海桐的水分适应策略解析

Hydraulic Adaptation Strategies of Dominant Woody Plants Pisonia grandis and Scaevola sericea on Tropical Coral Islands of China

摘要:

植物水力性状能够反映植物对不同水分条件的适应能力，研究热带珊瑚岛特殊生境下优势植物的水力功能特征对深入理解热带珊瑚岛植物的水分适应策略，从而选择热带珊瑚岛植被构建和恢复的适生物种具有重要意义。该研究以中国热带珊瑚岛生境中2种优势适生木本植物：抗风桐(Pisonia grandis)和草海桐(Scaevola sericea)为研究对象，比较了其叶片和枝条的水力性状，并分析了其水分适应策略。结果表明, 抗风桐的叶片栓塞抗性、枝条边材比导水率和叶片膨压丧失点显著高于草海桐，而枝条栓塞抗性、叶片导水率、边材密度和叶面积边材面积比均显著低于草海桐。抗风桐的叶片具有比枝条更强的抗栓塞能力，对水分胁迫敏感，但同时选择以高效的枝干水分运输来满足叶片高蒸腾需求的充足供水。草海桐枝条与叶片则存在水力脆弱性分区，在面临水分胁迫时叶片充当“安全阀”以保证枝干木质部的水力安全。抗风桐与草海桐能够通过协调叶片与枝条水力性状采取不同的水分适应策略，从而更好地适应热带珊瑚岛的特殊生境。

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.