【摘要】 桂西南喀斯特地区生物多样性丰富、特有种多,同时也是石漠化问题较为严重的区域。由于该喀斯特地区土层浅薄、岩石裸露、表层储水能力差,植物在干旱季节经常会受到水分胁迫。植物水力学特征不仅是探讨喀斯特地区植物的生理生态适应性的关键,还能够为石漠化地区的植被恢复提供重要参考。该研究测定了桂西南喀斯特季雨林17种代表性木本植物(包括不同生活型、叶片习性和生境)的木质部脆弱性曲线、最低水势、叶片膨压丧失点和边材密度等水力性状,结果发现:(1)喀斯特植物木质部导水率丧失50%时的水势值(P50)的种间差异较大(–0.51––2.51MPa),其中常绿种的抗栓塞能力比落叶种强;(2)喀斯特植物的木质部水力安全边界值(最低水势与P50之间的差值)的均值为0.36 MPa,说明喀斯特森林植物在自然最低水势状况下木质部发生栓塞的程度较高;但是不同植物种间存在显著差异,这可能与喀斯特峰丛洼地生境的复杂性以及物种不同的抗旱策略有关;(3)由于喀斯特植物水分适应机制的多样化,导致木质部水力安全边界与叶片膨压丧失点、边材密度的相关性并不显著。在区域气候干热化的背景下,结合喀斯特植物的栓塞脆弱性和长期水势监测(尤其极端干旱事件)分析它们的水力安全,对预测未来喀斯特森林物种分布和群落动态具有重要的指示作用。更多还原

【Abstract】 Aims Tropical seasonal rain forest of the karst landscape in southwestern Guangxi is one of the global biodiversity hotspots, with its habitats characterized with large exposed boulders, shallow and patchy soils, and cascading streams. As a result, plants in the karst landscapes experience frequent drought due to limited soil water holding capacity. In this study, we investigate the hydraulic characteristics of woody species in this drought-prone environment for sound conservation of plants in the fragile forests as well as through restoration actions.Methods We measured xylem vulnerability curves, minimum xylem water potential(Ψstem-min), sapwood density and leaf turgor loss point of 17 typical woody plant species that co-occur in a tropical seasonal rain forest. We compared cavitation-resistance and hydraulic safety margins among the species and/or by plant groups. In addition, we analyzed the relationships between hydraulic safety margins and other hydraulic characteristics.Important findings We found large inter-species variations in xylem water potential at 50% of hydraulic conductivity(P50 ranged from –0.51 to –2.51 MPa), with evergreen species showing more negative P50 than deciduous species. The hydraulic safety margin(HSM), calculated as the difference between Ψstem-min and P50(Ψstem-min –P50), has been widely used to quantify the degree of hydraulic risk under droughts. The average HSM of the 17 woody species was 0.36 MPa, indicating a high hydraulic risk in this forest during the dry season. However, there existed significant differences in HSM among species. Interestingly, there was no significant correlation between HSM and other key hydraulic characteristics, likely because of different hydraulic strategies under drought stress.This study provides evidences of different hydraulic risks of the common species in response to droughts and highlights the importance of long-term monitoring of water potential for conservation of the plants, especially in extreme drought events.更多还原