Department of Biology, California State University, Bakersfield, California 93311 USA.
Am J Bot. 2009 Aug;96(8):1445-53. doi: 10.3732/ajb.0800424. Epub 2009 Jul 10.
Mediterranean-type climate regions are highly biodiverse and predicted to be particularly sensitive to climate change. Shrubs of the mediterranean-type climate region of South Africa are highly threatened, and their response to water stress has been comparatively little studied. Resistance to water stress induced xylem cavitation (P(50)) and xylem specific hydraulic conductivity (K(s)) were measured in 15 shrub species from fynbos and succulent karoo communities of South Africa. Species displayed a fivefold variation in cavitation resistance (P(50) of -1.9 to -10.3 MPa) with succulent karoo species displaying greater interspecific variability in P(50) than fynbos species. Principal components analysis (including P(50), minimum seasonal water potential, K(s), and xylem density) showed the response to water stress in fynbos species to be similar to chaparral species from the mediterranean-type climate region of California. The data suggest convergence of community and species-specific water stress "strategies" between these mediterranean-type climate regions with respect to their xylem traits. On the basis of the current study and reported plant death and dieback in these regions, woody species within the fynbos may be more susceptible to climate warming and drying than those within the succulent karoo that appear to be utilizing more diverse xylem strategies in response to water stress.
地中海型气候区具有高度的生物多样性，预计对气候变化特别敏感。南非地中海型气候区的灌木受到高度威胁，其对水分胁迫的反应相对较少研究。本研究在南非的高山硬叶灌丛和肉质旱生灌丛群落中，测量了 15 种灌木对水分胁迫诱导的木质部空化（P(50)）和木质部比导率（K(s)）的抗性。研究发现，物种间的空化抗性（P(50)范围为-1.9 至-10.3 MPa）存在五倍的变化，肉质旱生灌丛物种的 P(50)比高山硬叶灌丛物种具有更大的种间变异性。主成分分析（包括 P(50)、最小季节性水势、K(s)和木质部密度）表明，高山硬叶灌丛物种对水分胁迫的反应与加利福尼亚地中海型气候区的灌丛物种相似。数据表明，这些地中海型气候区的群落和种间特定的水分胁迫“策略”在木质部特征上存在趋同。基于目前的研究和这些地区报道的植物死亡和衰退情况，高山硬叶灌丛中的木本物种可能比肉质旱生灌丛中的物种更容易受到气候变暖的影响，因为后者似乎利用了更多样化的木质部策略来应对水分胁迫。
