Bush Susan E, Pataki Diane E, Hultine Kevin R, West Adam G, Sperry John S, Ehleringer James R
Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.
Oecologia. 2008 May;156(1):13-20. doi: 10.1007/s00442-008-0966-5. Epub 2008 Feb 13.
Plant transpiration is strongly constrained by hydraulic architecture, which determines the critical threshold for cavitation. Because species vary greatly in vulnerability to cavitation, hydraulic limits to transpiration and stomatal conductance have not generally been incorporated into ecological and climate models. We measured sap flow, leaf transpiration, and vulnerability to cavitation of a variety of tree species in a well-irrigated but semi-arid urban environment in order to evaluate the generality of stomatal responses to high atmospheric vapor pressure deficit (D). We found evidence of broad patterns of stomatal responses to humidity based on systematic differences in vulnerability to cavitation. Ring-porous taxa consistently had vulnerable xylem and showed strong regulation of transpiration in response to D, while diffuse-porous taxa were less vulnerable and transpiration increased nearly linearly with D. These results correspond well to patterns in the distribution of the taxa, such as the prevalence of diffuse-porous species in riparian ecosystems, and also provide a means of representing maximum transpiration rates at varying D in broad categories of trees.
植物蒸腾作用受到水力结构的强烈限制，而水力结构决定了空化的临界阈值。由于不同物种对空化的脆弱性差异很大，因此蒸腾作用和气孔导度的水力限制一般未被纳入生态和气候模型中。我们在一个灌溉良好但半干旱的城市环境中，测量了多种树种的液流、叶片蒸腾作用以及对空化的脆弱性，以评估气孔对高大气水汽压差（D）响应的普遍性。我们基于对空化脆弱性的系统差异，发现了气孔对湿度响应的广泛模式的证据。环孔类群的木质部始终较为脆弱，并且对D表现出强烈的蒸腾调节作用，而散孔类群则较不易受影响，蒸腾作用随D几乎呈线性增加。这些结果与类群分布模式非常吻合，例如河岸生态系统中散孔物种的普遍存在，并且还提供了一种在不同大类树木中表示不同D值下最大蒸腾速率的方法。
