Department of Earth System Science, University of California, Irvine, CA 92697, USA.
Plant Cell Environ. 2011 Aug;34(8):1384-400. doi: 10.1111/j.1365-3040.2011.02339.x. Epub 2011 Jun 20.
Trees planted in urban landscapes in southern California are often exposed to an unusual combination of high atmospheric evaporative demand and moist soil conditions caused by irrigation. The water relations of species transplanted into these conditions are uncertain. We investigated the water relations of coast redwood (Sequoia sempervirens) planted in the urbanized semi-arid Los Angeles Basin, where it often experiences leaf chlorosis and senescence. We measured the sap flux (J(O)) and hydraulic properties of irrigated trees at three sites in the Los Angeles region. We observed relatively strong stomatal regulation in response to atmospheric vapour pressure deficit (D; J(O) saturated at D < 1 kPa), and a linear response of J(O) to photosynthetically active radiation. Total tree water use by coast redwood was relatively low, with plot-level transpiration rates below 1 mm d(-1) . There was some evidence of xylem cavitation during the summer, which appeared to be reversed in fall and early winter. We conclude that water stress was not a direct factor in causing leaf chlorosis and senescence as has been proposed. Instead, the relatively strong stomatal control that is adaptive in the native habitat of coast redwood may lead to carbon limitation and other stresses in semi-arid, irrigated habitats.
在加利福尼亚州南部的城市景观中种植的树木经常暴露在高大气蒸发需求和灌溉引起的潮湿土壤条件的不寻常组合中。移植到这些条件下的物种的水分关系是不确定的。我们研究了种植在城市化半干旱洛杉矶盆地中的海岸红杉（Sequoia sempervirens）的水分关系，在那里它经常经历叶片黄化和衰老。我们在洛杉矶地区的三个地点测量了灌溉树木的 sap 通量（J(O)）和水力特性。我们观察到相对较强的气孔调节响应大气蒸气压亏缺（D；J(O)在 D < 1 kPa 时饱和），以及 J(O)对光合有效辐射的线性响应。海岸红杉的总树木耗水量相对较低，每个样地的蒸腾速率低于 1 mm d(-1)。在夏季有一些木质部空化的证据，这似乎在秋季和初冬得到了逆转。我们的结论是，正如所提出的那样，水分胁迫不是导致叶片黄化和衰老的直接因素。相反，在海岸红杉的原生栖息地中适应性较强的气孔控制可能会导致在半干旱、灌溉的栖息地中出现碳限制和其他压力。
