The Sites of Evaporation within Leaves
The Sites of Evaporation within Leaves
复制标题
DOI：
10.1104/pp.16.01605
复制
发表时间：
2017-03-01
期刊：
影响因子：
7.4
通讯作者：
Sack, Lawren
中科院分区：
文献类型：
--
作者：
Buckley, Thomas N.;John, Grace P.;Sack, Lawren
叶片内蒸发的位置尚不清楚，但它们几十年来一直引起人们的注意，因为它们对许多因素都有影响，包括叶片同位素富集型、叶肉水分状态的维持、气孔调节以及对测量的气孔和叶片水力传导性的解释。我们使用了一个木质部外水热耦合运输的空间显式模型MOFLO 2.0，绘制了净蒸发量在叶组织中的分布与解剖和环境参数的关系。我们的结果证实了早先的预测，即大多数蒸发发生在弱光和中等湿度下的表皮，但叶肉在叶中心被光吸收变暖时贡献很大，在高湿度下更是如此。我们还发现，束鞘提供了相当少的蒸发(在黑暗中占15%，在高光下占18%)，两栖类叶片的垂直中心支持净凝结，由光吸收引起的垂直温度梯度在不同物种之间差异超过10倍，达到0.3摄氏度。我们表明，几个依赖于蒸发地点的假设需要根据我们的发现进行修正，包括气孔和水力传导性的实验测量应该直接受到蒸发地点位置变化的影响。我们提出了一个新的概念模型来解释木质部外的混合相水分运输。这些结论对叶片水力学、气体交换、水分利用和同位素生理学的推断具有深远的影响。
The sites of evaporation within leaves are unknown, but they have drawn attention for decades due to their perceived implications for many factors, including patterns of leaf isotopic enrichment, the maintenance of mesophyll water status, stomatal regulation, and the interpretation of measured stomatal and leaf hydraulic conductances. We used a spatially explicit model of coupled water and heat transport outside the xylem, MOFLO 2.0, to map the distribution of net evaporation across leaf tissues in relation to anatomy and environmental parameters. Our results corroborate earlier predictions that most evaporation occurs from the epidermis at low light and moderate humidity but that the mesophyll contributes substantially when the leaf center is warmed by light absorption, and more so under high humidity. We also found that the bundle sheath provides a significant minority of evaporation (15% in darkness and 18% in high light), that the vertical center of amphistomatous leaves supports net condensation, and that vertical temperature gradients caused by light absorption vary over 10-fold across species, reaching 0.3 degrees C. We show that several hypotheses that depend on the evaporating sites require revision in light of our findings, including that experimental measurements of stomatal and hydraulic conductances should be affected directly by changes in the location of the evaporating sites. We propose a new conceptual model that accounts for mixed-phase water transport outside the xylem. These conclusions have far-reaching implications for inferences in leaf hydraulics, gas exchange, water use, and isotope physiology.