Smith W K, Geller G N
Botany Department, University of Wyoming, 82071, Laramie, Wyoming, USA.
Oecologia. 1979 Jul;41(1):109-122. doi: 10.1007/BF00344841.
The influence of elevational changes on plant transpiration was evaluated using leaf energy balance equations and well-known elevational changes in the physical parameters that influence water vapor diffusion. Simulated transpirational fluxes for large leaves with low and high stomatal resistances to water vapor diffusion were compared to small leaves with identical stomatal resistances at elevations ranging from sea level to 4 km. The specific influence of various air temperature lapse rates was also tested. Validation of the simulated results was accomplished by comparing actual field measurements taken at a low elevation (300 m) desert site with similar measurements for a high elevation (2,560 m) mountain research site. Close agreement was observed between predicted and measured values of transpiration for the environmental and leaf parameters tested.Substantial increases in solar irradiation and the diffusion coefficient for water vapor in air (D ) occurred with increasing elevation, while air and leaf temperatures, the water vapor concentration difference between the leaf and air, longwave irradiation, and the thermal conductivity coefficient for heat in air decreased with increasing elevation. These changes resulted in temperatures for sunlit leaves that were further above air temperature at higher elevations, especially for large leaves. For large leaves with low stomatal resistances, transpirational fluxes for low-elevation desert plants were close to those predicted for high-elevation plants even though the sunlit leaf temperatures of these mountain plants were over 10°C cooler. Simulating conditions with a low air temperature lapse rate (0.003° C m and 0.004° C m) resulted in predicted transpirational fluxes that were greater than those calculated for the desert site. Transpiration for smaller leaves decreased with elevation for all lapse rates tested (0.003° C m to 0.010° C m). However, transpirational fluxes at higher elevations were considerably greater than expected for all leaves, especially larger leaves, due to the strong influence of increased solar heating and a greater D . These results are discussed in terms of similarities in leaf structure and plant habit observed among low-elevation desert plants and high-elevation alpine and subalpine plants.
利用叶片能量平衡方程以及影响水汽扩散的物理参数中广为人知的海拔变化，评估了海拔变化对植物蒸腾作用的影响。在海拔从海平面到4千米的范围内，将具有低和高气孔对水汽扩散阻力的大叶模拟蒸腾通量与具有相同气孔阻力的小叶进行了比较。还测试了各种气温递减率的具体影响。通过将在低海拔（300米）沙漠站点进行的实际野外测量结果与高海拔（2560米）山区研究站点的类似测量结果进行比较，完成了对模拟结果的验证。在所测试的环境和叶片参数方面，观察到蒸腾作用的预测值与测量值之间有密切的一致性。随着海拔升高，太阳辐射和空气中水汽的扩散系数（D）大幅增加，而空气和叶片温度、叶片与空气之间的水汽浓度差、长波辐射以及空气中热量的导热系数则随着海拔升高而降低。这些变化导致在较高海拔处，受阳光照射的叶片温度比气温高出更多，尤其是对于大叶而言。对于气孔阻力低的大叶，低海拔沙漠植物的蒸腾通量与高海拔植物的预测值相近，尽管这些山区植物受阳光照射的叶片温度要低10°C以上。模拟低气温递减率（0.003°C/m和0.004°C/m）的条件导致预测的蒸腾通量大于沙漠站点计算得出的通量。对于所有测试的递减率（0.003°C/m至0.010°C/m），较小叶片的蒸腾作用随海拔升高而降低。然而，由于太阳加热增加和D增大的强烈影响，在较高海拔处所有叶片的蒸腾通量都比预期的要大得多，尤其是大叶。根据在低海拔沙漠植物与高海拔高山和亚高山植物之间观察到的叶片结构和植物习性的相似性，对这些结果进行了讨论。
