Centre for Ecosystem Studies, Forest Ecology and Forest Management, Wageningen University, Wageningen 6700AA, The Netherlands.
Tree Physiol. 2011 Jul;31(7):740-50. doi: 10.1093/treephys/tpr067.
A conceptual model was tested for explaining environmental and physiological effects on leaf gas exchange in the deciduous dry tropical woodland tree Boswellia papyrifera (Del.) Hochst. For this species we aimed at (i) understanding diurnal patterns in leaf gas exchange, (ii) exploring cause-effect relationships among external environment, internal physiology and leaf gas exchange, and (iii) exploring site differences in leaf gas exchange in response to environmental variables. Diurnal courses in gas exchange, underlying physiological traits and environmental variables were measured for 90 trees on consecutive days at two contrasting areas, one at high and the other at low altitude. Assimilation was highest in the morning and slightly decreased during the day. In contrast, transpiration increased from early morning to midday, mainly in response to an increasing vapor pressure deficit (VPD) and gradual stomatal closure. The leaf water potential varied relatively little and did not influence gas exchange during the measurement period. Our results suggest that the same cause-effect relationships function at contrasting areas. However, leaves at the higher altitude had higher photosynthetic capacity, reflecting acclimation to higher light levels. Trees at both areas nevertheless achieved similar leaf assimilation rates since assimilation was down-regulated by stomatal closure due to the higher VPD at the higher altitude, while it became more light limited at the lower altitude. Gas exchange was thus limited by a high VPD or low light levels during the wet season, despite the ability of the species to acclimate to different conditions.
一个概念模型被用来解释环境和生理效应对落叶干燥热带林地树种乳香树（Boswellia papyrifera（Del.）Hochst.）叶片气体交换的影响。对于这个物种，我们旨在：（i）了解叶片气体交换的日变化模式，（ii）探索外部环境、内部生理和叶片气体交换之间的因果关系，（iii）探索环境变量对叶片气体交换的不同地点差异。在两个不同的地点（一个在高海拔，另一个在低海拔），对 90 棵树进行了连续几天的气体交换、潜在生理特征和环境变量的日变化测量。在早上，同化作用最高，然后在白天略有下降。相反，蒸腾作用从清晨到中午逐渐增加，主要是由于蒸汽压亏缺（VPD）的增加和逐渐关闭的气孔。叶片水势变化相对较小，在测量期间对气体交换没有影响。我们的结果表明，相同的因果关系在不同的地区起作用。然而，高海拔地区的叶子具有更高的光合能力，反映了对更高光照水平的适应。然而，由于高海拔地区 VPD 较高，气孔关闭导致同化作用下调，而在低海拔地区则更多地受到光限制，因此，尽管该物种有适应不同条件的能力，但在雨季，气体交换仍受到高 VPD 或低光照水平的限制。
