Nilsen Erik Tallak
Department of Biology, Virginia Polytechnic Institute and State University, 24061, Blacksburg, Virginia, USA.
Oecologia. 1985 Jan;65(2):296-302. doi: 10.1007/BF00379233.
Leaf orientation (azimuth and angle) and leaf curling were measured seasonally and diurnally on Rhododendron maximum L. under an evergreen and a deciduous canopy. The microclimatic conditions under the evergreen canopy (mixed pine and hemlock) were characterized by lower irradiance but similar temperature, and vapor pressure deficit (vpd) to that under the deciduous canopy (mixed oak and maple). Under both canopies irradiance was more intense during winter months.On a seasonal basis leaf angle was closer to horizontal under the evergreen canopy but there was no difference between leaf curling in the two sites. Stomatal conductance was higher under the deciduous canopy but stomata were closed in the winter (following canopy abscission) under the evergreen and deciduous canopies even during warm winter days. Leaf water potentials were lower in the winter and Rhododendron maximum had higher leaf water potentials under the evergreen canopy.Significant association between mean leaf angle and curling index were found above a mean leaf angle of 70°. Leaf curling was highly associated with leaf temperature where 0° C was a critical value stimulating leaf curling. Leaf angle was linearly related to leaf temperatures above 0° C although this relationship was different under the two canopy types as a result of differing irradiance or differing water potential.
在常绿和落叶树冠下，对大花杜鹃（Rhododendron maximum L.）的叶片方向（方位角和角度）及叶片卷曲情况进行了季节性和昼夜测量。常绿树冠（松树和铁杉混交林）下的微气候条件特点是光照较低，但温度和水汽压亏缺（vpd）与落叶树冠（橡树和枫树混交林）下相似。在两个树冠下，冬季月份的光照都更强。从季节来看，常绿树冠下叶片角度更接近水平，但两个地点的叶片卷曲情况没有差异。落叶树冠下气孔导度更高，但即使在温暖的冬日，常绿和落叶树冠下的气孔在冬季（树冠落叶后）都会关闭。冬季叶片水势较低，且大花杜鹃在常绿树冠下具有更高的叶片水势。在平均叶片角度高于70°时，发现平均叶片角度与卷曲指数之间存在显著关联。叶片卷曲与叶片温度高度相关，0°C是刺激叶片卷曲的临界值。叶片角度与0°C以上的叶片温度呈线性关系，不过由于光照或水势不同，这种关系在两种树冠类型下有所不同。
