落叶阔叶林内的光合作用和气孔传导率特征(英文)

本文根据Wang和BMdocchi(1989)最近提出的冠层辐射模型,进一步给出了一个模拟冠层光合作用速率和气孔传导率的模式.模式将冠层中每一层的叶面积分为向光叶、半影叶、和全遮荫叶三种,并分别计算其光合作用速率和气孔传导率。计算得到的光合速率廓线表明,在落叶阔叶林内,冠层下部的叶片常处于光照不足状态;半影效应使得透过林冠达于底部的辐射量增大,这对于林下植物的光合作用是有利的。 模式计算值与实测值之间的微弱差别应归因于纯辐射模型无法考虑湍流输送机制造成的CO_2传输和冠层底部耐荫性叶对于低光照的适应能力。

Characteristics of Photosynthesis and Stomatal Conductance Within a Deciduous Forest

Based on our numerical radiation model (Wang and Baldocchi, 1989), we have presented a model that can simulate the photosynthetic process within a deciduous forest canopy. The model divides the whole leaf area of the canopy into sunlit, penumbral and umbral leaf area with each having different photosynthetic characteristics and different stomatal conductance. In general, the sunlit leaf area has higher photosynthetic rates than the penumbral and umbral leaf area. The leaf photosynthetic rate profiles show that in the typical Oak-hickory forest, the understory, whose leaves are always shaded, is deficient in light and its assimilation rate is negative. The penumbra phenomena lets more radiation penetrate to the lower part of the canopy, which is an important compensation to the light deficiency for under vegetation. Comparing with the exponential-like curves from non-penumbra model, the maximum value of photosynthesis in the upper crown is properly mimicked. The different diurnal courses at different heights of the canopy show that middle-upper part of the canopy is the place where the physiological processes occur most actively. Only here the diurnal courses of photosynthesis and stomatal conductance have two peaks, which means that photosynthetic rate reaches its maximum values in middle of morning or middle of afternoon when the sun is slant on the canopy rather than at noon when the sun is highest. Besides some ecological reasons, the canopy architectural structure that gives a minimum difference between leaf angle and solar angle is also an important factor.