Pfitsch William A, Pearcy Robert W
Department of Botany, University of California, 95616, Davis, CA, USA.
Oecologia. 1989 Sep;80(4):465-470. doi: 10.1007/BF00380067.
The relationships between carbon gain and availability of sunfleck- and diffuse-light were determined for Adenocaulon bicolor by following the daily courses of assimilation and incident PFD on different days and locations in a redwood forest understory. Total PFD for the days sampled ranged from 1 to 4% of full sun values. Sunflecks accounted for 50 to 90% of the total PFD and were responsible for the majority of variation among days and locations. Each day had several clusters of sunfleck activity separated by relatively long intervals of diffuse light. Most sunflecks had maximum PFDs below the photosynthetic light-saturation point, and they had a median length and diffuse light interval separating them of 2 s. Daily carbon gain varied from 14 to 40 mmol md and was more strongly correlated with differences among days in total sunfleck PFD (r =0.81) than with variation in diffuse PFD (r =0.54). The assimilation that was attributable to sunflecks ranged from essentially zero on one day to 30 to 65% of the total on the other days. Carbon gain on most days was 70 to 80% of that predicted by a model based on the measured light dependences of assimilation. This model assumed an instantaneous response to changes in PFD, whereas incomplete photosynthetic induction probably limited the capacity to respond to sunflecks and therefore limited carbon gain on most days.
通过追踪红杉林下不同日期和地点的同化作用和入射光合有效辐射（PFD）的日变化过程，确定了双色腺梗菜碳获取与光斑光和漫射光可利用性之间的关系。采样日的总PFD范围为全日照值的1%至4%。光斑占总PFD的50%至90%，是不同日期和地点之间大部分变化的原因。每天都有几簇光斑活动，其间被相对较长的漫射光间隔隔开。大多数光斑的最大PFD低于光合光饱和点，它们的中位长度和将它们隔开的漫射光间隔为2秒。日碳获取量在14至40 mmol m²d之间变化，与总光斑PFD的日差异（r = 0.81）的相关性比与漫射PFD的变化（r = 0.54）更强。归因于光斑的同化作用范围从某一天的基本零到其他日子的占总量的30%至65%。大多数日子的碳获取量是基于测量的同化作用光依赖性的模型预测值的70%至80%。该模型假设对PFD变化有瞬时响应，而不完全的光合诱导可能限制了对光斑的响应能力，因此限制了大多数日子的碳获取量。
