Muth Christine C, Bazzaz F
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, 02138, USA.
Oecologia. 2002 Jul;132(2):197-204. doi: 10.1007/s00442-002-0957-x. Epub 2002 Jul 1.
Light with decreased red:far-red (R:FR) ratios may signal neighbor presence and trigger plant developmental responses. There is some evidence that plant canopies forage towards increased R:FR ratios, but it is unclear to what extent R:FR versus the total amount of photosynthetically active radiation (PAR) influences canopy foraging responses among forest trees. The objective of this study was to examine the relative importance of PAR and R:FR as photosensory cues leading to tree canopy foraging responses. Seedlings of Betula papyrifera Marshall (paper birch) were grown in an experimental garden. Each seedling was germinated and grown in its own shading structure and exposed to two spatially separated light environments, in a factorial design of PAR and R:FR. Plant canopy foraging was evaluated at the end of one growing season in terms of canopy displacement, canopy area, leaf number, direction of stem lean, petiole aspect, and lamina aspect with respect to experimental light treatments. Leaf number and canopy area were greater on the high PAR sides of plants, irrespective of the R:FR treatment. Seedling canopies were displaced towards the direction of high PAR, but this relationship was not significant across all treatments. Petiole aspect was random and showed no significant directedness towards any of the light treatments. Lamina aspect and the direction of stem lean were distributed towards the direction of high PAR, irrespective of the R:FR treatment. Overall, first-year B. papyrifera seedlings used PAR, rather than R:FR ratio, as a photosensory cue for canopy light foraging.
红光与远红光比例降低的光可能表明有邻体存在，并触发植物的发育反应。有证据表明，植物冠层会朝着增加的红光与远红光比例方向生长，但尚不清楚红光与远红光比例相对于光合有效辐射（PAR）总量对林木冠层生长反应的影响程度。本研究的目的是检验光合有效辐射和红光与远红光比例作为导致树冠生长反应的光感线索的相对重要性。白桦（Betula papyrifera Marshall）幼苗在实验花园中生长。每株幼苗在其各自的遮光结构中萌发和生长，并暴露于两个空间分离的光照环境中，采用光合有效辐射和红光与远红光比例的析因设计。在一个生长季结束时，根据冠层位移、冠层面积、叶片数量、茎倾斜方向、叶柄朝向和叶片朝向等方面，对植物冠层生长进行了评估，这些评估均针对实验光照处理。无论红光与远红光比例处理如何，植物光合有效辐射较高一侧的叶片数量和冠层面积都更大。幼苗冠层向光合有效辐射高的方向移动，但这种关系在所有处理中并不显著。叶柄朝向是随机的，对任何光照处理均未表现出显著的方向性。无论红光与远红光比例处理如何，叶片朝向和茎倾斜方向都朝着光合有效辐射高的方向分布。总体而言，一年生白桦幼苗利用光合有效辐射而非红光与远红光比例作为冠层光照生长的光感线索。
