Hokkaido Research Center, Forestry and Forest Products Research Institute, Sapporo, 062-8516, Japan.
Department of Plant Ecology, Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba, 305-8687, Japan.
Sci Rep. 2018 Jan 11;8(1):503. doi: 10.1038/s41598-017-18766-0.
As photoinhibition primarily reduces the photosynthetic light use efficiency at low light, sunfleck-induced photoinhibition might result in a fatal loss of carbon gain in the shade leaves within a canopy with barely positive carbon balance. We hypothesized that shade leaves at the lower canopy might retain a certain amount of leaf nitrogen (N) to maintain energy consumption via electron transport, which contributes to circumventing photoinhibition during sunflecks to keep efficient utilization of low light during the rest period of daytime. We investigated excess energy production, a potential measure of susceptibility to photoinhibition, as a function of N distribution within a Japanese oak canopy. Optimal N distribution, which maximizes canopy carbon gain, may lead to a higher risk of photoinhibition in shade leaves during sunflecks. Conversely, uniform N distribution would cause a higher risk of photoinhibition in sun leaves under the direct sunlight. Actual N distribution equalized the risk of photoinhibition throughout the canopy indicated by the constant excess energy production at the highest light intensities that the leaves received. Such a homeostatic adjustment as a whole canopy concerning photoinhibition would be a key factor to explain why actual N distribution does not maximize canopy carbon gain.
由于光抑制主要降低低光下的光合作用光利用效率，光斑诱导的光抑制可能会导致冠层内几乎没有正碳平衡的荫蔽叶片中碳增益的致命损失。我们假设较低冠层的荫蔽叶片可能会保留一定量的叶片氮（N），以通过电子传递维持能量消耗，这有助于在光斑期间规避光抑制，以在白天的休息时间有效利用低光。我们研究了过量能量产生，这是衡量对光抑制敏感性的一个潜在指标，作为日本栎树冠层内 N 分布的函数。最佳的 N 分布可以最大化冠层的碳增益，但可能会增加光斑期间荫蔽叶片发生光抑制的风险。相反，均匀的 N 分布会导致在直射阳光下的阳生叶片发生光抑制的风险更高。实际的 N 分布通过叶片接收的最高光强下的恒定过量能量产生使整个冠层的光抑制风险均等化。这种整体冠层关于光抑制的自衡调整可能是解释为什么实际的 N 分布不会使冠层的碳增益最大化的关键因素。
