Brooks J Renée, Sprugel Douglas G, Hinckley Thomas M
College of Forest Resources, University of Washington, AR-10, 98195, Seattle, WA, USA.
Oecologia. 1996 Mar;107(1):21-32. doi: 10.1007/BF00582231.
Variation in the photosynthetic function ofAbies amabilis foliage within a canopy was examined and related to three different processes that affect foliage function: foliage aging, sun-shade acclimation that occurred while foliage was expanding, and reacclimation after expansion was complete. Foliage produced in the sun had higher photosynthesis at light saturation (A , μmol·m·s), dark respiration (μmol·m·s), nitrogen content (g·m), chlorophyll content (g·m), and chlorophylla:b ratio, and a lower chlorophyll to nitrogen ratio (chl:N), than foliage produced in the shade. As sun foliage becomes shaded, it becomes physiologically similar to shade foliage, even though it still retains a sun morphology. Shaded sun foliage exhibited lowerA , dark respiration, nitrogen content, and chlorophylla:b ratio, and a higher chl:N ratio than sun foliage of the same age remaining in the open. However, shaded sun foliage had a higher chlorophyll content than sun foliage remaining in the open, even though true shade foliage had a lower chlorophyll content than sun foliage. This anomaly arises because as sun foliage becomes shaded, it retains a higher nitrogen content than shade foliage in a similar light environment, but the two forms have similar chl:N ratios. Within the canopy, most physiological indicators were more strongly correlated with the current light environment than with foliage age or leaf thickness, with the exception of chlorophyll content.A decreased significantly with both decreasing current light environment of the foliage and increasing foliage age. The same trend with current light and age was found for the chlorophylla:b ratio. Foliage nitrogen content also decreased with a decrease in current light environment, but no distinct pattern was found with foliage age. Leaf thickness was also important for predicting leaf nitrogen content: thicker leaves had more nitrogen than thinner leaves regardless of light environment or age. The chl:N ratio had a strong negative correlation with the current light environment, and, as with nitrogen content, no distinct pattern was found with foliage age. Chlorophyll content of the foliage was not well correlated with any of the three predictor variables: current light environment, foliage age or leaf thickness. On the other hand, chlorophyll content was positively correlated with the amount of nitrogen in a leaf, and once nitrogen was considered, the current light environment was also highly significant in explaining the variation in chlorophyll content. It has been suggested that the redistribution of nitrogen both within and between leaves is a mechanism for photosynthetic acclimation to the current light environment. Within theseA. amabilis canopies, both leaf nitrogen and the chl:N ratio were strongly correlated with the current light environment, but only weakly with leaf age, supporting the idea that changing light is the driving force for the redistribution of nitrogen both within and between leaves. Thus, our results support previous theories on nitrogen distribution and partitioning. However,A was significantly affected by both foliage age and the current light environment, indicating that changes in light alone are not enough to explain changes inA with time.
研究了花旗松冠层内叶的光合功能变化，并将其与影响叶功能的三个不同过程相关联：叶衰老、叶扩展时发生的阳生-阴生适应，以及扩展完成后的再适应。与阴生叶相比，阳生叶在光饱和时具有更高的光合速率（A，μmol·m⁻²·s⁻¹）、暗呼吸速率（μmol·m⁻²·s⁻¹）、氮含量（g·m⁻²）、叶绿素含量（g·m⁻²）和叶绿素a:b比值，以及更低的叶绿素与氮比值（chl:N）。当阳生叶被遮荫时，即使它仍保留阳生形态，其生理状态也变得与阴生叶相似。与仍处于开阔环境中的同龄阳生叶相比，被遮荫的阳生叶表现出较低的光合速率、暗呼吸速率、氮含量和叶绿素a:b比值，以及更高的chl:N比值。然而，被遮荫的阳生叶比仍处于开阔环境中的阳生叶具有更高的叶绿素含量，尽管真正的阴生叶叶绿素含量低于阳生叶。这种异常现象的出现是因为当阳生叶被遮荫时，在相似的光照环境下，它比阴生叶保留了更高的氮含量，但两种叶型具有相似的chl:N比值。在冠层内，除叶绿素含量外，大多数生理指标与当前光照环境的相关性比与叶龄或叶厚度的相关性更强。随着叶当前光照环境的降低和叶龄的增加，光合速率显著下降。叶绿素a:b比值也呈现出与当前光照和叶龄相同的趋势。叶氮含量也随着当前光照环境的降低而降低，但未发现与叶龄有明显的规律。叶厚度对于预测叶氮含量也很重要：无论光照环境或叶龄如何，较厚的叶比较薄的叶含有更多的氮。chl:N比值与当前光照环境呈强烈负相关，并且与氮含量一样，未发现与叶龄有明显规律。叶的叶绿素含量与三个预测变量（当前光照环境、叶龄或叶厚度）中的任何一个都没有很好的相关性。另一方面，叶绿素含量与叶中的氮含量呈正相关，并且一旦考虑氮含量，当前光照环境在解释叶绿素含量变化方面也非常显著。有人提出，叶内和叶间氮的重新分配是光合适应当前光照环境的一种机制。在这些花旗松冠层内，叶氮和chl:N比值都与当前光照环境密切相关，但与叶龄的相关性较弱，这支持了光照变化是叶内和叶间氮重新分配驱动力的观点。因此，我们的结果支持了先前关于氮分布和分配的理论。然而，光合速率受到叶龄和当前光照环境的显著影响，这表明仅光照变化不足以解释光合速率随时间的变化。
