Pons Thijs L, van Rijnberk Hans, Scheurwater Ingeborg, van der Werf Adrie
Dept. Plant Ecology and Evolutionary Biology, University Utrecht, P.O. Box 800.84, 3508 TB, Utrecht, The Netherlands.
Dept. Evolutionary Biology, University Leiden, Schelpenkade 14a, 2313 ZT, Leiden, The Netherlands.
Oecologia. 1993 Sep;95(3):416-424. doi: 10.1007/BF00320997.
Carex acutiformis and Brachypodium pinnatum were grown with a uniform distribution of photosynthetic photon flux density (PFD) with height, and in a vertical PFD gradient similar to the PFD gradient in a leaf canopy. Distribution of organic leaf N and light-saturated rates of photosynthesis were determined. These parameters were also determined on plants growing in a natural vegetation stand. The effect of a PFD gradient was compared with the effect of a leaf canopy. In Brachypodium, plants growing in a vegetation stand had increasing leaf N with plant height. However, distribution of leaf N was not influenced by the PFD gradient treatment. The gradient of leaf N in plants growing in a leaf canopy was not due to differences within the long, mostly erect, leaves but to differences between leaves. In Carex, however, the PFD gradient caused a clear increase of leaf N with height in individual leaves and thus also in plants. The leaf N gradient was similar to that of plants growing in a leaf canopy. Leaf N distribution was not affected by nutrient availability in Carex. In most cases, photosynthesis was positively related to leaf N. Hence, lightsaturated rates of photosynthesis increased towards the top of the plants growing in leaf canopies in both species and, in Carex, also in the PFD gradient, thus contributing to increased N use efficiency for photosynthesis of the whole plant. It is concluded that in Carex the PFD gradient is the main environmental signal for leaf N allocation in response to shading in a leaf canopy, but one or more other signals must be involved in Brachypodium.
尖锐苔草和羽裂短柄草在光合光子通量密度（PFD）随高度呈均匀分布的条件下生长，且处于与叶冠层中PFD梯度相似的垂直PFD梯度环境中。测定了叶片有机氮分布和光合光饱和速率。这些参数也在自然植被群落中生长的植物上进行了测定。将PFD梯度的影响与叶冠层的影响进行了比较。在羽裂短柄草中，生长在植被群落中的植株叶片氮含量随株高增加。然而，叶片氮的分布不受PFD梯度处理的影响。生长在叶冠层中的植株叶片氮梯度并非源于大多细长且直立的叶片内部差异，而是叶片之间的差异。然而，在尖锐苔草中，PFD梯度导致单叶叶片氮含量随高度明显增加，进而植株整体叶片氮含量也增加。叶片氮梯度与生长在叶冠层中的植株相似。尖锐苔草中叶片氮分布不受养分有效性的影响。在大多数情况下，光合作用与叶片氮呈正相关。因此，在两种植物中，生长在叶冠层中的植株光合光饱和速率均朝着植株顶部增加，在尖锐苔草中，在PFD梯度环境下也是如此，从而有助于提高整株植物光合作用的氮利用效率。得出的结论是，在尖锐苔草中，PFD梯度是叶片氮分配以响应叶冠层遮荫的主要环境信号，但在羽裂短柄草中一定涉及一个或多个其他信号。
