Importance of the gradient in photosynthetically active radiation in a vegetation stand for leaf nitrogen allocation in two monocotyledons.
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.
Dept. Plant Ecology and Evolutionary Biology, University Utrecht, P.O. Box 800.84, 3508 TB, Utrecht, The Netherlands.
Thijs L
TL
Pons
Dept. Evolutionary Biology, University Leiden, Schelpenkade 14a, 2313 ZT, Leiden, The Netherlands.
Hans
H
van Rijnberk
Dept. Plant Ecology and Evolutionary Biology, University Utrecht, P.O. Box 800.84, 3508 TB, Utrecht, The Netherlands.
Ingeborg
I
Scheurwater
Centre for Agrobiological Research, P.O. Box 14, 6700 AA, Wageningen, The Netherlands.
Adrie
A
van der Werf
Brachypodium pinnatum; Carex acutiformis; Nitrogen allocation; Photosynthesis