Canopy Development and Leaf Nitrogen Distribution in a Stand of Carex Acutiformis

Seasonal changes in leaf nitrogen distribution were examined in the canopy of a Carex acutiformis stand in a wet meadow area. Although there was a tendency for leaf nitrogen concentration to decrease with increasing leaf age in any one layer of the canopy, nitrogen concentration increased significantly with plant height despite increasing age of leaf portions higher in the canopy. This suggests a predominant effect of the light climate on the nitrogen distribution within the canopy. During the growing period, standing crop dry mass increased significantly, while the increase in the standing crop of nitrogen was marginal. The amount of nitrogen decreased in the lower layers and increased in the upper layers, and a strongly decreasing gradient of nitrogen concentration developed from the top to the bottom of the canopy. It is suggested that this gradient resulted mainly from leaf tips with high nitrogen concentrations being lifted to higher positions because of growth at the base, with some retranslocation of nitrogen downwards from senescing tips to active parts. The distribution of nitrogen concentration became less uniform during the growing period, thus supporting the prediction that nitrogen concentration should become less uniformly distributed with development of the canopy.