抄録
Understanding the variations in the natural abundance of a nitrogen isotope ratio (δ15N) within a plant can help determine the reliability of using a plant parts’ δ15N as an indicator of δ 15N in the entire plant. However, little is known about patterns of δ 15N variation, even within major plant organs such as the leaves. The aim of the present study was to determine variations in δ 15N within the foliage, with emphasis on the positions and nitrogen concentration in the leaves. From two habitats (mud swamp and peat swamp), three leaves of the tropical evergreen tree Combretocarpus rotundatus were collected at each of nine positions (three leaf positions within a branch [apical to basal] three branch positions within a tree [high to low]), and the nitrogen concentration and δ 15N were examined. In the mud swamp site, leaf δ 15N varied according to the branch and leaf positions (the variation within the foliage reached 3‰) and higher δ15N values were obtained from apical leaves on higher branches. At both habitats, the δ15N variations positively correlated with the leaf nitrogen concentration. The present study indicated that the δ15N in foliage exhibited position-related large variations associated with the leaf nitrogen concentration. These findings suggested that when using leaf δ15N as a reliable indicator of the ecophysiological behaviour of plants, variations associated with leaf and branch positions must be taken into account, at least in the case of C. rotundatus growing in the tropics.
