Effects of elevational gradient on leaf and stomatal morphology of Caucasian alder (Alnus subcordata) in the Hyrcanian forest, Iran

Abstract

Alnus subcordata C.A.Mey (Betulaceae) is a commercial, fast growing species that is widely distributed in the Hyrcanian forest of northern Iran. In this study, the effect of altitude on the whole leaf and stomatal morphology of this species was analyzed. In eastern Mazandaran province, ten sites were selected along an elevational gradient. The altitudinal separation between sites was 100 m. At each site, leaves from six individual trees were collected for determination of leaf traits. Correlation analyses showed a significant, positive relationship of tooth number with altitude, whereas leaf blade and petiole length were significantly but inversely related to this factor. Similarly, stomatal length decreased with the increasing altitude. A principal component analysis (PCA) was performed to identify those traits causing the main differentiation between sites. Leaf width and length, together with petiole length, were best correlated with PC1 scores, whereas stomatal traits were best correlated with PC2 scores. The large plasticity of the studied leaf traits of A. subcordata was confirmed through a plasticity analysis (Pl = 0.56). The trait displaying the lowest plasticity was leaf base shape (Pl = 0.2). A high plasticity in leaf traits subjected to environmental fluctuations was also observed, especially for apex length, leaf length, petiole length, tooth number and size of stomata. These findings may explain the broad elevational distribution of A. subcordata in the Hyrcanian forest. It is concluded that leaf base shape is a valuable trait for
the taxonomy in the genus Alnus.