Leaf morphological and anatomical plasticity in Sundri (Heritiera fomes Buch.-Ham.) along different canopy light and salinity zones in the Sundarbans mangrove forest, Bangladesh

摘要

Sundri ( Heritiera fomes Buch.-Ham.) is an evergreen mangrove tree species found abundantly in the freshwater zone of Sundarbans, Bangladesh and scattered in moderate or strong saline zones of the forest. H. fomes grows well in top canopy having full sunlight and even in full shade under the canopy. This study presents the plasticity of leaf morphological and anatomical characteristics in H. fomes due to variation of light intensity at different canopy depths and of salinity in different saline zones of Sundarbans. This study was conducted in two steps, firstly the light intensity and leaf phenotypic variations at different canopy depths (one-meter interval) in the fresh water zone of Sundarbans, secondly the leaf phenotypic variations in three saline zones having variable light environment at different canopy positions (top, middle and bottom) in each zone. Leaf samples were collected from three different salinity zones and each canopy positions and various morphological and anatomical characteristics were quantified. A wide range of variations were observed in the leaf parameters measured among the salinity zones of the Sundarbans and the canopy positions. The canopy of H. fomes showed an exponentially decreasing light gradient. Leaf plasticity index (PI) of all the parameters was developed for the salinity zones and the canopy positions of the Sundarbans. The ordination plots (PCA) suggested clear morphological and anatomical shift of the samples collected from different saline zones and canopy positions showing relationship to light and salt stresses in natural environment. Our results provide clear evidence on plastic strategy of H. fomes against salinity and light gradients in the Sundarbans.