Plasticity of leaf morphology of Bruguiera sexangula to salinity zones in Bangladesh’s Sundarbans

Bruguiera sexangula (Lour.) Poir is an exclusive evergreen mangrove species to the Sundarbans of Bangladesh. It grows well in moderate saline zones with full sunlight. This study presents leaf morphological plasticity in B. sexangula to saline zones. Leaves were sampled from different saline zones and various morphological traits were measured. The results exposed a wide deviations of leaf size parameters: leaf length varied 6.6–17.3 cm; width 2.7–7.8 cm; upper quarter width 2.2–6.5 cm; down quarter width 2.5–7.3 cm; and petiole length 0.17–1.43 cm. Leaf length was significantly larger in fresh water than in other salinity zones, whereas, leaf width, upper and lower leaf quarters were significantly larger in medium saline zone. Leaf shape parameters showed a large variation among saline zones. Leaf base angle was significantly larger in both medium and strong salinity zones. Tip angle was significantly greater in medium salinity zone. Leaf perimeter was significantly larger in fresh water but leaf area was significantly bigger in medium saline zone. Leaf index and specific leaf area were maximum in moderate saline zone. Plasticity index was the highest in moderate saline for almost all the parameters presented. The ordination (PCA) showed clusters of leaf samples although there were some overlap among them which suggested a salt-stress relationship among salinity zones. The results indicate that B. sexangula had a plasticity strategy on leaf morphological parameters to salinity in the Sundarbans. This study will provide basic information of leaf plasticity of this species among saline zones which will help for site selection of coastal planting and will also provide information for policy makers to take necessary steps for its conservation.