3. Results

Leaf structural traits varied significantly among the 10 sampled mangrove species (Table 2). The most variable traits were LV, LFM, LSM, and LDM, with a coefficient of variation (CV) approximately 60%. In contrast, LCC, LT, LDMC, LD, and LMA were the least variable, with CVs < 30%. LA and WSD were moderately variable (CV= 48.81% and 42.00%, respectively). The LCC, LA, LT, LV, LFM, LSM, LDM, and LMA increased significantly, and the WSD decreased from the low to high intertidal zones (Table 3 and Figure 1, p < 0.05). However, no significant differences between intertidal gradients were found for LDMC and LD. Compared with shrubs, trees had greater LA, LV, LFM, LSM, and LDM and lower LMA (Table 3 and Figure 1, p < 0.05), while growth form had no significant effect on the other traits. Additionally, we found significant interactive effects between growth forms and intertidal gradients on all traits, except for LMA. Trees in high intertidal zones had greater LCC, LA, LV, LFM, LSM, and LDM and lower LT than shrubs (Table 3 and Figure 1, p < 0.05), while differences in these traits between the growth types were not apparent in low intertidal zones. The LDMC, LD, and WSD were higher for shrubs than for trees only in low intertidal zones (Table 3 and Figure 1,p < 0.05), but these differences were not significant in high intertidal zones. The PCA results showed that Axis 1 and Axis 2 explained 48.9% and 23.2% of the total variance, respectively (Figure 2). Two independent dimensions of trait variation stood out within this plane. One dimension (upper left to lower right in Figure 2) ran from short and small DBH species with ‘conservative’ leaves (high LMA, LDMC, and LD) to tall and large DBH species with ‘acquisitive’ leaves (low LMA, LDMC, and LD). The other ran from large LA species tending to have thick and heavy leaves to small LA species tending to have thin and light leaves (lower left to upper right in Figure 2). Among all morphological and physiological characteristics, LMA, LDMC, LD, LCC, and WSD were negatively correlated with plant height and diameter (Figure 3). Similar patterns of LMA, LDMC, LD, LCC, and WSD in relation to plant height and diameter were found when intertidal zones and growth forms were analyzed individually, with LMA, LDMC, LD, LCC, and WSD decreasing with plant height and diameter (Appendix Figures S1 and S2). When regression slopes between different growth forms and intertidal gradients were tested, only LCC between high and low tides responded differently to plant diameter (p < 0.05, Appendix Table S2).