Abstract
To better understand the effects of light and salinity on the gas exchange and morphological features of mangrove trees, we examined seedlings of Avicennia alba Bl. and Bruguiera gymnorrhiza (L.) Lamk. Seedlings of the two species were cultivated at three light levels (100%, 50%, and 20% sunlight) and five salinity levels (0, 10, 20, 30, and 40 ppt). Changes in characteristics of gas exchange (maximum gross photosynthetic rate, stomatal conductance, transpiration rate, dark respiration rate, and water use efficiency) and leaf morphology (anatomy, specific leaf area, and leaf porosity) were recorded and analyzed. Gas exchange characteristics and leaf morphological features of A. alba were affected mainly by light environments and less by salinity levels, whereas those of B. gymnorrhiza were affected by both light environments and salinity levels. This can support a wider range of salt tolerance of A. alba. For A. alba, almost all gas exchange characteristics were lower at a salinity of 0 ppt (fresh water) compared to other salinity levels, whereas those of B. gymnorrhiza were not. The leaves of B. gymnorrhiza under high relative light intensity were thicker than under low relative light intensity due to increases in both palisade and spongy layer thickness. In contrast, A. alba leaves showed increased palisade layer thickness without changing leaf thickness under high relative light intensity.
