Effects of Leaf Position and Leaf Order on Photosynthesis and Inorganic Carbon Utilization in Seagrass

Abstract:

To explore the effects of leaf position and leaf order on the photosynthesis and inorganic carbon utilization of tropical seagrasses, the light response curves, photosynthetic fluorescence, pH drift and HCO₃^– utilization of different parts of the leaves of Thalassia hemprichii and Cymodocea rotunda in the same habitat were studied. The results showed that the middle part of the seagrass leaves had a higher net photosynthetic rate (P_n), the base was higher than the top, and the young leaves were higher than the mature leaves; the maximum photosynthetic efficiency (F_v/F_m) of the leaf top was lower than that of other parts; the photosynthetic pigment content in the middle part of the leaves was higher than that in the top and base, and the photosynthetic pigment content in the young leaves was higher than that in the mature leaves. Both seagrass species could effectively utilize HCO₃^– in seawater as a carbon source, but the mature leaves had a better ability to utilize HCO₃^– than the young leaves, and the middle part of the leaves had a better ability to utilize HCO₃^– than the top and base. Therefore, although the two seagrass species have developed similar strategies for light energy and HCO₃^– utilization in the same habitat, their photosynthesis and inorganic carbon utilization capabilities vary with leaf position and leaf order.