Photosynthesis Related Characteristics of Upper and Lower Canopy Leaves of Kandelia obovata, a Mangrove Species in Taiwan

Abstract

To understand the light use properties of canopy leaves in K. obovata, the dominant mangrove species in the west coast of northern Taiwan, I compared photosynthesis related characters, such as leaf angles, leaf area, stomatal density, specific leaf area, and chlorophyll fluorescence, of upper and lower canopy leaves of the species. Leaves that had developed in exposed positions (upper canopy) exhibited significantly steeper leaf angles, smaller leaf area, higher stomatal density and lower specific leaf area than those in shaded positions (lower canopy). No significant difference was found in chlorophyll (Chl) content per unit leaf area and Chl a/b ratio between the two types of leaves. In contrast, compared to lower canopy leaves, upper canopy leaves had higher nitrogen content per unit leaf area indicating a higher light saturated CO2 assimilation. Chlorophyll fluorescence measurement revealed that photosaturated electron transport rate (ETR) and the photon flux required to saturate ETR were significantly higher in upper canopy leaves than in lower canopy leaves. The plasticity in morphological and physiological response to variation in light regimes may represent an important mechanism for K. obovata to adapt to the saline and nitrogen limiting environment.