Sensitivity to chilling temperatures and distribution differ in the mangrove species Kandelia candel and Avicennia marina

We compared the effects of short-term (hours) and long-term (days) exposure to chilling temperatures on the photosynthetic gas exchange, leaf characteristics and chlorophyll a fluorescence of seedlings of the mangrove species Kandelia candel Druce and Avicennia marina (Forsk.) Vierh. Both species occur along the west coast of Taiwan, but K. candel occurs further north than A. marina. We hypothesized that temperature was one of the major environmental factors limiting the northern distribution of A. marina. Avicennia marina was more sensitive to chilling temperatures than K. candel. Leaves of both species showed reductions in light-saturated photosynthetic rates (Amax), stomatal conductance (gs) and quantum yield of photosystem II after a 1-h exposure to 15 degrees C, with A. marina showing significantly greater reductions in Amax and gs than K. candel. No significant differences in Amax, gs and electron transport rate (ETR) were found between leaves of K. candel grown at 15 and 30 degrees C for 10 days. However, leaves of A. marina grown for 10 days at 15 degrees C had significantly lower Amax, gs and ETR than plants grown at 30 degrees C. After 20 days at 15 degrees C, leaf mass per area of both species was increased significantly, whereas area-based chlorophyll concentrations were reduced, with significantly greater changes in A. marina than in K. candel. We concluded that sensitivity to low winter temperatures is a primary limiting factor in the distribution of A. marina along the western coast of Taiwan.