Effects of Salinity on Leaf δ13C in Three Dominant Mangrove Species along Salinity Gradients in an Estuarine Wetland, Southeast China

Many previous studies demonstrate that carbon stable isotope composition (usually expressed as isotopic ratio, δ13C) can reflect the integrated response of physiological processes to environment, but little is known of the variation in δ13C of mangrove plants as affected by salinity, especially in response to long term saline environment. The variation in δ13C of three dominant mangroves growing in long-term saline environments in the field was assessed. Mature leaves of Avicennia marina (Forsk) Vierh., Kandelia candel (L.) Duce., and Aegiceras corniculatum Blanco. were collected at seven sample sites covering seven salinity levels (14.07%–19.83%) at a natural mangrove wetland located in southeast China. The δ13C values varied from −31.46% to −27.33‰ with increasing salinity, reflecting the typical C3 pathway of CO2 fixation. The δ13C was positively related to salinity in K. candel and A. marina, and the reverse was observed in A. corniculatum, even though the correlations were not statistically significant for A. corniculatum and A. marina. The mean δ13C at high salinity was, in descending order, K. candel > A. marina > A. corniculatum. It is concluded that responses of δ13C to salinity is species-dependent and assessment of carbon isotopic composition is helpful for evaluating the salt tolerance of mangrove species, but it should be used with caution when comparing the salt tolerance between different species, particularly when they have the different patterns of δ13C in response to salinity.