Variation in the δ13C of Two Mangrove Plants is Correlated with Stomatal Response to Salinity

To better understand the relationship between salinity and the carbon stable isotope composition (expressed as δ13C) of mangrove plants and to test whether the patterns of variation in δ13C of mangrove plants differ from those of nonhalophytes as response to salinity, the effect of salinity on leaf δ13C in two dominant mangrove species, Aegiceras corniculatum and Kandelia candel, was studied. Furthermore, to determine whether the variation in δ13C of mangrove species is adjusted by stomatal conductance, K. candel was selected as an example, and leaf gas-exchange characteristics of the seedlings were measured. It was observed that both mangrove species had a lower leaf δ13C under their optimum salinity (1.50% for Ae. corniculatum and 2.00% for K. candel). This variation in δ13C of mangrove plants was attributable largely to stomatal adjustment as for nonhalophytes in which a strong correlation between δ13C and relevant photosynthetic properties is observed. This result suggests that the different response pattern in δ13C was a consequence of the variation in stomata in relation to the different tolerance to salinity. The optimum salinity inferred by leaf δ13C provides a feasible method for comparing salt tolerance between mangrove plants belonging to different species, which is useful for mangrove restoration.