Significant niche overlap between native and exotic Sonneratia mangrove species along a continuum of varying inundation periods

Sonneratia apetala Buch.-Ham., an introduced mangrove species from Bangladesh, has been popularly used in mangrove afforestation in China for more than 20 years. Whether there is an overlap in niche between this exotic species and native mangrove species is still unknown. The purpose of this study is to evaluate differences in growth and physiological responses to tidal inundation between the exotic S. apetala and its congeneric species in China, Sonneratia caseolaris. A set of tidal tanks was used to simulate different tidal ranges by controlling different inundation periods (0, 2, 4, 6, 8, 10, 12 h). Both the inundation period and species showed significant effects on almost all morphological, growth and physiological parameters measured; however, there were no significant differences between the two species in the responses of these parameters to the inundation period, except for specific leaf area (SLA) and light compensation point (LCP). Significant increases in SLA under the long inundation periods (10, 12 h) for the exotic, but not for the native species, indicate that the exotic one tended to increase its leaf area for assimilation. Thus, the exotic S. apetala seedling exhibited phenotypic plasticity to tidal inundation similar that of the native, S. caseolaris, which suggests that the exotic and native Sonneratia species will occupy a similar niche along the entire tidal range.