Development of Viviparous and Nonviviparous Mangrove Propagules

Vivipary is common in several mangrove species and is generally considered an adaptation to the intertidal saline environment. However, the coexistence of many nonviviparous mangroves makes this view controversial. This study investigated the propagule development of two nonviviparous mangrove species, Sonneratia alba and S. caseolaris, with marked differences in salt tolerance and distribution. The changes in the density, water content, and concentrations of the five main osmoregulatory elements (Cl, Na, K, Ca, and Mg) were determined. As the propagules of S. alba and S. caseolaris mature, the element concentrations (mg/g) in the propagules gradually decreased, indicating a desalinating process. Moreover, the Cl, Na, Ca, and Mg content in the propagules was lower than in the mature leaves and calyx. Similar to the development of vivipary mangroves, the development of the propagules of nonviviparous mangroves is also a desalinating process. Compared with the propagule development of viviparious mangrove species, our results indicate that vivipary may not be a distinct adaptation of mangrove species to saltwater habitats.