Development Of Propagules Of Nonviviparous Mangroves And Intertidal Distribution

Vivipary is so strongly associated with mangroves that it is suggested to have adaptive significance in the intertidal saline environment.But the existence of nonviviparous mangroves makes it suspicious.Developmental process of propagules of five species from nonviviparous mangroves Sonneratia was studied,which was compared with viviparous mangroves as well.At the same time,the relation between propagule traits and distribution of Sonneratia in intertidal zone was discussed.The results indicated:1.There was commonness in propagules development between Sonneratia and viviparous mangroves.(1) High water content was both maintained throughout development in viviparous mangroves and Sonneratia.(2) Density of mature fruits was close to or lower than seawater,thus the propagules can float.(3) The dynamics of the elements on a dry weight basis in the fruits indicated a desalinating process.Moreover,the content of C1,Na,Ca or Mg was lower in fruits than those in the mature leaves and calyx.Elements concentrations also show the trend of decreasing.(4) The contribution of inorganic osmotica in mature propagules was less than true vivipary,but was more than cryptovivipary.Conclusion:Comparing these results with others' research about viviparous mangroves, distinct differences were not found.The hypothesis that vivipary among mangroves is an adaptation to salinity was not well supported.The value of vivipary should be reconsidered.2.Numerous factors influence distribution pattern of mangroves.There was close connection between propagule traits and distribution of Sonneratia.(1) The rank order of density of mature fruits was:S.alba＞S.caseolaris,S.× gulngai＞S.×hainanensis＞S.ovata.(2) The rank order of Na/K ratio of mature fruits was:S.alba＞S.×gulngai,S.×hainanensis＞S.ovata＞S.caseolaris.The rank order of Na/K ratio of mature leaves was:S.alba＞S.xhainanensis,S.ovata＞S.×gulngai,S. caseolaris.Conclusion:Mangrove distribution in intertidal zone may be related to density of propagules.Species whose adults are found on the landward edge of the intertidal zone,have propagules of small density;species whose adults are found on the seaward edge of the swamp,have propagules of large density.In the estuary which is affected by fresh water,distribution of mangrove species along estuaries has been shown to be related to salinity tolerance.Proliferate of mangrvoes includes stage of propagules dispersal and colonization.A hypothesis is proposed that density is key factor which impacts the distribution of mangroves in the stage of propagules dispersal.In the stage of colonization,the ability of salt tolerance of mangroves is one of important factors which decide whether propagules survive or not and eventually affect the distribution of mangrvoes to some extent.