Vegetative And Reproductive Characteristics Of Viviparous Mangroves

Mangroves are the most important primary producers in tropical and subtropical gulf estuary. Under the long-term mutual selection with environment, mangroves gradually formed the specific vegetative and reproductive adaptations. Mangroves are classified into two groups:true mangroves and mangrove associates. True mangroves possess complete fidelity to the mangrove environment; that is, they occur only in mudflat and do not extend into terrestrial communities. Bruguiera, Kandelia, Rhizophora and Ceriops are the typical true mangroves which collectively form a natural tribe, Rhizophoreae, within the family. Two of the most outstanding characteristics of Rhizophoreae mangroves are stipules which is consistent with the number of new leaves, and vivipary of the embryo. The number of fallen stipules and leaves could availably evidence the growth and renewal of mangroves. The study of viviparous reproduction is a significant approach to uncover the mangroves life history strategies, community succession, biological evolution, etc.During April2009to November2011in Dongzhaigang Bay, Hainan, a study was conducted on the litterfall of Bruguiera sexangula, Kandelia obovata, Rhizophora stylosa and Ceriops tagal. The primary objective was to study the vegetative and reproductive characteristics of viviparous mangroves and provide theoretical guides for preservation and restoration of mangrove ecosystems. Main conclusions are as follow:1. There were significant differences in litterfall production among the4mangrove communities. The descending order was:Rhizophora stylosa community (1406.60±64.60g m-2a-1)>Bruguiera sexangula community (1198.94±73.04g m-2a-1)> Kandelia obovata community (897.85±32.02g m-2a-1)> Ceriops tagal community (604.84±17.85g m-2a-1). The litterfall production of mangrove communities was higher than the terrestrial communities in the same latitude.2. Leaf was the dominant component in the litterfall of4mangroves. The monthly variation of litterfall production was roughly same with leaf. The drop time of reproductive organs was more concentrated, especially the hypocotyls which held an obvious peak for about2-3months. The maximum period of litterfall production coincided with the falling peak time of reproductive organs (mainly hypocotyls). 3. Among various climatic factors, the monthly mean temperature and precipitation have significant impacts on viviparous mangroves.4. Through the statistical analysis of leaves and stipules in litterfall, the growth status of4mangrove communities were introduced. Rhizophora stylosa community was gradually degrading, the number of whose fallen leaves was more than newborn leaves. While Kandelia obovata community and Ceriops tagal community were thriving with more newborn leaves. Bruguiera sexangula community was at the stable mature stage, which kept a good balance between the number of fallen leaf and newborn leaf.5. Germination and fall of leaves have occurred throughout the year in the same pattern with slight differences in time. Leaf falling of Bruguiera sexangula community and Kandelia obovata community were almost simultaneous with leaf germination. The leaf of Rhizophora stylosa community germinated a month earlier than fell. On the contrary, the leaf of Ceriops tagal community germinated2months later than fell.6. The reproductive developmental ratios of viviparous mangroves were generally lower than non-viviparous mangroves. The major restrictions on low developmental ratios were Stage II (flowers and fruitsâ†'small hypocotyls) and Stageâ…£ (middle hypocotylsâ†'mature hypocotyls). This phenomenon was associated with optimal resource allocation.7. According to the share of reproduction in litterfall, the reproductive investments of different mangroves can be drawn. The reproductive investments of different reproductive modes were significant different. Cryptoviviparous mangroves invested fewer resources to reproduction (1.6-33.7%). Non-viviparous mangroves, by comparison, contributed more resources to reproduction (17.3-41.1%). The reproductive investment of viviparous mangroves (7.6-37.6%) intervened between cryptoviviparous mangroves and non-viviparous mangroves. In the4typical viviparous mangroves, Rhizophora stylosa was more inclined to K-strategistis, who assigned less energy to reproduction and more energy to survival and competition. While, more energy of Bruguiera sexangula and Kandelia obovata was allocated into reproduction. They were inclined to r-strategistis. Ceriops tagal existed in r-K continuum. 8. Based on the analysis of flowering phenology of4mangroves, we found that Bruguiera sexangula was inclined to be continual flowering plant which held a relatively longer flowering duration and a shorter intermittent phase; Kandelia obovata, Rhizophora stylosa and Ceriops tagal were inclined to be annual flowering plant which held an obvious and short flowering period.9. There exists a significant relationship between natural arctogaean realms of4mangroves and their maturing sequence in China. As the latitude of natural arctogaean realm increased, the peak period of hypocotyls maturing occurs earlier. This is the result of mangroves interacting with environmental factors under the long-term mutual selection. More time would be provided for an earlier-matured hypocotyl to develop into a plantlet which can be able to stand the low temperature in next winter.