福建漳江口红树林区秋茄幼苗生长动态

通过福建漳江口红树林自然保护区内8个样方24个小样方人工种植600个秋茄胚轴，在3a时间内对秋茄胚轴建立、幼苗生长以及环境因子进行定期观测。研究结果表明：林缘空地的秋茄生长状况良好，白骨壤林内最不利于秋茄幼苗的生长。潮位、盐度、底质土壤理化因子不是造成该样地各样方间秋茄幼苗生长差异的主要原因。动物取食、光照状况以及种间竞争是限制秋茄生长的主要环境因子。秋茄胚轴在长根前易于随潮水漂走，底质土壤中自骨壤致密的根系抑制了秋茄胚轴的定植，导致白骨壤林内秋茄幼苗漂走的数量最多。昆虫和螃蟹等动物的取食是导致林内已经固着生长的秋茄幼苗大量死亡的最主要原因，而林外被取食的幼苗个体极少。此后秋茄幼苗能否继续成长，主要取决于幼苗所接受到的光照条件。3a后，在荫蔽的树冠下，秋茄幼苗无法存活；而在林外，秋茄幼苗已经长成幼树。在林外滩涂上迅速生长的互花米草，也将影响秋茄幼苗的更新和生长。

The growth of Kandelia candel seedlings in mangrove habitats of the Zhangjiang Estuary in Fujian Province,China

To evaluate the establishment and early growth of the mangrove species Kandelia candel in the intertidal zone,and to develop a better understanding of biotic and abiotic factors influencing the regeneration of its seedlings,we conducted a field experiment in Zhangjiang Estuary in Fujian.Different positions along the intertidal gradient were selected from 20 m to 120 m horizontal distance down the shore,including eight sampling sites in the mangrove areas.Equal numbers(75) numbers of mature propagules of K.candel were planted in each sampling site.The fates of propagules and growth of seedlings were monitored for 3 years.The rates of rooting of K.candel propagule varied spatially.The lowest rates occurred in sites with an Avicennia marina-dominated overstory(69.7%).The rates were higher in sampling sites with a K.candel-dominated overstory(90.0%),at the fringe of the mangrove forest(89.3%),and on the bare tidal flat outside the mangrove forest(82.7%).After 1 year,the survival rates of seedlings planted under A.marina forest,K.candel forest,at the fringe of the mangrove forest, and the bare tidal flat were 13.7%,54.7%,76.0%,and 34.7%,respectively.Among the surviving K.candel seedlings,those at the fringe of the mangrove forest and on the bare tidal flat had greater height,stem diameter,leaf number,leaf area,and biomass than did those under the A.marina and K.candel forests.In general,our experiment demonstrated that establishment and growth of K.candel seedlings occurred successfully at the fringe of the mangrove forest but did worst under the A.marina forest.We analyzed the factors which translate K.candel seedlings' performance into significant differences in terms of establishment and early growth among sites.The performance of K.candel seedlings was not correlated with sediment texture,pH,salinity,organic matter,total N,and total P among the sites.However,interspecies competition,propagule predation by insects and crabs,and the incident light had significant effects on seedling survival and growth.At the early growth stage,the probability of establishment of K.candel propagules planted in the intertidal sediments was influenced by predators and tidal disturbance.Under the A.marina forest,the compact root system of A.marina prevents K.candel propagules from rooting so that the propagules tend to be carried away by tidal currents.Insects and herbivorous crabs can play a considerable role in the predation of mangrove propagules and possibly are a threat to the regeneration of mangroves.We found that rates of insect and crab predation were higher in the intertidal location under intact canopies than at the fringe of the mangrove forest and on the bare tidal flat.Long-term survival of seedlings and their development into saplings depend on light availability.Analyses showed that correlation between growth parameters of one year old K.candel seedlings and light intensity was significant.Shade reduced seedling growth in the field.Only those seedlings at the fringe of the mangrove forest and bare tidal flat established successfully and grew to maturity.These sites afford better growth conditions than the surrounding understory and,as importantly,provide a refuge from predation by insects and crabs.Our results also indicate that the rapid growth of Spartina alterniflora reduces the regeneration of K.candel.As a competitive plant to K.candel in the mid intertidal zone,S.alterniflora may be having a large impact on the mangrove composition of our study forests.It is necessary to search for ways to protect this reserve area of mangrove wetland.