河口盐沼植物分布对有效光合辐射的响应

对东滩植被带光量子通量密度的调查研究表明:互花米草带与海三棱藨草带光量子通量密度没有显著性差异,其值分别为1 570和1 556μmol/(m2·s)。光照对两物种的生长、繁殖等植物行为的影响只取决于其对光照的利用能力和效率;在互花米草和海三棱藨草混生带,到达互花米草和海三棱藨草的光量子通量密度之间存在显著差异(P0.05),互花米草对海三棱藨草的遮荫效应达63%,表明互花米草对海三棱藨草具有强的遮荫作用。光照不足严重影响海三棱藨草的生长,在混生带,海三棱藨草生长速率降低,种群密度和生物量减少,植株高度增加。因此,互花米草对海三棱藨草的遮荫作用,抑制了海三棱藨草在中潮滩的更新过程,因而也是造成海三棱藨草生境丧失的重要原因之一。

RESPONSE OF PLANT DISTRIBUTION TOPHOTON FLUX DENSITY IN SALT MARSH OF DONGTAN WETLANDS IN YANGTZE RIVER ESTUARY

Light is one of the main environmental factors influencing plant growth and distribution. In natural conditions, high plant usually shades the adjacent species, which inhibit the growth of some ambient species. The light intensity partially affects the condition of habitat, such as surface evaporation and salinity. Consequently, available light will probably structure plant community in some regions. In order to understand how does light affect the distribution of Spartina alterniflora and Scirpus mariqueter in Yangtze River estuarine salt marsh, we explored the response of plant distribution to photon flux density (PFD) in different vegetation zones at the salt marsh of the Chongming Dongtan. The results showed as follows. 〖JP2〗The photon flux density was 1 570 μmol/（m2·s） in the Spartina zone, and 1 556 μmol/〖JP〗（m2·s） in Scirpus zone. In the core zones of Spartina and Scirpus, the effect of light on plant growth and reproduction depended on the capacity and efficiency of using light. However, in the mixed zone of Spartina and Scirpus, the photon flux density on the top of Spartina was significantly greater than that on the top of Scirpus, with the value of 1 398 μmol/（m2·s） and 601 μmol/(m2·s), respectively. Spartina shaded 63% of lights of reaching the top of Scirpus in the mixed zone. With the increase of biomass and height of Spartina, relative shading effect of Spartina on Scirpus was significantly increased(P<0.05). The deficiency of light significantly affected the colonization and distribution of Scirpus in the mixed zone, such as low relative growth rate, and decreased biomass and density. As a result, the shading effect of Spartina constrains the distribution of the upper Scirpus, which further resulted in the loss of habitat of Scirpus adjacent to the exotic Spartina.