Abstract:

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.