Ecological Study Of Spartina Alterniflora In Mangroves Habitats

Spartina alterniflora Loisel., a perennial grass, belongs to Spartina Schreb. in Gramineae. The originally purpose of introducing this species to many ocean countries and regions was to protect the beach environment, to improve soil properties and to make beach green due to its high tolerate ability to salinity and flooding, strong reproductive capacity and developmental root system. But now it is growing out of control and causes serious damages to the intertidal zone system.Mangroves are one of the most important primary producer in intertidal marine system, they have high biomass, litter production and high rate of energy flow and material circulation,and thus mangroves are an important food and energy sources in the estuarine and coastal systems. In Guangxi, S. alterniflora was first introduced in National Shankou Mangrove Nature Reserve in 1979, and has played an important role in preventing wind and wave, protecting beach erosion and promoting siltation. But in the last few years, S. alterniflora has gradually spread into neighboring mangrove communities and caused a large quantity of damage to the ecological system in the National Shankou Mangrove Nature Reserve. In this paper, the growth rules and reproductive characteristics of S. alterniflora in mangrove habitat were studied in order to provide some strategies to control its invasion. For this purpose, field dynamic monitoring investigation and indoor cultivation experiment were employed to make a systematic research on the morphological factor, biomass dynamics, photosynthesis, biomass dynamics in reproductive period and characteristics of reproductive organs of S. altemiflora in different mangrove habitats (clay, loam, and sand). The results obtained are as follows:1. Mangrove habitat has a significant effect on the biomass and morphological characteristics of S. alterniflora. Among the three habitats, individuals of S. alterniflora growing in clay habitat had the highest density and biomass. But in terms of morphological factors, the individuals of S. alterniflora grows best in the loam habitat than that of other two habitats. There was no significant difference between clay and sand habitats except for the under-ground biomass. Difference was exsited in biomass allocation among the three habitats. Soil porosity and nutrient content might be account to the difference of biomass and other morphological factos of S. alterniflora in three habitats.2. The biomass dynamics of S. alterniflora during the sexual propagation period were also studied in this paper. The results showed that: at the beginning of reproduction,the biomass of different organs increased respectively in various degrees with the time; but in the late of reproductive stage,the growth rates of root,stem and leaf biomass are negative, the negative biomass of stem was induced by the negative biomass growth rate of root and stem. The order of organs biomass is: stem> leaf>root>reproductive organ except in june; With the time goes by, the rate of root biomass decreased from 28.9% in June to 14.0% in November, while the ratio of stem biomass : total biomass was increased with the time goes by. The leaf biomass decrease slowly due to the physiologic aging. In a word, the biomass of reproductive organs only take a few part in the total biomass.3. The diurnal variation of net photosynthetic rate of S. alterniflora was a double peak curves and had a significant depression in the midday. Stomatal conductance(Gs) and transpiration rate (E) of S. alterniflora displayed single-apex curves. An significant negative correlation was exsited between intercellular CO2 concentration(Ci) and net photosynthetic rate. It was suggested that non-stomatal factors were the major causes of midday depression. The peak value of light intensity, temperature, stomatal conductance and transpiration rate appeared at 12:00, all environment factors could influence the net photosynthetic rate of S. alterniflora, and photosynthesis was controlled by stomatal factor and non - stomatal factor. The stomatal conductance dynamics of S. alterniflora growing in loamy mangrove habitat, was studied from noon to evening (ebb tide), and meanwhile, the relevant environmental factors were measured and analyzed. The results showed that: the stomatal conductance in different part of the plant varied vertically, i.e., the opening of leaf stomatal conductance was upper part>top>lower-middle part>under part. The leaf stomatal conductance had a relationship of power function to the light intensity and leaf temperature, but a negative exponential function with the time and relative humidity (RH). The stomatal conductance opening was biggest with humidity at 50%~60%, but with the increase of humidity the stomatal conductance became smaller. The leaves located at the middle part had the largest contribution to accumulation of photosynthate in the whole plant. The interaction of diverse environmental factors affected the stomatal opening and closure, and thus, its dynamic change can be viewed as a comprehensive response to environmental parameters.4. The morphological and quantitative characteristics, as well as the weight of 100 full seeds at maturity stage of S. alterniflora in three different habitats were studied in this paper. The results showed that: S. alterniflora had the best grow patterns in the loam habitat,the morphological factors of fructification of S. alterniflora grown in sand were larger than other habitats;The order of quantitative characteristics of fructification in the three habitats were clay>sand>loam; The variance analysis results showed that: In sand habitats, except length there were significant difference in all morphological factors to the other two habitats; length of second spikelet were longer than length of first spikelet in three habitats; the plumpness of seed at spikelet apical were higher than the button.5. The invation of S. alterniflora has caused large quantity of damage to the ecology system in the National Shankou Mangrove Nature Reserve. It's necessary to pay high attention to the problems caused by the invasion of S. alterniflora in this area and comprehensive preventing methods should be applied to prohibiting its invasion.