| Water level was one of the important environmental factors that had an influence on wetland ecosystem and the growth and development and distribution of wetland plants. In recent years the wetland water level of Hangzhou bay fluctuated greatly because of human activities and global climate change. The wetland ecosystem had suffered from considerable damage with the wetland plant species decreased, so that the wetland animal habitat was destructed and seriously affected the steady state of wetland ecosystem. The change of the interaction relationship between wetland plants was one of the main factors of plant community change. Interspecific interaction played a very important role in wetland ecosystem. So the study that the interactions between species in the wetland community could make wetland community composition, community structure and community succession understanding well and provided certain theoretical basis for using reasonable resources, protecting biodiversity and wetland restoration and protection of the wetland plant.Interspecific interaction may modify the responses of aquatic plants to water level. Distribution, morphology and growth of two emergent aquatic plants, Phragmites australis and Typha domingensis, either in monoculture stands or in mixed stands, along a water level gradient in the artificial wetlands in the Hangzhou Bay area were investigated. Water level distribution and growth characteristics (leaf numbers, stem diameters, shoot height, density) were surveyed. The main findings and conclusions are as follows:1. It was found that P. australis plants from monoculture stands grew at shallow and medium water level (0-50 cm), while T. domingensis grew at deeper water level (20-60 cm). Mixed P. australis grew at shallow and medium water level (0-50 cm), and mixed T. domingensis in medium and deeper water level (20-100 cm). Water level imposed significant effects on the morphology and growth indexes of the P. australis and T. domingensis plants (p<0.05). With increasing water level, leaf number, stem diameter, shoot height and density of P. australis or T. domingensis plants from either monoculture stands or from mixed stands, all increased, followed by a decrease. Species coexistence had significant effects on leaf number, plant shoot of both species and stem diameters of P. australis (p<0.05). Compared to the monoculture stands, leaf number, stem diameter and density of the P. australis or T. domingensis plants from mixed stands was lower at the corresponding water level, but plant shoots height was higher. There were significant interaction effects between water level and species coexistence on growth of both species. The interaction effects were negative for leaf number of both species and stem diameters of P. australis and positive for shoot height of both species (p<0.05). The negative effects of species coexistence on leaf number of both species and stem diameter of P. australis, and the positive effects on shoot height of both species fluctuated along the water level gradient. These results indicated that P. australis and T. domingensis responded to water level and species coexistence and species coexistence will modify the responses of both species to water level.2. According to field investigation, the results showed that the growth of water level distributions of the Phragmites australis and Typha domingensis had overlapping part. In order to reveal the responses to water level gradients (0,20,40,60,80 cm) of wetland plants, the effects of water level gradient and coexistence on photosynthetic characteristics of the P. australis and T. domingensis were examined in this study. It was found that the biomass of P. australis increased followed by a decrease significantly in single populations with the increase of water level (p<0.05), while that of T. domingensis in single populations significantly decreased followed by an increase (p< 0.05).Compared with the single P. australis and T. domingensis, coexistence reduced the biomass of mixed P. australis and T. domingensis in different water level. The net photosynthetic rate, stomatal conductance, maximum net photosynthetic rate and light saturation point were not inhibited by the low water level and medium water level, but were significantly inhibited at deep water level. The effect on dark respiration rate was not significant, but increased obviously. Compared with single P. australis and T. domingensis, coexistence increased maximum net photosynthetic rate, apparent quantum efficiency and light saturation point and decreased light compensation point of the mixed P. australis and T. domingensis at medium water levels, illustrating that the species coexistence enhanced photosynthesis of medium water level in the mixed P. australis population. The maximum net photosynthetic rate, apparent quantum efficiency, stomatal conductance, intercellular CO2 concentration increased and light compensation point of T. domingensis decreased at deep water level, showing that the coexistence enhanced the photosynthesis of T. domingensis deep water level. The research results showed that water level improved the photosynthesis of the P. australis and T. domingensis. The species coexistence, respectively, improved the photosynthesis at medium water level in the P. australis and deep water n the T. domingensis population.3. It was found that water level imposed significant effects on total biomass, the ground and underground biomass of P. australis and T. domingensis(p<0.05).With the increase of water level, gross dry weight and shoot biomass were the trend of first increasing before decreasing, while underground biomass was the opposite trend in the monoculture and mixed P. australis stands. Gross dry weight, shoot biomass and underground biomass were the trend of declined before increased in the monoculture and mixed T. domingensis stands. Species coexistence influenced on shoot biomass and underground biomass significantly in mixed P. australis and T. domingensis stands (p<0.05). The shoot biomass and underground biomass of the mixed P. australis in medium and deep water level (20-80cm) were less than the single population, while the shallow water level (Ocm) was on the contrary. The shoot biomass and underground biomass of the mixed T. domingensis at 60 cm water level was higher than the single population, and other water level was less. The interaction of the water level and species coexistence had an significant influence on gross, shoot, underground biomass and root-shoot ratio of P. australis and T. domingensis populations (p<0.05). The positive effects of species coexistence on gross dry weight, shoot biomass and underground biomass of P. australisat at Ocm water level and on gross dry weight, shoot biomass at 60cm and underground biomass at Ocm and 60cm of T. domingensis fluctuated along the water level gradient. The positive affects on root-shoot ratio of P. australisat with fluctuation changes, while the negative effects on root-shoot ratio of T. domingensis. |
PDF Full Text Request