[Effects of water table manipulation on leaf photosynthesis, morphology and growth of Phragmites australis and Imperata cylindrica in the reclaimed tidal wetland at Dongtan of Chongming Island, China].

During the growing season of 2011, the leaf photosynthesis, morphological and growth traits of Phragmites australis and Imperata cylindrica were investigated along a gradient of water table (low, medium and high) in the reclaimed tidal wetland at the Dongtan of Chongming Island in the Yangtze Estuary of China. A series of soil factors, i. e., soil temperature, moisture, salinity and inorganic nitrogen content, were also measured. During the peak growing season, leaf photosynthetic capacity of P. australis in the wetland with high water table was significantly lower than those in the wetland with low and medium water tables, and no difference was observed in leaf photosynthetic capacity of I. cylindrica at the three water tables. During the entire growing season, at the shoot level, the morphological and growth traits of P. australis got the optimum in the wetland with medium water table, but most of the morphological and growth traits of I. cylindrica had no significant differences at the three water tables. At the population level, the shoot density, leaf area index and aboveground biomass per unit area were the highest in the wetland with high water table for P. australis, but all of the three traits were the highest in the wetland with low water table for I. cylindrica. At the early growing season, the rhizome biomass of P. australis in the 0-20 cm soil layer had no difference at the three water tables, and the rhizome biomass of I. cylindrica in the 0-20 cm soil layer in the wetland with high water table was significantly lower than those in the wetland with low and medium water table. As a native hygrophyte before the reclamation, the variations of performances of P. australis at the three water tables were probably attributed to the differences in the soil factors as well as the intensity of competition from I. cylindrica. To appropriately manipulate water table in the reclaimed tidal wetland may restrict the growth and propagation of the mesophyte I. cylindrica, and facilitate the restoration of P. australis-dominated marsh plant community.

[Effects of water table manipulation on the soil respiration in a reclaimed tidal wetland at Dongtan of Chongming Island, China].

From January 2011 to January 2012, a monitoring was made on the soil respiration rate and its major affecting environmental factors along a gradient of water table (low, medium and high) in a reclaimed tidal wetland at the Dongtan of Chongming Island in the Yangtze Estuary of China. The annual soil respiration rate in the wetland with low, medium and high water table was 0.75-11.57, 0.70-12.61, and 0.83-6.67 micromol x m(-2) x s(-1), respectively. The soil respiration rate was the maximum in July and the minimum in January. The soil temperature in 0-5 cm layer was the key microclimate factor driving the soil respiration across the three gradients, which could explain more than 70% of the seasonal variation of soil respiration in the reclaimed tidal wetland by fitting an exponential model. No significant difference was observed in the temperature sensitivity of soil respiration (Q10 value) among the three gradients. The lowest soil respiration rate in the wetland with high water table was probably due to the lower soil temperature and the higher soil volumetric water content, whereas the higher soil respiration rate in the wetland with medium water table than with low water table could be caused by the lower soil electricity conductivity and bulk density and the higher aboveground biomass and live fine root density. To appropriately manipulate the water table in the reclaimed tidal wetland could decrease soil respiration rate and enhance the carbon sink function of this degraded wetland.