Study On Soil Respiration Of Stipa Baicalensis Community And Water Physiological Characteristies Of Stipa Baicalensis On The Songnen Grasslands

Semi-arid meadow grassland was a vegetation form that developed under the transitional climate. As a typical community of semi-arid meadows grassland, the component species of Stipa baicalensis community are less than other communities in the same region. The community productivity, structure and succession are significantly influenced by global climate changes. This study focused on soil respiration rate of Stipa baicalensis grassland by using dynamic infrared gas absorbed method. We analyzed diurnal pattern of soil respiration rate and the influences of surface soil temperature and water content for this parameter, then compared the differences between day and night soil respiration rates, and explored the correlations between aboveground and underground biomass with the soil respiration. The major results were summarized as following: (a) The average soil respiration rate of Stipa baicalensis grassland was 4.16 1.08 gC-m-1d-1 during the growing season. The diurnal pattern of soil respiration rate had a single peak, the maximum value appeared at 10:00-13:00, and the minimum value appeared at 4:00-6:00; (b) The correlation between diurnal soil respiration rate variation and soil chamber air temperature was better than 10cm soil temperature; (c) The variatons in the chamber water vapor concentrations resulted from the interaction between the temperature and soil water content, so it had a significant correlation with the variation of soil respiration rate; (d) There were considerable significant differences between day and night soil respiration rates. For this study, the day soil respiration rates (averages of four months) were higher than the night soil respiration rates as 35.3%; (e) Above-ground biomass and under-groundbiomass were the main factors resulting to the variation in soil respiration on site.Plant photosynthesis and transpiration characteristics were more significantly influenced by CO2 enrichment, photosynthetic active radiation and climate warming. The variations of these ecological factors were the result of global climate changes. In order to explore the influence of ecological factors on plant physiological characteristics, we carried out a series of experiments on Stipa baicalensis community. With the increasing of CO2 concentrations, the transpiration rate of Stipa baicalensis, either for vegetative shoots or for reproductive shoots were significantly increasing. The average transpiration rates of vegetative shoots were 1.77 times sizes of reproductive shoots. The photosynthesis rates of both two types of shoots were obviously moving up with an increase of simulated CO2 concentrations. The average photosynthesis rate of vegetative shoots was 1.72 times sizes of reproductive shoots. Despite of differences in the physiological functions, the water use efficiency of vegetative and reproductive shoots had a linear increasing with the CO2 enrichment. So we draw a conclusion that CO2 enrichment can obviouely promote the water use efficiency of C3 plants. With intensifying of simulated photosynthetic radiation, the photosynthesis rates for all the shoots were increasing before radiation intensity reached 1200-1400 mol-m-2-s1 and 1000-1200 mol-m-2s-1 respectively for vegetative shoots and reproductive shoots. The average photosynthesis rate of vegetative shoots at all radiation gradients was 1.35 times sizes of reproductive shoots. The transpiration rates of shoots were increasing with the intensity of simulated photosynthetic radiation. As simulated photosynthetic radiation strengthened from 0 to 800 mol-m-2s-1, the water use efficiency of vegetative and reproductive shoots had a trend of suddenly increasing. With the constantly strengthen of simulated photosynthetic radiation, there had no significantly increasing of the water use efficiency, even a little bitdecreasing. We can draw another conclusion that the increasing of air pollution, smog and aerosol that result in reduce of photosynthetic active radiation would have no obvious influences on the photosynthetic accu...