Response Of Community Characteristics To Artificial Water Suppliment In Natural Grassland At Loess Hilly-Gully Region

Precipatition is the most important factor that influences the structure and function of plant community at arid and semiarid regions. To study the response of plant community to precipatition pattern can predict the evolution tendency under future climate change conditions and provide scientific theory basis to vegetation restoration and grassland construction in such areas. This research was conducted at loess hilly-gully region of Loess Plateau and chose the Bothriochloa ischaemum donminated grassland community as research object. The species diversity, species richness and evenness, and productivity of the community were compared and investigated under artificial water supplyment in three frequency [water supplyment in July (M1); water supplyment in August (M2); water supplyment in both July and August (M3)] and two gradients [improved10%(W1) and20%(W2) according to average soil water content in0-100cm soil depth]. At the smane time, precipitation is redistributed by the complicate topography at loess hilly-gully region, thus in order to analyze the response of plant community characteristics to landform chande comprehensively and accurately, one investigation was conducted at three locations to study the grassland community whose dominant species are Bothriochloa ischaemum or Lespedeza davurica. The main results are as below:1. The species important value and dominance index were improved under artificial water supplyment, comparing with CK. The dominance index ratio of Bothriochloa ischaemum was improved from15.9%to21.0%under M1W1treatment, and the ratio of Stipa bungeana increased from6.5%to14.3%under M2W1treatment. While the dominance ratio of Lespedeza davurica decreased from16.5%to13.7%under M2W2treatment. Results showed that there were no significant trends in the dominance index change under different water supplyment gradients and time treatments.2. The Shannon-wiener and species richness index increased significant under water supplyment. The biomass production of community was significantly improved than the biodiversity index and species richness index. Water supplyment time had siginifcant effects on community characteristics, and the water supplyment in July showed higher species diversity inder and productivity.3. The soil CO2emissions daily dynamic of in June and August were single-peak curve. Water supplyment significantly improved the soil respiration rate of Bothrichloa ischaemum community. After analyzing the relationship between soil/air temperature and soil respiration rate, it showed that soil respiration rate was closely related with air temperature and5cm soil temperature. Results also showed that air temperature can explain83.3%the variation of soil respiration rate in Bothrichloa ischaemum community(CK), while under water supplyment community the rate was only75.2%(W2) and16.7%(W1). All these suggested that the sensitivity of soil respiration to temperature was decreased by soil water improvement.4. The field investigation results showed that, the soil water content and biomass production had similar changing trend under different slope positions. Correlation analysis indicated that there was a positive correlation between soil water content and aboveground biomass production. It suggested that in the loess hilly-gully region, slope position redistributed precipitation and thus affected plant growth and community succession, and also the community characteristics such as species diversity, species richness and evenness and productivity.