Physiological Responses Of Bothrichloa Ischaemum And Artemisia Sacrorum To Rainfall Pulse In Loess Hilly-gully Region

Water is the main limiting factor of plant growth and distribution in loess hilly-gully region. Rainfall pattern changes will have a profound influence on environment, community structure and function in loess hilly-gully region under the background of global climate change. Understanding the rainfall response of natural grassland community will contribute to accurately assess the impact of ecological construction on grassland ecosystem, and provide theoretical basis for vegetation construction and recovery. Understanding the rainfall response of Bothrichloa ischaemum and Artemisia sacrorum is the basis for explaining the changes of community structure and function. Five different artificial precipitation events(0mm, 5mm, 15 mm, 35 mm and 50mm) were applied to natural grassland community, which was dominated by B. ischaemum(C4 grass) and A. sacrorum(C3 subshrub), during the dry season(in June) and the rainy season(in July) in loess hilly-gully region. Soil moisture, gas exchange parameters and leaf water potential of B. ischaemum and A. sacrorum under different precipitation events were monitored and analysed. The main conclusions were as follows:1. Rainfall pulses fluctuated soil moisture in June more than in July, and significantly affected soil moisture beween 0-60 cm layers both in B. ischaemum and A. sacrorum. The soil depth of infiltration was 60 cm.2. Both B. ischaemum and A. sacrorum showed significant increase trend in net photosynthetic rate, transpiration rate, intercellular CO2 concentrations, stomatal conductance and leaf water potential after rain pulses, but limiting value of stomata decreased siglificantly after rain pulses, and the response level and time of duration increased with the increase of rainfall amount. There was significance in net photosynthetic rate, transpiration rate, intercellular CO2 concentrations, stomatal conductance and limiting value of stomata 7 days after 50 mm rainfall, and 50 mm rainfall was still in response threshold.3. The response of soil water moisture, gas exchange parameters and leaf water potential after rain pulses in B. ischaemum is quicker than in A. sacrorum, and B. ischaemum could response significantly even under smaller rain pulses.4. There was a significant linear relationship between net photosynthetic rate, transpiration rate, stomatal conductance and leaf water potential with soil water content for both B. ischaemum and A. sacrorum within 50 mm rainfall.