The Effects Of Grazing On Water Use Efficiency Of Dominant Plants In Typical Steppe

Water is an important determinant factor of grassland ecosystem productivity. As a major use of natural grasslands, to some extent, grazing will often have some impact on grassland ecosystem carbon cycle and water cycle. Thoroughly revealing the impact of grazing on the grassland ecosystem water use efficiency (WUE) will help to understand the mechanism of degradation of grassland ecosystem from a plant individual and community level water metabolism angle. In this paper, we used Li-6400 portable photosynthesis meter and other equipment to measure and analyze the effects of different grazing intensity on Stipa grandis and Leymus chinensis about the photosynthesis characteristics, instantaneous water use efficiency and intrinsic water use efficiency in the leaf level in Inner Mongolia typical steppe; Meanwhile, we also measured and analyzed the effects of different grazing intensity on community photosynthetic, community respiratory and water use efficiency on community scales.The main findings are as follows:1. Moderate grazing will increase net photosynthetic rate of Stipa grandis; Grazing have no significant effect on net photosynthetic rate of Leymus chinensis. From the early to the late growing season, the net photosynthetic rate of two plants is decreasing.2. Moderate grazing and server grazing disturbance will increase Stipa grandis and Leymus chinensis’s stomatal conductance and transpiration rate; From the early to the late growing season, the two plants’stomatal conductance and transpiration rate tended to decrease.3. With grazing intensity increased, Stipa grandis’instantaneous water use efficiency (WUEt) tends to increase, while Leymus chinensis’s instantaneous water use efficiency shows a downward trend; From the early to the late growing season, the two plants’WUEt also showed an increasing trend. Intrinsic water use efficiency (WUEi) of leaves of two plants showed a downward trend with grazing intensity increased, but they were no significant change in each month of growing season.4. From the early to the late growing season, community net ecosystem carbon exchange capacity (NEE), ecosystem respiration (ER), the gross ecosystem productivity (GEP) and ecosystem evapotranspiration (ET) tended to decrease; a certain level of grazing will promote the community NEE and GEP and inhibit the community ER.5. Typical steppe community water use efficiency (WUE) seasonal variation is not obvious, but moderate grazing will improve water use efficiency of community.