ORIGINAL ARTICLE

Abstract Livestock grazing represents a major human disturbance to grasslands throughout the world. We evaluated the effects of long-term grazing (>20 years) on a dominant perennial grass species, Leymus chinensis (Trin.) Tzvel., in the semiarid grassland of Inner Mon-golia, China, in terms of its morphological and func-tional responses. L. chinensis, one of the most abundant species in semiarid grassland, had significantly smaller leaf area, fewer vegetative tillers and shorter shoot in-ternodes length, but significantly greater specific leaf area for the individuals in the grazing plot than those in the exclosure (grazing-free) plot. Long-term grazing also altered the relative distribution of biomass to leaves, roots and rhizomes. The biomass, coverage and the number of species were lower in the grazing plot by 50– 70 % in comparison with those in the grazing-free plot. In addition, the long-term grazing substantively de-creased the physiological capacities of this grass species, including significantly lower net photosynthetic rate, apparent quantum efficiency, photochemical efficiency of PSII and water use efficiency. Significantly higher stable oxygen isotope ratios (d18O) of the soil water in the grazing plot than those in the grazing-free plot indicated a much higher soil evaporation in the grazing plot because of less litter coverage. Seasonal patterns in the d18O values of the stem water of L. chinensis and three other common species in the grazing and grazing-free plots indicated that plants in the grazing and graz-ing-free plots might shift their water sources differently from a dry month (June) to a wet month (August). This study illustrated the importance of using different ap-proaches to study the possible responses of grass species in arid regions to human disturbances, such as long-term grazing