By measuring and comparing the contents of amino acids in Agropyron cristatum under grazing pressure, this study showed that the contents of total and each of the amino acids in A. cristatum changed little under grazing pressure. How- ever, the contents of free glycine （Gly） and proline （Pro） were very sensitive to grazing. Glycine content in grazing population was higher than that in non-grazing population at flowering stage; the content of free proline in non-grazing population was higher than that in grazing population at tillering, heading and especially flower- ing stage; the content of free proline under grazing pressure at maturity stage was higher than that of non-grazing population.
[Objective] This study was conducted to explore the mechanism of physi- ological adaptation of Agropyron cristatum under grazing pressure, and to provide a theoretical basis for the protection and rational utilization of forage resources, breeding and introduction of high-quality forage materials. [Method] The mature leaves of upper parts of A. cristatum plants in grazed and non-grazed areas were collected at tillering （late May）, heading （late June）, flowering （late July） and seed maturity （late August） stages for determination of superoxide dismutase （SOD）, peroxidase （POD） activities and malondialdehyde （MDA） content. [Result] The MDA content of grazing population was higher than that of non-grazing population throughout the whole growth period of A. cristatum. The SOD activity was significantly increased from heading to flowering stage but was rapidly reduced at seed maturity stage, with no significant difference between grazing and non-grazing populations of A. cristatum. The POD activity kept increasing from heading stage, and it was higher of grazing population than that of non-grazing population. [Conclusion] The MDA content in leaves of A. cristatum was increased under grazing pressure, leading to increased membrane lipid oxidation; POD played an important role in removal of the free radicals those accumulated in A. cristatum under grazing pressure.
