Abstract: Agropyron elongatum seedlings were exposed to different concentration Ni to study their growth and the changes in MDA and soluble protein contents and  SOD, POD and CAT activities in their shoots and roots, and the photosynthetic pigment content in their leaves. Low concentration (10 μmol·L^-1) Ni had no significant inhibitory effects on the seedlings growth, but the growth indices decreased significantly with increasing Ni concentration, being more markedly for roots than for shoots. The leaf photosynthetic pigment content had a decreasing trend with increasing Ni concentration, while the MDA content in shoots and roots had significant positive correlation with Ni concentration. The soluble protein content in roots increased with increasing Ni concentration. Under low concentration (10 μmol·L^-1) Ni, the SOD, POD and CAT activities all increased, and the protective enzyme system was well balanced. When the Ni concentration was increasing, the three enzyme activities were inhibited to different extents, and the balance of protective enzyme system was broken.

Key words: Photosynthesis of crop community, CO₂ flux density, Water use efficiency, Winter wheat