Abstract: C₃ and C₄ forage plants in the Northeast stepps were identified by using the ratio of RuBPCase activity/PEPCase activity. 35 species among the total 45 tested species were first identified. The Kranz structure was observed only for Gramineae plants. On the basis of C₃ or C₄ plants identified, 11 dominant species were selected to study their geographical distribution, phenological spectrum and relationship between their relative dominance and soil pHvalue or salt content. The results showed that there were 30 species of C₃ plants from 24 genera in10 families and 15 species of C₄ plants from 9 genera in5 families. In comparison with C₃ plants, C₄ forage showed a higher relative growth dominance in the season with high temperature, strong radiation and high precipitation and a higher relative distribution dominance at lower latitudes and salt alkalized region. The correlation coefficient between relative dominance of C₄ forage and soil pHvalue, or salt content was 0.826 or 0.760 respectively, but that for C₃ plants was negative.

Key words: C₃ plant, C₄ plant, Activity of RuBPCase/PFP case, Fcelegical distritut