The Effect of Nitrogen and Clipping on Interference Between C 3 and C 4 Grasses

Abstract

(1) The effects of nitrogen deficiency and defoliation on the growth performance and competitive interactions of Agropyron smithii (C3) and Bouteloua gracilis (C4) were studied in pot experiments. (2) The results on the growth of nitrogen-deficient plants do not support the hypothesis that C4 plants have greater nitrogen efficiency than C3 species. (3) Temperature is a major factor influencing the outcome of competition. Agropyron smithii accumulates biomass faster than Bouteloua gracilis at 20 IC day/15 IC night conditions. The reverse is true at 30 ?C day/15 ?C night. (4) Bouteloua gracilis exhibits a greater resistance to defoliation than Agropyron smithii. The decrease in the crowding coefficient of Agropyron smithii with respect to Bouteloua gracilis and the increase of the coefficient of Bouteloua gracilis with respect to Agropyron smithii following clipping indicates that defoliation increases the competitive ability of Bouteloua gracilis. (5) These results suggest that there is a range of temperatures between 20-15 0C and 30-15 ?C in which defoliation results in a shift in competitive outcome.