Abstract
In order to clarify how much intraspecific variation in competitive ability exist in single grass species and which traits are responsible for it, we compared competitive ability of eighteen cultivars of D. glomerata when combined with weakly and strongly competitive cultivars of tall fescue (Festuca arundinacea Schreb.) for a period of two years under fertile soil conditions in experimental fields. Shoot and root morphological traits of each cultivar were also measured under pot conditions. Relative competitive ability was assessed by aggressivity, 1/2 (relative yield of focal species-relative yield of neighbouring species). The results obtained were as follows : (1) There were large differences in competitive ability between cultivars in both D. glomerata and F. arundinacea. The difference was more apparent in the second year than in the first year. (2) For D. glomerata, competitive ability in the first year was correlated only with the seedling emergence time. In the second year, most of the variation in competitive ability between cultivars was explained by shoot and root morphological traits. Competitive ability correlated positively with root DW, mean tiller weight and mean root weight. (3) For F. arundinacea, the strongly competitive cultivar had larger seeds, faster seedling emergence, larger root weight but smaller shoot DW than the weakly competitive cultivar.
