The competitive ability of two natural populations of Dactylis glomerata, one from Norway and the other from Portugal, was investigated by growing them in monoculture and together in a mixed sward under different temperature and light regimes. At 7 ◦C and 8 h photoperiod, the performance of the prostrate Norwegian population grown in mixture with the erect Portuguese population was suppressed as compared with its performance in monoculture. However, at 30 ◦C and 16 h photoperiod, when the growth habits of these two populations were reversed in comparison to those at 7 ◦C, the dry weight per plant of the erect Norwegian population was significantly greater in the mixed sward than in monoculture. The dry weight per plant of the Portuguese population did not differ significantly in the two types of sward at either temperature. The results are discussed in relation to competition for light. © 1969, Cambridge University Press. All rights reserved.
