Effects of competitive stress on vegetative growth, storage, and regrowth after defoliation in Phleum pratense

The capacity for resource storage is important to population persistence in nonforaging plants with a consolidation strategy. In a competitive environ ment, selection may favor genetic variants with a well-developed ability to store resources for future vegetative growth or to regrow following herbiv ory. To determine the evolutionary potential for changes in vegetative grow th, storage and regrowth after defoliation in response to competitive stres s, half-sib families of the caespitose grass Phleum pratense were grown in pots in a glasshouse either alone or in competition with four individuals o f Lolium perenne. They were defoliated after 16 wk and permitted to regrow for 8 wk. Production of new tillers, leaf area and leaf dry mass were recor ded before and after defoliation; resource storage was estimated by the dry mass of stem bases. Tiller numbers, leaf area and mass, regrowth, and stem base mass were significantly reduced by competition: however, there was si gnificant variation among families for many variables. A significant propor tion of the variation in clipped and regrowth leaf mass, and in stem base m ass, was due to a competition by fan-lily interaction. Storage in stem base s was correlated with total accumulated leaf mass in both control and compe tition groups. Genetic variation for competitive ability and the ability to regrow rapidly after defoliation exist in this P. pratense population. A w ell-developed ability to regrow following release from competitive or grazi ng pressures is likely to be a critical adaptation of caespitose grasses.