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 environment, selection may favor genetic variants with a well-developed ability to store resources for future vegetative growth or to regrow following herbivory. To determine the evolutionary potential for changes in vegetative growth, storage and regrowth after defoliation in response to competitive stress, half-sib families of the caespitose grass Phleum pratense were grown in pots in a glasshouse either alone or in competition with four individuals of 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 recorded 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 significant variation among families for many variables. A significant proportion of the variation in clipped and regrowth leaf mass, and in stem base mass, was due to a competition by fan-lily interaction. Storage in stem bases was correlated with total accumulated leaf mass in both control and competition groups. Genetic variation for competitive ability and the ability to regrow rapidly after defoliation exist in this P. pratense population. A well-developed ability to regrow following release from competitive or grazing pressures is likely to be a critical adaptation of caespitose grasses.