HOW IMPORTANT ARE ENVIRONMENTAL MATERNAL EFFECTS IN PLANTS - A STUDY WITH CENTAUREA-MACULOSA

1 Previous studies have reported significant influences of maternal en vironment on offspring fitness in plants. We investigated the early pl ant development from seeds of Centaurea maculosa plants grown in four environments of increasing severity: (1) control; (2) herbivory; (3) h erbivory + nutrient shortage; and (4) herbivory + nutrient shortage grass competition. 2 Although these treatments had huge effects on the size of the mother plants and the number of seeds they produced, ther e was no evidence that the treatments affected the weight of the seeds they produced. There was, however, significant variation in seed weig ht among maternal plants within treatments. 3 We grew individually wei ghed seeds from 33 of these maternal plants in three competitive regim es (individually, with one conspecific neighbour, with three Festuca p latensis neighbours) to test if maternal environment and seed weight i nfluenced first-year growth, and if these effects were more pronounced in the presence of competition. 4 There were a few weak but significa nt environmental maternal effects on offspring performance. Seed weigh t was positively correlated with initial growth, but its influence dec reased over time and disappeared after 8 weeks, The presence of one co nspecific neighbour or three Festuca pratensis neighbours did not infl uence growth during the first few weeks, but strongly suppressed growt h after 9 weeks. Competition did not accentuate the influence of seed weight on offspring performance. 5 Differences among individual matern al plants were a major source of variation in seed weight and early of fspring growth. Some of the evidence that has been cited in support of environmental maternal effects in plants may be the result of confoun ding maternal identity and maternal environment. 6 Our results support the generalization that seed size is one of the least plastic of plan t characters. Plants express great plasticity in reproductive output, but this occurs primarily in terms of the number of seeds produced, an d only secondarily, if at all, in terms of seed size or quality. 7 Eff ects of a plant's maternal environment on its performance can be detec ted, but they appear to be small compared to other factors that influe nce a plant's fitness, such as its genotype and the environment in whi ch it grows.