Reproductive Allocation

Summary • This study was conducted to determine whether elevated CO 2 alters patterns of plant reproduction, and whether density affects population- and individual-level responses to elevated CO 2 . • Phytolacca americana was grown in a glasshouse at three population densities under ambient and elevated CO 2 environments, and harvested at both vegetative and seed mature stages. •C O

Plastic responses to stress in components of reproduction can have important effects on plant fitness and can vary both within and between species. Responses may also depend on when in the life cycle stress occurs. Here, it is predicted that the timing of initiation of a stress, defoliation, would affect the pattern of plastic responses. These differences should occur because some components of reproduction, such as flower number, are determined earlier in a plant's life than others, such as individual seed mass. To test this prediction, 50 % artificial defoliation treatments were initiated at four different times for Sesbania macrocarpa and S. vesicaria. Responses were measured in plant size, number of flowers, number of flowers/plant size, fruit set, number of seeds per fruit, individual seed mass and total seed mass per plant. For S. vesicaria, changes in the timing of stress changed the severity, but not the pattern of response. For S. macrocarpa, plastic responses to defoli...

Three tallgrass prairie plant species, two common perennial forbs (Artemisia ludoviciana and Aster ericoides (Asteraceae)) and a dominant C4 perennial grass (Sorghastrum nutans) were studied under field and greenhouse conditions to evaluate interspecific variation in grazing tolerance (compensatory growth capacity). Adaptation to ungulate grazing was also assessed by comparing defoliation responses of plants from populations with a 25-yr history of