Costs of Reproduction in the Pink Lady's Slipper Orchid (Cypripedium acaule): Defoliation, Increased Fruit Production, and Fire

Abstract

An earlier experiment with the pink lady's slipper orchid demonstrated that plant leaf area was lowered only after successive years of increased fruit production. This result suggested that the cost of reproduction was small in relation to the energy budget of the plant. To test this idea, plants were subjected to experimental hand-pollination treatments to increase fruit set as well as leaf removal treatments to decrease the energy budget of plants. Changes in plant size in years 2 and 3 and, to some extent, rate of flowering, were determined by a combination of initial plant size, leaf removal treatments in year 1, fruit production in year 1, and damage from an unplanned fire in year 2. Plants that had both leaves removed and produced a fruit in 1987 decreased in size in the following 2 years in comparison with other treatment groups. The cost of fruit production was not apparent in plants that had only one or no leaves removed. Plants apparently have to be put into severe physiological stress in order for a cost of reproduction to appear in the following year. The cost of producing one fruit was a decline of plant size in the following year of 30 cm2, which is very similar to our previous experiment using a different design. An additional experiment failed to find evidence that these plants increase their photosynthetic rate to compensate for the loss of leaves or the cost of maturing fruit. Published experiments in both the greenhouse and the field that failed to find a cost of reproduction should be reevaluated in terms of the intensity of treatment imposed and the overall energy budget of the plant in field situations.