Experimental Ecology of Dryas Octopetala Ecotypes. III. Environmental Factors and Plant Growth

Abstract

Environmental factors responsible for differential growth and fitness in fellfield and snowbed ecotypes of Dryas octopetala were examined. Field manipulations to alter levels of nutrient availability, water availability, exposure, and competition were performed in 1979, 1980, and 1981. Factors associated with nutrient availability and competition had the greatest effect on growth in both ecotypes. However, shading and fertilization treatments had strong negative effects on fellfield plants, whereas snowbed plants were more shade-tolerant and growth increased in response to fertilization.

Relative effects of nutrients and light were examined further in a factorial experiment under controlled conditions. The two ecotypes responded differently to variation in light level, reaffirming the ecotypic difference in shade-tolerance. However, unlike the results of field fertilization, high nutrient availability did not differentially affect the two ecotypes. Therefore, the differential response of ecotypes to high nutrient availability in the field was most likely due to an increase in the biomass and productivity of the competitors of D. octopetala. Field and growth chamber studies suggested that the snowbed ecotype was better able to withstand the diminished light availability associated with increased competition.