RESPONSES OF THE SPRING EPHEMERAL CLAYTONIA-VIRGINICA L TO LIGHT AND NUTRIENT MANIPULATIONS AND IMPLICATIONS FOR THE VERNAL-DAM HYPOTHESIS

The effects of shading and fertilization on the ecophysiology of the s pring ephemeral Claytonia virginica L. (Portulacaceae) were examined i n the field. A two-way factorial design with main factors of light tre atment (ambient control irradiance vs. 90% attenuation) and nutrient t reatment (unfertilized control vs. 192 kg ha-1 total N, P2O5, and K2O equivalents added) was employed at Radnor Lake, TN. Plant shading redu ced biomass development, enhanced tissue nutrient concentration, and r educed both specific leaf weight and ribulose bisphosphate carboxylase /oxygenase (RUBISCO) activity relative to unshaded controls. Fertiliza tion enhanced aboveground nonreproductive biomass, elevated tissue nut rient concentration for N and P but not K, and increased the leaf widt h/length index relative to controls. Of greatest ecophysiological impo rtance were significant light by nutrient interactions where the stimu lation of both aboveground productivity and RUBISCO activity in respon se to fertilization occurred only for plants in unshaded, high-irradia nce conditions. These results suggest that C. virginica may be nutrien t limited under ambient field conditions, is not capable of acclimatio n to low-irradiance, that irradiance and nutrient availability interac t synergistically to affect the magnitude of short-term nutrient seque stering in C. virginica biomass, and imply that total nutrient capture by the ''vernal dam'' may adjust to variation in early-season nutrien t conditions to affect forest-wide nutrient conservation.