PHYSIOLOGICAL SENSITIVITY OF PLANTS ALONG AN ELEVATIONAL GRADIENT TO UV‐B RADIATION

Abstract

Seeds from four plant pairs collected from contrasting elevations in Hawaii were grown in greenhouses at the University of Maryland at UV‐B radiation levels that approximated a 20% and 40% stratospheric ozone depletion anticipated at sea level in Maui. In general, increases in UV‐B radiation resulted in earlier reproductive effort, increased dark respiration and maintenance of relative water content (RWC), photosynthesis, and apparent quantum efficiency (AQE) in plants from higher elevations where natural UV‐B radiation is already high. In contrast, plants collected from low elevational ranges showed a significant decline in average plant and floral dry biomass, a decline in AQE and RWC, and a reduction in light‐saturated photosynthetic capacity. Increases in UV‐B‐absorbing compounds (e.g., flavonoids), were noted for low elevation but not high elevation plants. However, plants from high elevations produced a consistently larger amount of these compounds even in the absence of UV‐B radiation. This study suggests that plants growing in a naturally high UV‐B environment may have developed or maintained mechanisms related to reproductive phenology and carbon uptake which may maintain productivity in a high UV‐B environment. This would also suggest that ecotypic differentiation may have occurred in response to increasing UV‐B radiation over an elevational gradient. The range of adaptability to increased UV‐B also implies changes in species and community dynamics that might be anticipated in natural plant populations if stratospheric ozone depletion continues.