Differences in Microsite, Plant Form, and Low-Temperature Photoinhibition in Alpine Plants

Abstract

Low temperatures and high sunlight, factors that are characteristic of high elevations, may lead to the low-temperature photoinhibition of photosynthesis (LTP). Exposure and photosynthetic responses to low temperature and high sunlight were compared among current-year seedlings of the conifers Abies lasiocarpa and Picea engelmannii, and the snowbank perennials Caltha leptosepala and Erythronium grandiflorum, in the alpine treeline ecotone. The ratio of silhouette (sunlit) to total leaf area of whole plants was greatest in A. lasiocarpa (0.33), 25% lower in P. engelmannii (0.25), and at least 36% lower in the snowbank perennials than for A. lasiocarpa. This indicated less structural avoidance of high sunlight in the conifer seedlings, particularly A. lasiocarpa. CO₂ assimilation (A_sat) in A. lasiocarpa was reduced 40% due to frosts, high sunlight (22%), and their combination (90%). A_sat was much less affected by frosts and high sunlight in P. engelmannii and especially the perennials. Following frost and high sunlight exposure, diurnal reductions in maximum photosynthetic efficiency, indicated by the chlorophyll fluorescence ratio F_v/F_m, corresponded to species differences in A_sat. A substantially greater degree of slowly-reversible, or irreversible LTP (44% reduction in predawn F_v/F_m) occurred in the microclimate above snow for A. lasiocarpa compared to the other species. It appears that a higher resistance to LTP in the perennials may contribute to their greater occurrence in microsites with lower temperatures and higher sunlight compared to the conifer seedlings.