Comparing the ecophysiology of four tree species growing in the coastal temperate rainforests of Prince William Sound, Alaska.

摘要

This comparative study examines the ecophysiology of four endemic plant species abundant in the coastal temperate rainforests of Prince William Sound, Alaska. Photosynthesis in Alnus crispa ssp. sinuate (Betulaceae), Rubus spectabilis (Rosaceae), Vaccinium alaskaense and V. ovalifolium (Ericaceae) was measured with a MINI-Pulse Amplitude Modulated (PAM) fluorometer. A. sinuate (sun) and R. spectabilis (partial shade) had higher photosynthetic capacities (maximum apparent photosynthetic electron transport rates, ETR_max) and higher light saturation intensities (I_k) than V. alaskaense (partial shade) and V. ovalifolium (shade). A. sinuate was less sensitive to photoprotective down regulation through the xanthophyll cycle (qE) than R. spectabilis. Vaccinium species showed similar photosynthetic characteristics except V. ovalifolium was sensitive qE while V. alaskaense was not. A comparison of A. sinuate trees growing in the 'sun' versus 'shade' revealed sun trees had higher ETR_max and I_k than shade trees. High photochemical quenching (qP; 0.893-0.978), associated with photochemical productivity, measured along with low non-photochemical quenching (qN; 0.252-0.678) at I_k revealed shade plants are acclimated to low ambient light, and have limited use for qN. Nonetheless, at higher light intensities, all species are ready to safely dissipate excess light in non-photochemical quenching to heat based on qN (~0.6-0.8) and NPQ (~0.7-2.6). These findings illustrate the adaptive responses of plants growing at high latitudes with respect to photoacclimation. Differences between plants were correlated to their position along the natural light gradient created by the forest canopy.