In arctic ecosystems, snow cover persists into the spring long after air temperatures and light levels may be suitable for vascular plant photosynthesis. However, the general assumption is that vascular plants under the snow show little if any photosynthetic activity. We have found that significant photosynthetic activity occurs in arctic evergreens in late spring prior to snowmelt, which in turn has implications in the ecosystemís carbon balance. This photosynthetic activity is quite variable and appears to be linked to microtopographic characteristics that affect photosynthetic photon flux densities (PPFD) reaching the plants. To protect their photosynthetic apparatus against the effects of high PPFD during spring melt, three arctic evergreens, Ledum palustre L., Vaccinium vitis-idaea L., and Cassiope tetragona L., were shown to produce significant concentrations of anthocyanins. The concentrations of anthocyanins were dependent on leaf positioning on individual plants and the position of individual plants within the microtopography. Plants that faced directly south tended to produce higher concentrations of anthocyanins than plants in shaded settings or northern orientations. We also demonstrate that snow load and anthocyanin concentrations are inversely correlated; as snow depth decreases and PPFD increase at the ground surface, concentrations of anthocyanins increase until moderate growing season conditions persist. These findings add additional support to the light screen hypothesis that suggests that anthocyanins protect photosynthetic tissues from photoinhibition when high light is coupled with low temperatures. This reduction in photoinhibition allows the species to increase their physiological activity prior to emerging from snow cover and allows them to reach maximum photosynthetic capacity within days of becoming snow free. This strategy is an important aspect of the acquisition of carbon reserves for these species during the short growing season.

Key words: anthocyanins, arctic evergreens, spring snow melt