UV-screening and springtime recovery of photosynthetic capacity in leaves of Vaccinium vitis-idaea above and below the snow pack.

Abstract Evergreen plants in boreal biomes undergo seasonal hardening and dehardening adjusting their photosynthetic capacity and photoprotection; acclimating to seasonal changes in temperature and irradiance. Leaf epidermal ultraviolet (UV)-screening by flavonols responds to solar radiation, perceived in part through increased ultraviolet-B (UV-B) radiation, and is a candidate trait to provide cross-photoprotection. At Hyytiälä Forestry Station, central Finland, we examined whether the accumulation of flavonols was higher in leaves of Vaccinium vitis-idaea L. growing above the snowpack compared with those below the snowpack. We found that leaves exposed to colder temperatures and higher solar radiation towards the top of hummocks suffered greater photoinhibition than those at the base of hummocks. Epidermal UV-screening was highest in upper-hummock leaves, particularly during winter when lower leaves were beneath the snowpack. There was also a negative relationship between indices of flavonols and anthocyanins across all leaves suggesting fine-tuning of flavonoid composition for screening vs. antioxidant activity in response to temperature and irradiance. However, the positive correlation between the maximum quantum yield of photosystem II photochemistry (F v / F m) and flavonol accumulation in upper hummock leaves during dehardening did not confer on them any greater cross-protection than would be expected from the general relationship of F v / F m with temperature and irradiance (throughout the hummocks). Irrespective of timing of snow-melt, photosynthesis fully recovered in all leaves, suggesting that V. vitis-idaea has the potential to exploit the continuing trend for longer growing seasons in central Finland without incurring significant impairment from reduced duration of snow cover. Graphical abstract Schematic representing the changes in leaf level processes affected by the snowpack, sunlight and temperature at different heights on hummocks of V. vitis-idaea during spring dehardening. Image 1 Highlights • Leaf epidermal UV-screening increases from the base to the top of Vaccinium hummocks • Leaf epidermal flavonols and anthocyanins accumulate during spring dehardening • F v / F m was positively correlated with 2-week mean temperature during spring dehardening • Adaxial epidermal flavonols conferred cross-protection during dehardening [ABSTRACT FROM AUTHOR]