Effects of snowmelt on the springtime photosynthesis of the evergreen dwarf shrub Vaccinium vitis-idaea

Background: The dwarf shrub Vaccinium vitis-idaea has been found to retain its photosynthetic capacity under snow in winter. At snowmelt, the plants are exposed to low temperatures and full light, which may lead to the inhibition of photosynthesis. Aims: To examine the changes in the photosynthesis of V. vitis-idaea at snowmelt and to determine their temporal extent. Methods: The photosynthetic capacity and the energy conversion efficiency of photosystem II (Fv/Fm) were determined in a natural spring snowmelt setting in field conditions and by creating an artificial snowmelt gradient. Results: Fv/Fm decreased rapidly after snowmelt and remained low for several weeks in the spring. The photosynthetic capacity remained at pre-snowmelt levels at first, but started decreasing about a week after snowmelt. The depression of photosynthesis lasted for several weeks. Conclusions: The inhibition or downregulation of photosynthesis in V. vitis-idaea takes place at snowmelt, not at the onset of winter as it does in many evergreen conifers. The snow protects the plants from the harshest winter conditions and permits metabolic activity. If snow cover becomes more intermittent in the future, there may be longer periods of photoinhibition, which will affect the carbon balance of plants.