Our results show that evergreen species, such as Vaccinium vitis-idaea, are capable of photosynthesizing under insulating snow cover. The subnivean photosynthesis compensates for respiratory CO2 losses during winter, and even net gain of carbon can be achieved. Consequently, the total concentration of non-structural carbohydrates may stay at a steady level in the overwintering leaves throughout winter.
At snowmelt photosynthesis is inhibited due to excessive levels of light and exposure to low temperatures when the protection of the snow cover is lost. Recovery of photosynthesis may take several weeks after snowmelt.
Our growth chamber experiments show that V. vitis-idaea is able to up-regulate its photosynthesis very rapidly when exposed above-zero temperatures in mid-winter. This suggests that the significance of photosynthetic activity in winter may increase along with warming winters.
Saarinen, T., Rasmus, S., Lundell, R., Kauppinen, O.-K. & Hänninen, H. 2016. Photosynthetic and phenological responses of dwarf shrubs to the depth and properties of snow. –Oikos 125:364-373. DOI: 10.1111/oik.02233
Åström, H., Metsovuori, E., Saarinen, T., Lundell, R. and Hänninen, H 2015. Morphological characteristics and photosynthetic capacity of Fragaria vesca L. winter and summer leaves. –Flora 215:33-39. DOI: 10.1016/j.flora.2015.07.001
Saarinen, T., Lundell, R. & Hänninen, H. 2011. Recovery of photosynthetic capacity in Vaccinium vitis-idaea during mild spells in winter. –Plant Ecology 212:1429–1440. DOI 10.1007/s11258-011-9918-y
Lundell, R., Saarinen, T., & Hänninen, H. 2010. Effects of snowmelt on the springtime photosynthesis of the evergreen dwarf shrub Vaccinium vitis-idaea. –Plant Ecology & Diversity 2:121-130. DOI: 10.1080/17550874.2010.497195
Saarinen, T. & Lundell, R.2010. Overwintering of Vaccinium vitis-idaea in two subarctic microhabitats - a reciprocal transplantation experiment. –Polar Research 29:38–45. DOI: doi.org/10.1111/j.1751-8369.2010.00152.x
Lundell, R. Saarinen, T., Åström, H. & Hänninen, H.2008. The boreal dwarf shrub Vaccinium vitis-idaea retains its capacity for photosynthesis throughout winter. – Botany 86:491-500. DOI: doi.org/10.1139/B08-022