The boreal dwarf shrub Vaccinium vitis-idaea retains its capacity for photosynthesis through the winter

Abstract

The ability to retain their photosynthetic capacity through the winter may be important for plants in boreal conditions, where the growing season is relatively short and winter temperatures fluctuate from severe freezing up to near 0 °C. The snow cover is an important protector for field-layer plants against both extreme freezing and excessive light, both of which could damage the photosynthetic apparatus. To understand the importance of wintertime photosynthetic activity for evergreen boreal dwarf shrubs, the photosynthesis of Vaccinium vitis-idaea L. was monitored in field conditions for one year. A dynamic model was used to determine the relative effect of temperature on the photosynthetic capacity. Our results show that V. vitis-idaea retains its photosynthetic capacity throughout the winter: its average photosynthetic capacity in winter was almost 25% of the yearly maximum measured. Changes in photosynthetic capacity over the year reflect the changes in air temperature with a certain delay, except in summer. Concentrations of soluble sugars remained high during the winter months, probably as a consequence of CO2 uptake under the snow cover. Our measurements indicated no significant damage to the leaf tissue over the winter, but suggest that photoinhibition may occur immediately after snowmelt.

Spatial variation in CO2 exchange at a northern aapa mire

“…Mosses have a clear, species-specific moisture optimum for photosynthetic capacity (Dilks and Proctor 1979): moss photosynthesis in mires is largely controlled by surface peat moisture. The photosynthetic capacity of cold climate evergreen dwarf shrubs has been observed to show large variations, even during the growing season (Karlsson 1985;Lundell et al 2008), which could be a result of water stress during summer (Karlsson 1985) or of some other, yet unidentified, limiting factor overriding temperature during the summer months (Lundell et al 2008). Our results are, however, contrasting to several previous studies where mire communities dominated by evergreen plants have been more stable in their CO 2 dynamics (Leppälä et al 2008), as well as more resistant to drought (Bubier et al 2003;Riutta et al 2007a) than communities dominated by graminoids.…”

“…Second, the removal of the snow insulation allows the sun's radiative warming to start to melt the ice cores inside the strings. Where frost or other lack of water does not impede, evergreen plants can start photosynthetizing immediately following snow melt (Bubier et al 1998;Moore et al 2006), or even before that (Lundell et al 2008). Kingsbury and Moore (1987) proposed that string plants suffer from transpiration stress in the early growing season frost conditions.…”

Photosynthetic ecophysiology of evergreen leaves in the woody angiosperms – a review

“…However, when snow cover partly melts allowing access of sufficient light, positive net photosynthesis resumes, as in low-statured arctic evergreen shrubs Vaccinium vitis-idaea, Ledum palustre and Cassiope tetragona (Starr and Oberbauer 2003). In snow covered Vaccinium vitis-idaea photosynthetic capacity dropped to 4% of annual maximum during the coldest period but recovered to 25% of maximum before snow melt (Lundell et al 2008). Also Rhododendron ferrugineum retained substantial photosynthetic capacity under a heavy snowpack (Larcher and Siegwolf 1985).…”

Cold Season Physiology of Arctic Plants

“…Arctic tundra vegetation has been shown to be photosynthetically ready during the winter-spring transition (Oberbauer et al 1996), and evidence published a decade ago provided evidence of photosynthetic activity under the snow (Lundell et al 2008;Lundell et al 2010). It has yet to be determined how these evergreens manage their water balance over the winter and acquire the water required to sustain photosynthesis during snowmelt.…”

“…As snow begins to melt in the spring, a process that may take a week or more, water percolates from the upper snow layers down to the snow-soil interface where it might be available to plant roots. During cold season photosynthesis, such as that described by Starr and Oberbauer (2003) and Lundell et al (2008Lundell et al ( , 2010, plants may be transpiring, implying that the water losses are replaced or the plants undergo water deficits.…”