Photosynthetic and phenological responses of dwarf shrubs to the depth and properties of snow

Abstract

Snow is known to have a major impact on vegetation in arctic ecosystems, but little is known about how snow affects plants in boreal forests, where the snowpack is uneven due to canopy impact. The responses of two dwarf shrubs, the evergreen Vaccinium vitis‐idaea and the deciduous V. myrtillus, to snow conditions were studied in a snow manipulation experiment in southern Finland. The thermal insulation of the snowpack was expected to decrease with partial removal or compression of the snow, while addition of snow was expected to have the opposite effect. The penetration of light was manipulated by partial removal of snow or by formation of an artificial ice layer in the snowpack. CO2 exchange measurements that were carried out at the time of maximum snow depth in late March indicated significant photosynthetic activity in the leaves of V. vitis‐idaea under snow. Net gain of CO2 was observed in the daytime on all the manipulation plots, excluding the snow addition plots, where light intensity was very low. The subnivean photosynthesis compensated for a substantial proportion (up to 80%) of the respiratory CO2 losses. Chlorophyll fluorescence measurements indicated reduced potential capacity of photosystem II in the leaves of V. vitis‐idaea on those plots where snow cover was thin. Neither V. vitis‐idaea nor V. myrtillus suffered from frost damage (assessed as electrolyte leakage) when thermal insulation was reduced by means of snow manipulations. No phenological responses were observed in V. vitis‐idaea, but in V. myrtillus bud burst, leaf unfolding and flowering were advanced by 1–3 days on the addition plots. The results of the present study show that dwarf shrubs respond to not only the thickness of snow but also the physical properties of snow, both of which are expected to change due to climatic warming.

Short‐term climate change manipulation effects do not scale up to long‐term legacies: effects of an absent snow cover on boreal forest plants

“…The two most common dwarf shrubs of the understorey, V. myrtillus and V. vitis-idaea, showed abundant discoloration of leaf and stem tissue and partly reduced growth, especially in the short-term treatment. Both discoloration and growth reduction are common signs of frost damage in woody plants (Sakai & Larcher 1987;Gu et al 2008) and have previously been observed in these species if exposed to an earlier snowmelt or insufficient snow depth (Raatikainen & V€ anninen 1988;Wipf 2009;Gerdol et al 2013;Wheeler et al 2014;Saarinen et al 2015). We generally found V. myrtillus to be more sensitive than V. vitis-idaea.…”

“…As such, snow is a critical regulator of understorey vegetation health and composition (Rasmus, Lundell & Saarinen ; Kreyling, Haei & Laudon ; Saarinen et al . ) as well as soil processes, and a lack of snow has been shown to alter carbon and nutrient fluxes into the next growing season (Groffman et al . ,b, , ; Olsson & Falkengren‐Grerup ; Öquist & Laudon ; Haei et al .…”

“…This reduction in snow cover can lead to the phenomenon of 'colder soils in a warmer world' (Groffman et al 2001a), as less insulation during winter increases soil freezing and the frequency of soil freeze-thaw cycles. As such, snow is a critical regulator of understorey vegetation health and composition (Rasmus, Lundell & Saarinen 2011;Kreyling, Haei & Laudon 2012;Saarinen et al 2015) as well as soil processes, and a lack of snow has been shown to alter carbon and nutrient fluxes into the next growing season (Groffman et al 2001a(Groffman et al ,b, 2006(Groffman et al , 2011Olsson & Falkengren-Grerup 2003;€ Oquist & Laudon 2008;Haei et al 2013;Campbell, Socci & Templer 2014). Plant responses, particularly root responses, are suggested drivers of these changes, but remain far less studied than biogeochemical soil alterations (but see Tierney et al 2001;Comerford et al 2013;Campbell, Socci & Templer 2014).…”

The importance of snow in species distribution models of arctic vegetation

“…Many observational and experimental studies have highlighted the regulative role of snow in multiple biological functions and ecological properties: e.g. vegetative biomass and growth (Choler 2015), vascular plant species richness and assemblages (Odland andMunkejord 2008, Carlson et al 2015), soil microbial activity and composition (Schimel et al 2004, Zinger et al 2009), overwintering survival (Rapacz et al 2014), root dynamics and mortality (Templer 2012), and photosynthetic capacity (Saarinen et al 2016).…”

Morphological characteristics and photosynthetic capacity of Fragaria vesca L. winter and summer leaves

“…When low freezing temperatures occur or the leaves are covered by deep snow, the actual rates of CO 2 assimilation are probably low (Saarinen et al, 2015). However, our previous results show that the evergreen dwarf shrub Vaccinium vitis-idaea can attain a net gain in carbon during the winter months (Lundell et al, 2008), and the species is able to up-regulate its photosynthesis rapidly during a mild spell (Saarinen et al, 2011).…”