Document: GRE-3-30-23

Photosynthetic activity of arctic evergreens under the snow: Implications in the ecosystem carbon budget.

STARR, G.* and S.F.OBERBAUER

Florida International University, Miami, FL, 33199, USA. ¹

Abstract:
We found favorable conditions for significant physiological activity in the subnivean environment of the Alaskan arctic tundra during spring. The physical properties of the snow load during spring melt produces a natural greenhouse with elevated concentrations of CO₂ Temperatures in the subnivean environment were as much as 4 ^o C warmer and CO₂ concentrations were 30 ppm above ambient conditions. These increases in temperature and carbon dioxide coupled with increasing levels of light under the snow allow for significant photosynthetic activity in four species: Ledum palustre, Vaccinium vitis-idea, Eriophorum vaginatum, and Cassiope tetragona. Photosynthetic rates under ambient conditions were as high as 20% of growing season maxima, while measures of Amax reached approximately 40% of the growing season maxima. In addition, the average variable fluorescence, Fv/Fm, of the four species was approximately 50% of their summer maxima. At the species level, this activity although quite variable, helps compensate for large winter losses of carbon due to foliar respiration when light inputs are nonexistent. This physiological activity also enabled the plants to reach their maximum physiological capacity quickly once melt occurred. These four species comprise 30% of the vascular ground cover in the tussock tundra community, and they are significant contributors to the ecosystem carbon budget. Evidence is growing that the proportion of these species in the community is declining with recent warming trends, and that the tundra community shows increased dominance by the deciduous shrub Betula nana. In the last decade it has been shown that the Alaskan tundra has become a carbon source with the increases in annual temperature. Losses of evergreens should alter the community's carbon sink-source capacity in the spring, making the system a larger carbon source.

Keywords: Subnivean environment, evergreen photosynthesis, ecosystem carbon source-sink capacity

This abstract is being presented at: 4:45 PM in session:
Oral Session #30: Effects of Elevated Carbon Dioxide.