Effects of increased snow on growth and allocation patterns of Arctic plants

Abstract

While summer warming in the Arctic has led to an increase in shrub cover on the tundra, winter processes may enhance shrub growth. In particular, greater snow accumulation around shrub patches may alter plant growth by insulating soil and facilitating overwinter nitrogen mineralization by microbes, thereby increasing nutrients available to plants at spring thaw and influencing growth patterns. We used three snow fences located across a gradient of shrub height and density at Toolik Field Station to compare plant growth and nutrient uptake on either side of the fences. Species behaved individualistically, with some showing increased growth and nutrient uptake with snow addition, others showing decreased growth and nutrient uptake, and some showing no effect of snow. The biggest increases in growth were seen in the deciduous shrub Salix pulchra due to increased carbon allocation (compared to nitrogen allocation) to stems, coinciding with increases in secondary growth, which allowed plants to support more branches and thus more leaves. Overall, secondary growth was the most responsive growth trait to snow addition, and facilitated growth of other aboveground plant parts. This provides a preliminary mechanistic explanation for the widespread increase in shrub cover across the northern latitudes. Some species, notably the evergreen shrub Ledum palustre, showed decreased growth under snow addition, but increased nitrogen uptake in stems suggesting storage of nutrients over growth. In addition, species growing in inherently more productive areas responded most strongly to added snow, indicating that larger plants are better able to modify their biomass and nutrient allocation in response to environmental alteration. We conclude that faster-growing species with the ability to respond rapidly to changes in nutrient availability will likely dominate under continued climate change, and may alter important ecosystem processes such as carbon and nitrogen storage and potentially feed back into climate warming.