Early Spring Nitrogen Uptake by Snow-Covered Plants: A Comparison of Arctic and Alpine Plant Function under the Snowpack

We compared nitrogen (N) acquisition by alpine and arctic tundra plants during snowmelt, and assessed its significance relative to season-long N demand. We then related plant responses in alpine and arctic tundra to soil and air temperature. Parallel experiments were conducted in an alpine moist meadow at Niwot Ridge, Colorado, and in arctic dry heath and moist tussock tundra near Toolik Lake, Alaska. We added 99%-enriched 15NH415NO3 (0.5 g N m−2) to the snowpack, and traced the fate of the 15N into plants and soil by harvesting samples before snowmelt ended. All alpine and arctic plants acquired N during snowmelt. However, alpine plants acquired 100 times more N than arctic plants. Using data from published studies, we estimated season-long N demand for the vascular plant species. In the alpine tundra, N uptake during snowmelt constituted over 12% of season-long uptake for a graminoid species, and averaged 7.4% for perennial forbs. In contrast, N uptake during snowmelt by arctic plants averaged less than 0.1% of season-long N uptake. Soil temperatures were similar in these systems during snowmelt, averaging −0.4°C in the arctic and −0.5°C in the alpine tundra. However, arctic plants experienced lower winter soil temperatures than alpine plants. Winter soil surface temperatures averaged −7.75°C in arctic and −2.43°C in alpine tundra systems, and the lowest weekly mean temperature was −14.5°C in the arctic and −6.14°C in the alpine systems. Thus, differences in plant N uptake are likely due to winter conditions, rather than conditions that occurred during uptake. In conclusion, plant acquisition of N resources during snowmelt is important in alpine systems.