Effects of Diminished Seasonal Snow Cover On Nutrient Cycling.

Climate change in sagebrush-steppe ecosystems is likely to cause warmer winter temperatures and reduce winter snow cover. We have a poor understanding of how these changes will affect biochemical cycling. This project examines the relationship between diminishing snowpack and the cycling of nitrogen, phosphorus, and changes in microbial biomass, all essential to the functioning of plants and healthy soils. We expect that plots without snowpack during the winter months will have increased frequency of freeze-thaw cycles because of reduced insulation and greater exposure to fluctuating air temperatures. More freeze-thaw cycles will contribute to a release of nitrogen and phosphorus from soils and microbial biomass because disruption of soil aggregates will release nutrients and microbial mortality will lower immobilization rates. We conducted a field experiment in a semi-arid Sagebrush-Steppe ecosystem to address the possibility of increased nutrient release due to the increased freeze-thaw cycles that might result from thinner snowpacks. We used infrared heat lamps to create eight replicates each of three heating regimes; warming (lamps continuously on during the winter), snowmelt (lamps only on following snowfall), and a control (lamps always off). Plant growth was increased by warming and snowmelt treatments; however, no significance difference was found in nitrate, ammonium, or phosphorus pool sizes and net N mineralization over the winter months. These results suggest that initial increases in plant growth due to warming and reduced snowpack treatments are not due to increased nitrogen availability.