Snowfall, snow depth, and melt impacts on carbon cycling at the Great Basin Desert and Sierra Nevada ecotone

Climate model scenarios are highly uncertain regarding future snow depth and snow melt patterns. Snowfall provides the majority of annual soil water recharge in many western high-elevation North American ecosystems. This study examined linkages between snow depth, soil water content, physiological performance, growth, and carbon cycling for deeply-rooted shrubs at the ecotone between the Great Basin Desert and Sierra Nevada. Snow depth was manipulated using eight long-term snow fences near Mammoth Lakes, California. We compared physical and biological characteristics in response to depth (“+ snow”,” –snow”, and “ambient” depth treatments) from 2003 to 2006. Snow depth on +snow plots was about twice that of ambient-depth plots, and about 2.2 times of that for -snow plots in all years. Soils at 50 cm depth were wetter on +snow compared to ambient and –snow plots. Plant water potential was significantly affected by snow depth for the co-dominant shrub species Artemisia tridentata and Purshia tridentata. Leaf-level CO₂ and water vapor fluxes were different on +snow vs. –snow plots, but dependent upon snowfall in the prior winter. Net Primary Productivity (NPP) for A. tridentata was higher than for P. tridentata. NPP was lowest on –snow plots for A. tridentata, and highest on +snow plots for P. tridentata. Although standing biomass was higher for the two main grass species (Carex and Achnatherum spp.) across snow depth treatments, NPP was not different due to differences in plant basal area. There were significant differences in root biomass, NO₃^- , K⁺, and organic C in soils from open microsites between shrubs compared to soil under the canopies of A. tridentata and P. tridentata, and across ambient, +snow, and –snow plots. Results across years are consistent with a snow depth threshold, above which there are no increases in plant productivity, C input, and nutrient cycling for this snow-dominated ecosystem.