Sagebrush steppe is a widespread ecosystem in western North America, covering about 4.5 x 106 ha of total land area. This ecosystem has been identified as a potential carbon (C) sink. The greater sagebrush steppe ecosystems of the Intermountain West consist of many species and subspecies of sagebrush (Artemisia spp.). It covers a wide geographical range with distinct climatic conditions ranging from rain- to snow-dominated environments. With changing climatic conditions, the distribution and associated ecosystem functions of this ecosystem are expected to shift. However, it is hard to predict how the ability of these ecosystems to sequester C in the future will change without basic knowledge of the C balance (C gain vs C loss) of these systems today. Previous studies have found phenological, morphological, and ecophysiological differences among sagebrush subspecies, any or all of which may influence the overall C balance. We conducted a field study to quantify both daily and seasonal C fluxes at different organizational scales (leaf, plant, ecosystem) in two widespread subspecies of basin big sagebrush (Artemisia tridentata ssp. wyomingensis and A. t. ssp. vaseyana) at Reynolds Creek Critical Zone Observatory (RC-CZO), in Southwestern Idaho, at a rain-dominated and snow-dominated site, respectively. We conducted diel measurements of leaf-level CO2 fluxes (photosynthesis, A) and ecosystem-scale CO2 fluxes (net ecosystem exchange, NEE) monthly May-August, 2016.
Results/Conclusions
We observed differences in both the patterns and magnitude of A and NEE at diel scales. Both A and NEE values were consistently greater in A. t. ssp. vaseyana at the snow-dominated site compared to A. t. ssp. wyomingensis at the rain-dominated site, irrespective of the time of the day. Cumulative-seasonal A and NEE were also significantly greater at the snow-dominated site (52.60 g CO2/m2-leaf /d) compared to rain-dominated site (46.45 g CO2/m2-leaf/d). Similarly, cumulative NEE values were also almost 2X greater in A. t. ssp. vaseyana (32.97 g CO2/m2-ground/d) compared to A. t. ssp. wyomingensis (14.29 g CO2/m2-ground/d). A and NEE were greatest in June, and minimal during August, in both sagebrush communities. Overall, our findings show that CO2-uptake is greater in A. t. ssp. vaseyana compared to A. t. ssp. wyomingensis at multiple spatial and time scales, and these differences are important for C modeling.