Sagebrush steppe is a widespread ecosystem in western North America, and provides many ecological services such as carbon and water storage, maintenance of soil health, and habitat for threatened species such as sage grouse, black-tailed prairie dog and pygmy rabbits. In arid ecosystems, photosynthesis is tightly coupled with water, energy, and biochemical processes. In particular, deep-rooted shrubs are ecosystem engineers in these systems, and strongly shape water redistribution and fluxes at leaf to landscape scales. Artemisia spp. shrubs occur across large gradients in elevation (300 m to 2400m), temperature (0°C to 22°C MAT), and precipitation (100 mm to 1000 mm per year). Despite the extensive occurrence of this locally abundant shrub, our understanding of the water relations of these shrubs and their communities is limited. Accurate estimates of plant water use are essential for predicting changes in water storage and cycling associated with forecasted environmental challenges in the sagebrush steppe ecosystem. We quantified water transport and use (hydraulic conductivity, sap flow, transpiration) and status (water potential) at different organizational scales (leaf and branch) in two widespread subspecies of basin big sagebrush (Artemisia tridentata ssp. wyomingensis and A. t. ssp. vaseyana) at Reynolds Creek Critical Zone Observatory, in Southwestern Idaho.
Results/Conclusions
We observed differences in the seasonal patterns and amount of water storage and transport in these sagebrush subspecies. Both daily leaf-level transpiration and daily leaf-specific sap flux were consistently greater in A. t. ssp. vaseyana compared to A. t. ssp. wyomingensis throughout the growing season, especially in early summer. Mid-day and predawn water potentials were more negative (by -1 MPa to -2.5 MPa) in A. t. ssp. wyomingensis compared to A. t. ssp. vaseyana the growing season. Leaf-specific hydraulic conductivity was greater in A. t. ssp. wyomingensis compared to A. t. ssp. vaseyana, a known drought-tolerance strategy for reducing tension in the xylem. Greater transpiration in A. t. ssp. vaseyana could be due to greater water availability, as indicated by greater (less negative) water potentials. Overall, our findings show that water loss at both leaf and branch scales is greater in A. t. ssp. vaseyana, which could be due to morphological and physiological differences between the sub-species, or due to site differences. A. t. ssp. vaseyana occupies wetter and cooler sites compared to A. t. ssp. wyomingensis. Quantifying differences in water transport and use among sub-species is vital for accurate modelling of ecosystem water storage and cycling in sagebrush steppe.