RCCZO -- Soil Biogeochemistry, Stable Isotopes, Vegetation -- Plant & Soil Isotopes and Climate -- Reynolds Creek Experimental Watershed -- (2015-2015)

The overarching goal of this study is to better understand the relationship between plant carbon (C) and nitrogen (N) isotopic signatures and climate in a sagebrush-steppe ecosystem. Additionally, this study seeks to a) determine how plant isotopic data in the sampled ecosystem compare with global patterns with respect to broader climate gradients; and b) evaluate any additional effects on plant isotopic compositions due to soil attributes (chemical, physical). Climatic effects on C and N isotopes were analyzed by examining plant and soil samples across a climatic gradient within the Reynolds Creek Critical Zone Observatory (RCCZO) (comprised of the USDA ARS Reynolds Creek Experimental Watershed) located in the Owyhee Mountains in southwestern Idaho. Sampling focused on two subwatersheds (Johnston Draw and Whiskey Hills) in July 2015. Soil cores were obtained from both plant and interplant spaces, with a total of 480 samples (120 cores at 4 depth intervals). Samples of plants (n=120) present at each core location were collected at the same time soils were obtained to allow for evaluating relationships between soil and plant processes. At each plant location, samples consist of sagebrush foliar tissue, while samples from interplant plots often consisted of a mixture of grasses and forbs. Soil data include soil moisture, gravimetric water content, soil organic matter, stable carbon and nitrogen isotopes, percent carbon and nitrogen, initial/final/potential nitrate concentration, initial/final/potential ammonium concentration, net nitrification rate, potential net nitrification rate, net mineralization rate, potential net mineralization rate, and pH. Note: the majority of extractions for ammonium concentrations were contaminated so ammonium (and thus mineralization) data is largely unavailable for this study. Plant data includes stable carbon and nitrogen isotopes and percent carbon and nitrogen for sagebrush foliar tissues (perennial leaves only).