Soil and leaf CNP&S stoichiometry and isotopic composition in sagebrush ecosystems of Wyoming

Sagebrush (Artemisia tridentata) ecosystems span a wide range of environmental conditions in the Western US, where they are the most extensive semiarid vegetation type. Water availability is recognized as the major driver of the structure of sagebrush communities, however less is known about the associated biogeochemical processes. By characterizing large-scale biogeographical patterns of carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) elemental and isotopic compositions in soil and vegetation, we aimed to: (1) detect potential nutrient limitations, (2) identify element sources (weathering, decomposition, or atmospheric deposition), and (3) identify the nature and rates of biogeochemical processes. We sampled sagebrush leaves together with intra- and inter-canopy soil at 50 sites across Wyoming, where sagebrush extends across strong climate and soil type gradients. We expect the nature, rates, and coupling of biogeochemical processes to correlate with patterns of water availability since it is a key control of microbial activity, and the diffusion of enzymes and substrates. Nutrient availability for plants may also follow the same pattern. For example, in moist sites, increased N and P availability may result from higher organic matter decomposition rates than in dry sites, potentially alleviating N limitation to plant growth. However, an excess of P relative to N may occur at high decomposition rates and where the soil parent material is P-rich, leaving N as the limiting nutrient. Conversely, warm and dry sites may have a greater proportion of N being lost through fractionating pathways and a more open N cycle, resulting in high soil and foliar d15N values. We expect leaf d34S to reflect contrasting sources, notably helping to decipher the relative importance of the inputs from atmospheric deposition and weathering (i.e. sedimentary material deposited under anoxic conditions). By improving our understanding of the biogeochemical processes associated with vegetation productivity patterns along a macro-climatic gradient, our data could provide insights into future ecosystem status and help designing disturbance recovery strategies.