Characterization of resource heterogeneity in space (patches) and time (pulses) at scales of days to weeks and decimeters to meters will be undertaken. In addition to chemical and physical measures of resource heterogeneity, assessments of how this resource variability is perceived by plants will be pursued, including: Root and foliage characteristics that reflect local resource availability, acquisition of resources, competition with other plants and microbes for resources, and translation of resources gleaned from patches and pulses into fitness and seedling recruitment. Plant response to incongruity of resources and factors that might smoothe heterogeneity (mycorrhizae and water efflux from roots) will also be investigated. Parameters to be measured include nutrient pools, flux rates through nitrogen pools, microbial biomass, soil water potential, plant nutrient acquisition, photosynthesis, root uptake kinetics, respiration and growth, and biomass and seed production. Stable isotopes will feature prominently in the work including new isotopic dilution procedures. Data collected in addressing 21 hypotheses will also be applied in a new modeling application of Ecological Field Theory and kriging interpolation. The study features two species each of shrubs, perennial grasses and exotic annual grasses. The current conversion of the sagebrush steppe from a perennial system to exotic annuals is also addressed. This research will produce findings of importance to the general ecology and ecosystem function of arid lands as well as to the management of grazing land resources.
