Background/Question/Methods Semiarid ecosystems are particularly interesting with respect to biogeochemical cycling; the key abiotic variables controlling biogeochemical pools and processes (carbon and nitrogen storage, NPP, and nutrient exchange dynamics) are water availability and temperature, as they vary in time and space, and soil texture as it varies across landscapes. Nitrogen availability is of lesser, but still significant, importance, where humans have altered it. We hypothesize that net primary productivity and ecosystem respiration respond differently to precipitation, temperature, and N availability changes in time and space. Two fundamental tenets of our hypothesis are that net primary productivity responds more to precipitation (soil water) than temperature, and that heterotrophic respiration responds more rapidly to environmental change than autotrophic processes (NPP and autotrophic respiration). Results/Conclusions We will present a conceptual model that summarizes the potential effects of increased temperature, increased and decreased precipitation, and changes in N availability on the storage of C and N in semiarid ecosystems, on both short and long time scales.