Dryland ecosystems make up over 40% of Earth’s terrestrial surface and a range of emerging data suggest that dryland responses to global change will help determine terrestrial responses at the global scale. At the same time, our understanding of drylands and their controls lags behind that of other systems and drylands commonly show non-linear responses to change that are not effectively captured by the conceptual models developed for these more mesic ecosystems. By definition, drylands are limited by water and past research has focused heavily on how the amount and timing of precipitation affects the structure and function of these xeric systems. This focus on water has provided critical insight into dryland function, however, has also left a gap in our understanding of how the nitrogen (N) cycle helps determine the composition, structure, and function of dryland communities. These uncertainties, in turn, constrain our capacity to forecast how a changing dryland N cycle (e.g., via increased N deposition or climate change) will affect drylands and their contribution to Earth’s biogeochemical cycles.
Results/Conclusions
Here, we present data from a series of dryland manipulation experiments, including altered climate and N deposition manipulations, to explore how vascular plants, microbial communities, biological soil crusts, and their N cycles respond to varied environmental changes. We used a N cycle lens to explore how multiple resources interact to determine dryland function and how environmental change affects drylands via effects on N pool and fluxes. We show that some drylands, although receiving low inputs of N and maintaining low N stocks, behave like N saturated systems, and we evaluate the downstream consequences of these responses (e.g., greenhouse gas emissions and air and water quality effects). We also explore patterns showing that, in some cases, water availability alone explains a surprisingly low proportion of the range of variability in dryland carbon fluxes. By including N and other biogeochemical cycles into our assessment, we are given much more explanatory power. In sum, we synthesized results from a range of experiments that began with independent questions, but which together offer an exciting picture of how the N cycle determines how drylands function and respond to change.