Climate impacts on carbon cycling in drylands: What we know and what we don't

Sasha Reed, Armin Howell, Cara Lauria and Robin Reibold, Southwest Biological Science Center, U.S. Geological Survey, Moab, UT, Joel A. Biederman, Southwest Watershed Research Center, USDA-ARS, Tucson, AZ, Ryan T. Choi, Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT, Natasha MacBean, Geography, Indiana University, Bloomington, IN, Brooke B. Osborne, US Geological Survey, Moab, UT, Michala Phillips, Botany and Plant Sciences, University of California Riverside, Riverside, CA, Benjamin Poulter, Biospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, William Smith, School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, Colin Tucker, Northern Research Station, US Forest Service, Madison, WI, Daniel E. Winkler, Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA

Background/Question/Methods
Together hyperarid, arid, semiarid, and subhumid ecosystems (hereafter drylands) represent our planet’s largest terrestrial biome, making up over 40% of the land surface and driving the interannual variability and trend in Earth’s terrestrial carbon sink. Drylands also have been shown to respond rapidly and non-linearly to climate change, with important implications for carbon cycling and climate at the global scale, yet our understanding of the dryland carbon cycle and of how global changes will affect this cycle remains poor relative to other biomes. At the same time, key aspects of dryland carbon cycling are distinct from other ecosystem types. For example, drylands host large expanses of photosynthetic soil (i.e., biocrusts), enormous stocks of inorganic soil carbon, and variable CO2 fluxes that are sometimes difficult to resolve with low per-unit-area organic carbon storage. In this talk, we will bring together diverse dryland carbon cycling data – including those from remote sensing, eddy co-variance towers, atmospheric measurements, automated soil CO2assessment, modeling, and long-term in situ climate manipulation experiments – to assemble a contemporary understanding of dryland carbon cycling and response to change.
Results/Conclusions
We will use a range of data, tools, and perspectives to explore the dryland carbon cycle and the types, drivers, and outcomes of change in these ecosystems. Topics will include dryland controls over and amounts of CO2 exchanged with the atmosphere, the storage of carbon in organic and inorganic forms, carbon cycling phenology, climate effects on photosynthesis and respiration, and climate-induced changes to plant communities that affect carbon storage and cycling, as well as challenges and opportunities associated with dryland remote sensing, automated CO2 measurement, and modeling. Further, although water is clearly a central control over dryland carbon cycling and change, we will also consider the role of multiple interacting resources (e.g., nutrient availability) in determining how carbon moves among and is stored within drylands, both now and into the future. Drylands are warming and drying more quickly than the global mean and the increased frequency and severity of droughts, deluges, and temperatures sub-optimal for biota translate into sensitive systems that are crossing thresholds. This talk will investigate the mechanisms behind and consequences of current and expected changes to drylands in the context of global biogeochemistry and climate.