Global-scale studies suggest that dryland ecosystems dominate an increasing trend in the magnitude and interannual variability of the land CO2 sink. However, such analyses are poorly constrained by measured CO2 exchange in drylands. Here we address this observation gap with eddy covariance data from 25 sites in the water-limited Southwest region of North America with observed ranges in annual precipitation of 100–1000 mm, annual temperatures of 2–25°C, and records of 3–10 years (150 site-years in total). Annual fluxes were integrated using site-specific ecohydrologic years to group precipitation with resulting ecosystem exchanges. We found a wide range of carbon sink/source function, with mean annual net ecosystem production (NEP) varying from -350 to +330 gCm−2 across sites with diverse vegetation types, contrasting with the more constant sink typically measured in mesic ecosystems. In this region, only forest-dominated sites were consistent carbon sinks. Interannual variability of NEP, gross ecosystem production (GEP), and ecosystem respiration (Reco) was larger than for mesic regions, and half the sites switched between functioning as C sinks/C sources in wet/dry years. The sites demonstrated coherent responses of GEP and NEP to anomalies in annual evapotranspiration (ET), used here as a proxy for annually available water after hydrologic losses. Notably, GEP and Reco were negatively related to temperature, both interannually within site and spatially across sites, in contrast to positive temperature effects commonly reported for mesic ecosystems. Models based on MODIS satellite observations matched the cross-site spatial pattern in mean annual GEP but consistently underestimated mean annual ET by ~50%. Importantly, the MODIS-based models captured only 20–30% of interannual variation magnitude. These results suggest the contribution of this dryland region to variability of regional to global CO2 exchange may be up to 3–5 times larger than current estimates. Published 2017. This article is a U.S. Government work and is in the public domain in the USA
资助项目:
Biederman, J.A.
; Southwest Watershed Research Center, Agricultural Research ServiceUnited States
; 电子邮件: joel.biederman@ars.usda.gov
Southwest Watershed Research Center, Agricultural Research Service, Tucson, AZ, United States; Earth Research Institute, University of California Santa Barbara, Santa Barbara, CA, United States; Department of Biology, University of Utah, Salt Lake City, UT, United States; School of Forestry, Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ, United States; Departamento de Ciencias del Agua y Medio Ambiente, Instituto Tecnológico de Sonora, Ciudad Obregón, Sonora, Mexico; Atmospheric Turbulence and Diffusion Division, Air Resources Laboratory, National Oceanographic and Atmospheric Administration, Oak Ridge, TN, United States; Department of Biology, University of New Mexico, Albuquerque, NM, United States; Global Change Research Group, Department of Biology, San Diego State University, San Diego, CA, United States; Department of Geography, College of Life and Environmental Sciences, Exeter, United Kingdom; School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, United States; Departamento de Agricultura y Ganaderia, Universidad de Sonora, Hermosillo, Sonora, Mexico; Department of Plant and Soil Sciences, University of Delaware, Newark, DE, United States; Departamento de Fisica, Universidad de Sonora, Hermosillo, Sonora, Mexico; Department of Earth System Science, University of California Irvine, Irvine, CA, United States
Recommended Citation:
Biederman J.A.,Scott R.L.,Bell T.W.,et al. CO2 exchange and evapotranspiration across dryland ecosystems of southwestern North America[J]. Global Change Biology,2017-01-01,23(10)