CO ₂ exchange and evapotranspiration across dryland ecosystems of southwestern North America

Journal Article · Wed Apr 19 00:00:00 EDT 2017 · Global Change Biology

DOI:https://doi.org/10.1111/gcb.13686· OSTI ID:1389140

Biederman, Joel A. ^[1]; Scott, Russell L. ^[1]; Bell, Tom W. ^[2]; Bowling, David R. ^[3]; Dore, Sabina ^[4]; Garatuza‐Payan, Jaime ^[5]; Kolb, Thomas E. ^[4]; Krishnan, Praveena ^[6]; Krofcheck, Dan J. ^[7]; Litvak, Marcy E. ^[7]; Maurer, Gregory E. ^[7]; Meyers, Tilden P. ^[6]; Oechel, Walter C. ^[8]; Papuga, Shirley A. ^[9]; Ponce‐Campos, Guillermo E. ^[1]; Rodriguez, Julio C. ^[10]; Smith, William K. ^[9]; Vargas, Rodrigo ^[11]; Watts, Christopher J. ^[12]; Yepez, Enrico A. ^[5] ; Goulden, Michael L. ^[13]

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1. Southwest Watershed Research Center Agricultural Research Service Tucson AZ USA
2. Earth Research Institute University of California Santa Barbara Santa Barbara CA USA
3. Department of Biology University of Utah Salt Lake City UT USA
4. School of Forestry Merriam‐Powell Center for Environmental Research Northern Arizona University Flagstaff AZ USA
5. Departamento de Ciencias del Agua y Medio Ambiente Instituto Tecnológico de Sonora Ciudad Obregón Sonora Mexico
6. Atmospheric Turbulence and Diffusion Division Air Resources Laboratory National Oceanographic and Atmospheric Administration Oak Ridge TN USA
7. Department of Biology University of New Mexico Albuquerque NM USA
8. Global Change Research Group Department of Biology San Diego State University San Diego CA USA, Department of Geography College of Life and Environmental Sciences Exeter UK
9. School of Natural Resources and the Environment University of Arizona Tucson AZ USA
10. Departamento de Agricultura y Ganaderia Universidad de Sonora Hermosillo Sonora Mexico
11. Department of Plant and Soil Sciences University of Delaware Newark DE USA
12. Departamento de Fisica Universidad de Sonora Hermosillo Sonora Mexico
13. Department of Earth System Science University of California Irvine Irvine CA USA

Abstract

Global‐scale studies suggest that dryland ecosystems dominate an increasing trend in the magnitude and interannual variability of the land CO ₂ sink. However, such analyses are poorly constrained by measured CO ₂ 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 gC m ⁻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 (R _eco ) 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 R _eco 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 CO ₂ exchange may be up to 3–5 times larger than current estimates.

• Sponsoring Organization: USDOE
• OSTI ID: 1389140
• Journal Information: Global Change Biology, Journal Name: Global Change Biology Journal Issue: 10 Vol. 23; ISSN 1354-1013
• Publisher: Wiley-Blackwell
• Country of Publication: United Kingdom
• Language: English