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CO 2 exchange and evapotranspiration across dryland ecosystems of southwestern North America
Author(s) -
Biederman Joel A.,
Scott Russell L.,
Bell Tom W.,
Bowling David R.,
Dore Sabina,
GaratuzaPayan Jaime,
Kolb Thomas E.,
Krishnan Praveena,
Krofcheck Dan J.,
Litvak Marcy E.,
Maurer Gregory E.,
Meyers Tilden P.,
Oechel Walter C.,
Papuga Shirley A.,
PonceCampos Guillermo E.,
Rodriguez Julio C.,
Smith William K.,
Vargas Rodrigo,
Watts Christopher J.,
Yepez Enrico A.,
Goulden Michael L.
Publication year - 2017
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.13686
Subject(s) - eddy covariance , evapotranspiration , environmental science , ecosystem , ecosystem respiration , primary production , sink (geography) , carbon sink , atmospheric sciences , hydrology (agriculture) , precipitation , terrestrial ecosystem , ecology , geography , geology , meteorology , cartography , geotechnical engineering , biology
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.