TY - JOUR
T1 - Biophysical controls on carbon and water vapor fluxes across a grassland climatic gradient in the United States
AU - Wagle, Pradeep
AU - Xiao, Xiangming
AU - Scott, Russell L.
AU - Kolb, Thomas E.
AU - Cook, David R.
AU - Brunsell, Nathaniel
AU - Baldocchi, Dennis D.
AU - Basara, Jeffrey
AU - Matamala, Roser
AU - Zhou, Yuting
AU - Bajgain, Rajen
N1 - Funding Information:
This study was supported in part by a research grant (Project No. 2012-02355 ) through the USDA National Institute for Food and Agriculture (NIFA)’s Agriculture and Food Research Initiative (AFRI) , Regional Approaches for Adaptation to and Mitigation of Climate Variability and Change, and a research grant ( IIA-1301789 ) from the National Science Foundation EPSCoR . This research was supported by grants to T. Kolb and Northern Arizona University from the North American Carbon Program / USDA CREES NRI ( 2004-35111-15057 and 2008-35101-19076 ) and Science Foundation Arizona ( CAA 0-203-08 ). The Konza Prairie site was supported by grants to N. Brunsell from the NSF EPSCoR (NSF EPS-0553722 and EPS-0919443 ) and KAN0061396 / KAN0066263 and the NSF Long Term Ecological Research Program at Konza Prairie Biological Station ( DEB-0823341 and sub-contract: SS1093). It was also partly supported by NOAA Climate Program Office's Sectoral Applications Research Program (SARP) grant NA130AR4310122 . The Fermi site was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science Program under contract DE-AC02-06CH11357 . Funding for the Kendall and Santa Rite flux sites was from the USDA and U.S. Department of Energy's Office of Science . Data were obtained from AmeriFlux database ( http://ameriflux.ornl.gov/ ). The authors thank an anonymous reviewer for the comments on previous version of this manuscript.
Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2015/12/15
Y1 - 2015/12/15
N2 - Understanding of the underlying causes of spatial variation in exchange of carbon and water vapor fluxes between grasslands and the atmosphere is crucial for accurate estimates of regional and global carbon and water budgets, and for predicting the impact of climate change on biosphere-atmosphere feedbacks of grasslands. We used ground-based eddy flux and meteorological data, and the Moderate Resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index (EVI) from 12 grasslands across the United States to examine the spatial variability in carbon and water vapor fluxes and to evaluate the biophysical controls on the spatial patterns of fluxes. Precipitation was strongly associated with spatial and temporal variability in carbon and water vapor fluxes and vegetation productivity. Grasslands with annual average precipitation <600mm generally had neutral annual carbon balance or emitted small amount of carbon to the atmosphere. Despite strong coupling between gross primary production (GPP) and evapotranspiration (ET) across study sites, GPP showed larger spatial variation than ET, and EVI had a greater effect on GPP than on ET. Consequently, large spatial variation in ecosystem water use efficiency (EWUE=annual GPP/ET; varying from 0.67±0.55 to 2.52±0.52gCmm-1ET) was observed. Greater reduction in GPP than ET at high air temperature and vapor pressure deficit caused a reduction in EWUE in dry years, indicating a response which is opposite than what has been reported for forests. Our results show that spatial and temporal variations in ecosystem carbon uptake, ET, and water use efficiency of grasslands were strongly associated with canopy greenness and coverage, as indicated by EVI.
AB - Understanding of the underlying causes of spatial variation in exchange of carbon and water vapor fluxes between grasslands and the atmosphere is crucial for accurate estimates of regional and global carbon and water budgets, and for predicting the impact of climate change on biosphere-atmosphere feedbacks of grasslands. We used ground-based eddy flux and meteorological data, and the Moderate Resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index (EVI) from 12 grasslands across the United States to examine the spatial variability in carbon and water vapor fluxes and to evaluate the biophysical controls on the spatial patterns of fluxes. Precipitation was strongly associated with spatial and temporal variability in carbon and water vapor fluxes and vegetation productivity. Grasslands with annual average precipitation <600mm generally had neutral annual carbon balance or emitted small amount of carbon to the atmosphere. Despite strong coupling between gross primary production (GPP) and evapotranspiration (ET) across study sites, GPP showed larger spatial variation than ET, and EVI had a greater effect on GPP than on ET. Consequently, large spatial variation in ecosystem water use efficiency (EWUE=annual GPP/ET; varying from 0.67±0.55 to 2.52±0.52gCmm-1ET) was observed. Greater reduction in GPP than ET at high air temperature and vapor pressure deficit caused a reduction in EWUE in dry years, indicating a response which is opposite than what has been reported for forests. Our results show that spatial and temporal variations in ecosystem carbon uptake, ET, and water use efficiency of grasslands were strongly associated with canopy greenness and coverage, as indicated by EVI.
KW - Ecosystem water use efficiency
KW - Eddy covariance
KW - Enhanced vegetation index
KW - Evapotranspiration
KW - Grasslands
KW - Gross primary production
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U2 - 10.1016/j.agrformet.2015.08.265
DO - 10.1016/j.agrformet.2015.08.265
M3 - Article
AN - SCOPUS:84940951687
SN - 0168-1923
VL - 214-215
SP - 293
EP - 305
JO - Agricultural and Forest Meteorology
JF - Agricultural and Forest Meteorology
ER -