Biophysical controls on carbon and water vapor fluxes across a grassland climatic gradient in the United States

Pradeep Wagle, Xiangming Xiao, Russell L. Scott, Thomas E Kolb, David R. Cook, Nathaniel Brunsell, Dennis D. Baldocchi, Jeffrey Basara, Roser Matamala, Yuting Zhou, Rajen Bajgain

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

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<sup>-1</sup>ET) 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.

Original languageEnglish (US)
Pages (from-to)293-305
Number of pages13
JournalAgricultural and Forest Meteorology
Volume214-215
DOIs
StatePublished - Dec 15 2015

Fingerprint

water vapor
grasslands
grassland
carbon
vegetation index
spatial variation
global carbon budget
atmosphere
moderate resolution imaging spectroradiometer
carbon budget
eddy covariance
vapor pressure
water use efficiency
meteorological data
water balance
biosphere
MODIS
temporal variation
water budget
air temperature

Keywords

  • Ecosystem water use efficiency
  • Eddy covariance
  • Enhanced vegetation index
  • Evapotranspiration
  • Grasslands
  • Gross primary production

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Forestry
  • Atmospheric Science
  • Global and Planetary Change

Cite this

Biophysical controls on carbon and water vapor fluxes across a grassland climatic gradient in the United States. / Wagle, Pradeep; Xiao, Xiangming; Scott, Russell L.; Kolb, Thomas E; Cook, David R.; Brunsell, Nathaniel; Baldocchi, Dennis D.; Basara, Jeffrey; Matamala, Roser; Zhou, Yuting; Bajgain, Rajen.

In: Agricultural and Forest Meteorology, Vol. 214-215, 15.12.2015, p. 293-305.

Research output: Contribution to journalArticle

Wagle, P, Xiao, X, Scott, RL, Kolb, TE, Cook, DR, Brunsell, N, Baldocchi, DD, Basara, J, Matamala, R, Zhou, Y & Bajgain, R 2015, 'Biophysical controls on carbon and water vapor fluxes across a grassland climatic gradient in the United States', Agricultural and Forest Meteorology, vol. 214-215, pp. 293-305. https://doi.org/10.1016/j.agrformet.2015.08.265
Wagle, Pradeep ; Xiao, Xiangming ; Scott, Russell L. ; Kolb, Thomas E ; Cook, David R. ; Brunsell, Nathaniel ; Baldocchi, Dennis D. ; Basara, Jeffrey ; Matamala, Roser ; Zhou, Yuting ; Bajgain, Rajen. / Biophysical controls on carbon and water vapor fluxes across a grassland climatic gradient in the United States. In: Agricultural and Forest Meteorology. 2015 ; Vol. 214-215. pp. 293-305.
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AU - Cook, David R.

AU - Brunsell, Nathaniel

AU - Baldocchi, Dennis D.

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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.

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