TY - JOUR
T1 - Water Availability Impacts on Evapotranspiration Partitioning
AU - Scott, Russell L.
AU - Knowles, John F.
AU - Nelson, Jacob A.
AU - Gentine, Pierre
AU - Li, Xi
AU - Barron-Gafford, Greg
AU - Bryant, Ross
AU - Biederman, Joel A.
N1 - Funding Information:
Funding for these sites was provided by the US Department of Agriculture's Agricultural Research Service and the US Department of Energy's Office of Science. PG was funded by NASA grant #80NSSC18K0998. The grassland and woodland sites have the AmeriFlux abbreviations US-Wkg and US-CMW, respectively, and all the data for them can be found at the following repository: https://ameriflux.lbl.gov. USDA is an equal opportunity provider and employer.
Funding Information:
Funding for these sites was provided by the US Department of Agriculture's Agricultural Research Service and the US Department of Energy's Office of Science. PG was funded by NASA grant #80NSSC18K0998. The grassland and woodland sites have the AmeriFlux abbreviations US-Wkg and US-CMW, respectively, and all the data for them can be found at the following repository: https://ameriflux.lbl.gov . USDA is an equal opportunity provider and employer.
Publisher Copyright:
© 2020
PY - 2021/2/15
Y1 - 2021/2/15
N2 - Knowing how evapotranspiration (ET) is mediated by abiotic and biotic pathways is essential to understanding how water affects ecosystem productivity. Recent studies have investigated the average transpiration fraction (T/ET) across sites and biomes, but the temporal variability of the partitioning and its controls are less understood. Here, we examine how water availability may regulate the seasonal to interannual variability of ET partitioning. To do this, we leveraged four partitioning techniques and long-term (14 years) eddy-flux records from a semiarid grassland and riparian woodland site in southeastern Arizona USA that share the same climate but differ in water table depth. T/ET was sensitive to changes in water availability over space and time as evidenced by consistently lower and more variable T/ET at the grassland, where the vegetation does not access groundwater. Seasonally, a pronounced dry foresummer T/ET depression at the rainfall-dependent grassland resulted in a bimodal T/ET distribution. In contrast, T/ET was unimodally distributed at the groundwater-dependent woodland, where high T/ET levels were maintained throughout both the dry and wet summer periods. Annual transpiration at both sites closely tracked water availability as quantified by ET, whereas abiotic evaporation was nearly constant. All ET partitioning methods yielded similar patterns of seasonal and interannual T/ET, although they differed by approximately 5 to 10% in magnitude. At both sites, transpiration was most closely correlated to plant metrics (photosynthesis, leaf area index) and ET, whereas evaporation was most correlated to surface moisture variables (soil moisture, precipitation). However, substantial differences between monthly and annual correlations demonstrate variable controls on monthly partitioning throughout the year. These results provide novel insights into the effects of water availability on the seasonal and interannual variability of ET partitioning and illuminate mechanisms regulating terrestrial ecosystem carbon and water exchange.
AB - Knowing how evapotranspiration (ET) is mediated by abiotic and biotic pathways is essential to understanding how water affects ecosystem productivity. Recent studies have investigated the average transpiration fraction (T/ET) across sites and biomes, but the temporal variability of the partitioning and its controls are less understood. Here, we examine how water availability may regulate the seasonal to interannual variability of ET partitioning. To do this, we leveraged four partitioning techniques and long-term (14 years) eddy-flux records from a semiarid grassland and riparian woodland site in southeastern Arizona USA that share the same climate but differ in water table depth. T/ET was sensitive to changes in water availability over space and time as evidenced by consistently lower and more variable T/ET at the grassland, where the vegetation does not access groundwater. Seasonally, a pronounced dry foresummer T/ET depression at the rainfall-dependent grassland resulted in a bimodal T/ET distribution. In contrast, T/ET was unimodally distributed at the groundwater-dependent woodland, where high T/ET levels were maintained throughout both the dry and wet summer periods. Annual transpiration at both sites closely tracked water availability as quantified by ET, whereas abiotic evaporation was nearly constant. All ET partitioning methods yielded similar patterns of seasonal and interannual T/ET, although they differed by approximately 5 to 10% in magnitude. At both sites, transpiration was most closely correlated to plant metrics (photosynthesis, leaf area index) and ET, whereas evaporation was most correlated to surface moisture variables (soil moisture, precipitation). However, substantial differences between monthly and annual correlations demonstrate variable controls on monthly partitioning throughout the year. These results provide novel insights into the effects of water availability on the seasonal and interannual variability of ET partitioning and illuminate mechanisms regulating terrestrial ecosystem carbon and water exchange.
KW - Eddy covariance
KW - Grassland
KW - Groundwater
KW - Productivity
KW - Riparian woodland
KW - Semiarid
KW - Transpiration
KW - Water use efficiency
UR - http://www.scopus.com/inward/record.url?scp=85096861894&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85096861894&partnerID=8YFLogxK
U2 - 10.1016/j.agrformet.2020.108251
DO - 10.1016/j.agrformet.2020.108251
M3 - Article
AN - SCOPUS:85096861894
SN - 0168-1923
VL - 297
JO - Agricultural and Forest Meteorology
JF - Agricultural and Forest Meteorology
M1 - 108251
ER -