Open AccessSap flux–upscaled canopy transpiration, stomatal conductance, and water use efficiency in an old growth forest in the Great Lakes region of the United States
Author(s) -
Tang Jianwu,
Bolstad Paul V.,
Ewers Brent E.,
Desai Ankur R.,
Davis Kenneth J.,
Carey Eileen V.
Publication year - 2006
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2005jg000083
Subject(s) - transpiration , eddy covariance , canopy , canopy conductance , environmental science , stomatal conductance , vapour pressure deficit , photosynthetically active radiation , evapotranspiration , atmospheric sciences , tree canopy , flux (metallurgy) , aceraceae , hydrology (agriculture) , botany , maple , ecology , ecosystem , biology , chemistry , photosynthesis , geology , geotechnical engineering , organic chemistry
Combining sap flux and eddy covariance measurements provides a means to study plant stomatal conductance and the relationship between transpiration and photosynthesis. We measured sap flux using Granier‐type sensors in a northern hardwood‐dominated old growth forest in Michigan, upscaled to canopy transpiration, and calculated canopy conductance. We also measured carbon and water fluxes with the eddy covariance method and derived daytime gross primary production (GPP). The diurnal patterns of sap flux and canopy transpiration were mainly controlled by vapor pressure deficit ( D ) and photosynthetically active radiation (PAR). Daily sums of sap flux and canopy transpiration had exponential relationships to D that saturated at higher D and had linear relationships to PAR. Sugar maple ( Acer saccharum ) and yellow birch ( Betula alleghaniesis ) had higher sap flux per unit of sapwood area than eastern hemlock ( Tsuga canadensis ), while sugar maple and hemlock had higher canopy transpiration per unit of leaf area than yellow birch. Sugar maple dominated canopy transpiration per ground area. Canopy transpiration averaged 1.57 mm d −1 , accounting for 65% of total evapotranspiration in the growing season. Canopy conductance was controlled by both D and PAR, but the day‐to‐day variation in canopy conductance mainly followed a negatively logarithmic relationship with D . By removing the influences of PAR, half‐hourly canopy conductance was also negatively logarithmically correlated with D . Water use efficiency (WUE) had a strong exponential relationship with D on a daily basis and approached a minimum of 4.4 mg g −1 . WUE provides an alternative to estimate GPP from measurements of sap flux.