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Association between sap flow‐derived and eddy covariance‐derived measurements of forest canopy CO 2 uptake
Author(s) -
Klein Tamir,
Rotenberg Eyal,
Tatarinov Fyodor,
Yakir Dan
Publication year - 2016
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.13597
Subject(s) - eddy covariance , canopy , environmental science , atmospheric sciences , transpiration , ecosystem respiration , primary production , carbon sink , flux (metallurgy) , carbon cycle , tree canopy , ecosystem , ecology , botany , photosynthesis , chemistry , biology , organic chemistry , geology
Summary The carbon sink intensity of the biosphere depends on the balance between gross primary productivity ( GPP ) of forest canopies and ecosystem respiration. GPP , however, cannot be directly measured and estimates are not well constrained. A new approach relying on canopy transpiration flux measured as sap flow, and water‐use efficiency inferred from carbon isotope analysis ( GPP SF ) has been proposed, but not tested against eddy covariance‐based estimates ( GPP EC ). Here we take advantage of parallel measurements using the two approaches at a semi‐arid pine forest site to compare the GPP SF and GPP EC estimates on diurnal to annual timescales. GPP SF captured the seasonal dynamics of GPP EC ( GPP SF = 0.99 × GPP EC , r 2 = 0.78, RMSE = 0.82, n = 457 d) with good agreement at the annual timescale (653 vs 670 g C m −2 yr −1 ). Both methods showed that GPP ranged between 1 and 8 g C m −2 d −1 , and the GPP SF / GPP EC ratio was between 0.5 and 2.0 during 82% of the days. Carbon uptake dynamics at the individual tree scale conformed with leaf scale rates of net assimilation. GPP SF can produce robust estimations of tree‐ and canopy‐scale rates of CO 2 uptake, providing constraints and greatly extending current GPP EC estimations.