Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 535564
Title The functional dependence of canopy conductance on water vapor pressure deficit revisited
Author(s) Fuchs, Marcel; Stanghellini, Cecilia
Source International Journal of Biometeorology 62 (2018)7. - ISSN 0020-7128 - p. 1211 - 1220.
Department(s) PE&RC
GTB Tuinbouw Technologie
Publication type Refereed Article in a scientific journal
Publication year 2018
Keyword(s) Air humidity - Coupling - Stomata - Transpiration
Abstract Current research seeking to relate between ambient water vapor deficit (D) and foliage conductance (gF) derives a canopy conductance (gW) from measured transpiration by inverting the coupled transpiration model to yield gW = m − n ln(D) where m and n are fitting parameters. In contrast, this paper demonstrates that the relation between coupled gW and D is gW = AP/D + B, where P is the barometric pressure, A is the radiative term, and B is the convective term coefficient of the Penman-Monteith equation. A and B are functions of gF and of meteorological parameters but are mathematically independent of D. Keeping A and B constant implies constancy of gF. With these premises, the derived gW is a hyperbolic function of D resembling the logarithmic expression, in contradiction with the pre-set constancy of gF. Calculations with random inputs that ensure independence between gF and D reproduce published experimental scatter plots that display a dependence between gW and D in contradiction with the premises. For this reason, the dependence of gW on D is a computational artifact unrelated to any real effect of ambient humidity on stomatal aperture and closure. Data collected in a maize field confirm the inadequacy of the logarithmic function to quantify the relation between canopy conductance and vapor pressure deficit.
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