Evolution of the composition isotopic of the continuum soil-plant-atmosphere

Journal Article · Thu Feb 01 04:00:00 EST 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90330-N· OSTI ID:6935754

Bariac, T; Jusserand, C; Mariotti, A ^[1]

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1. Universite Pierre et Marie Curie, Paris (France)

Intensive daily sampling of the soil-plant-atmosphere continuum was carried out to determine the vertical evolution of diurnal variation of the isotopic composition of (1) water in leaves from a maize canopy at the experimental site of Villeau, Eure et Loir (France) and (ii) water vapor in the atmosphere above and within the canopy. Applying some reasonable assumptions, the isotopic model of the transpiration process (I.M.T.) fits well the daily enrichment cycle of {sup 18}O and {sup 2}H in the leaf water sampled at different levels of the plants. The most important factors influencing the variations of {sup 18}O and {sup 2}H content are the relative humidity of the air and the kinetic enrichment factor occurring during transpiration. The discrepancies between the measured and the calculated values seem to be closely related to the differences between the isotopic composition of the water pools in the leaf. Without experimental data on the transpiration flux and the root water uptake, the I.M.T. allows a relatively precise determination of the nature (transient or stationary) of the isotopic state of the water in the leaf. When {delta}{sup 18}O and {delta}{sup 2}H present steady-state values, the water fluxes are always conservative in the transpiring pools of the leaf. When the heterogeneity of the pools of the leaf is taken into account, it appears that the leaf does not present systematically an instantaneous isotopic steady-state. The results reported here indicate that the assumption of the constancy of {epsilon}{sub k} values is invalid: the discrepancy in {epsilon}{sub k} values between the leaves at the top of the canopy and the other ones can be related to the increase of the turbulence of the atmosphere with height in the canopy.

• OSTI ID: 6935754
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:2; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
AIR-BIOSPHERE INTERACTIONS
BIOGEOCHEMISTRY
BIOLOGICAL ACCUMULATION
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EUROPE
EVEN-EVEN NUCLEI
FLUIDS
FRANCE
GASES
GEOCHEMISTRY
HYDROGEN ISOTOPES
ISOTOPE RATIO
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LIGHT NUCLEI
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ODD-ODD NUCLEI
OXYGEN 18
OXYGEN ISOTOPES
PLANTS
SEASONAL VARIATIONS
STABLE ISOTOPES
TRANSPIRATION
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WATER VAPOR
WESTERN EUROPE