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Interactions between Carbon Dioxide and Water Deficits Affecting Leaf Photosynthesis: Simulation and Testing
Author(s) -
Grant Robert F.
Publication year - 1992
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1992.0011183x003200060003x
Subject(s) - carbon dioxide , photosynthesis , carbon fixation , irradiance , biology , horticulture , botany , atmospheric sciences , saturation (graph theory) , ecophysiology , zoology , ecology , physics , mathematics , quantum mechanics , combinatorics
Atmospheric CO 2 concentration is known to have contrasting effects on photosynthesis, particularly in C 3 plant species. These effects may be produced mathematically through the combination of a biochemically based submodel of CO 2 fixation in leaf chloroplasts with a physically based submodel of CO 2 and H 2 O diffusion through leaf surfaces and atmospheric boundary layers. Water‐deficit effects may be represented in both submodels. The behavior of a combined model was tested against data recorded under atmospheric CO 2 concentrations of 330 and 660 μmol mol −1 in the Soil—Plant—Atmosphere Research Units at the University of Florida. The model reproduced changes in the quantum requirements of CO 2 fixation and in diurnal CO 2 fluxes of soybean [ Glycine max . (L.) Merr.] leaves at these different concentrations. Simulated CO 2 fixation at midday responded more to increased CO 2 concentration at high irradiance (22.9 vs. 42.0 μmol m −2 s −1 at 1050 μmol m −2 s −1 ) than at low (17.1 vs. 19.7 μmol m −2 s −1 at 330 μmol m −2 s −1 ), as found experimentally. Under water deficits (leaf water potential ψ l = −1.55 MPa), light saturation of CO 2 fixation occurred at lower irradiance, again consistent with experimental findings. Interaction between the water deficit effects in each submodel allowed the combined model to simulate a higher sensitivity of CO 2 fixation at 660 μmol mol −1 (41.1 vs. 19.3 μmol m −2 s −1 ) than at 330 (22.9 vs. 14.2 μmol m −2 s −1 ) when ψ l was reduced to −1.55n from −0.60 MPa, as observed experimentally. The theoretical basis for CO 2 effects on photosynthesis is well established, allowing them to be reproduced with confidence in the absence of water deficits. However, the theoretical basis for water deficit effects on photosynthesis is incomplete, such that the reproduction of CO 2 effects on photosynthesis in the presence of water deficits must still be regarded as speculative.