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Crop Net Carbon Dioxide Exchange Rate and Radiation Use Efficiency in Soybean
Author(s) -
Rochette Philippe,
Desjardins Raymond L.,
Pattey Elizabeth,
Lessard Robert
Publication year - 1995
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1995.00021962008700010005x
Subject(s) - photosynthetically active radiation , leaf area index , photosynthesis , canopy , environmental science , carbon dioxide , agronomy , growing season , atmospheric sciences , chemistry , botany , biology , organic chemistry , geology
Abstract Plant growth is directly related to the fraction of the C fixed by photosynthesis that is converted into phytomass. We report here the results of a study aiming at the estimation of the net CO 2 exchange rates (CNCER) of a soybean crop over the growing season. Hourly values of CNCER were estimated based on eddy correlation measurements of CO 2 fluxes above the canopy, on chamber measurements of CO 2 fluxes at the soil surface, and on the assumption that root respiration can be computed as a fraction of plant daily photosynthesis. Mean daytime CNCER varied between 0.70 and 0.83 mg m −2 s −1 for a leaf area index (LAI) greater than 1, with a maximum hourly value of 1.48 mg m −2 s −1 . Absolute mean nighttime CNCER values were usually <20% of daytime values. Hourly CNCER varied nonlinearly with intercepted photosynthetically active radiation (IPAR). The accuracy of the CNCER estimates was evaluated by comparing the radiation use efficiency of the soybean crop calculated using CNCER estimates with radiation use efficiency calculated using phytomass accumulation. Agreement between the two approaches was within 10% for LAI>2, but calculated CNCER overestimated radiation use efficiency based on phytomass accumulation for smaller values of LAI.