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A Compensating Method for Measuring Carbon Dioxide Exchange, Transpiration, and Diffusive Resistance of Plants under Controlled Environmental Conditions
Author(s) -
Bazzaz F. A.,
Boyer J. S.
Publication year - 1972
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1934091
Subject(s) - transpiration , carbon dioxide , photosynthesis , respiration , relative humidity , boundary layer , light intensity , chemistry , environmental science , atmospheric sciences , botany , thermodynamics , biology , physics , organic chemistry , optics
A semi—closed compensating system is described for measuring CO 2 exchange and transpiration simultaneously under controlled environmental conditions. The compensating feature permits conditions in the assimilation chamber to be kept uniform and within narrow limits. Temperature, relative humidity, carbon dioxide concentration, wind speed, and light intensity may be varied within the system. Since transpiration and photosynthesis can be measured simultaneously, diffusive resistances to carbon dioxide and water transport may also be calculated from the data. The performance of the apparatus was checked with Ambrosia trifida L. Net photosynthesis occurred at a rate of 32 mg hr — 1 dm — 2 of leaf area and 30°C under saturating light intensities, and transpiration took place at 5.3 gm hr — 1 dm — 2 under the same conditions. Both processes were sensitive to CO 2 concentrations from 100 to 400 ppm and the temperatures between 15° and 30°C. Respiration was relatively insensitive to temperature below 20°C. Although the response time of the instrument was only a few seconds, net photosynthesis and dark respiration did not reach steady rates until 45—60 min after the lights were turned on or off. Diffusive resistance to CO 2 transport were 0.08, 0.8, and 5.2 sec cm — 1 for the boundary layer of the leaf, internal gas phase of the leaf, and the mesophyll cells, respectively. Diffuse resistances to water transport were 0.05 and 0.5 sec cm — 1 for the boundary layer and internal gas phase of the leaf, respectively.