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Calculating Air Leakage Rates in Controlled‐Environment Chambers Containing Plants
Author(s) -
Acock B.,
Acock M. C.
Publication year - 1989
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/agronj1989.00021962008100040014x
Subject(s) - leakage (economics) , chemistry , respiration , carbon dioxide , respiration rate , analytical chemistry (journal) , environmental science , botany , environmental chemistry , biology , macroeconomics , organic chemistry , economics
Air leakage rates from semi‐closed plant growth chambers under elevated CO 2 concentration ([CO 2 ]) treatments must be known in order to calculate plant CO 2 exchange (CE). It is usually assumed that air leakage rates cannot be measured with plants in the chambers, so air leakage rates are measured before and after each experiment, and assumed to remain constant or vary linearly over time. Variability in leakage rate will diminish the accuracy of calculating CE. A method for calculating air leakage rate at night in the presence of respiring plants was devised. Simultaneous equations for three situations were developed: (i) when respired CO 2 = CO 2 leaked from chamber; (ii) when [CO 2 ] is maintained at a set level overnight by injection; and (iii) when respired CO 2 > CO 2 leaked from chamber. All equations were based on two principles: (i) at night, the change in mass of CO 2 within the chamber results from a loss of CO 2 by leakage and a gain by respiration; and (ii) leakage of CO 2 from the chamber is proportional to the difference between chamber [CO 2 ] and ambient [CO 2 ]. Respiration rate is assumed constant during the measurement period. Results are reported for the situation when chamber [CO 2 ] reaches an equilibrium overnight (respired CO 2 = CO 2 leaked). Air leakage rate was found to have a coefficient of variability as high as 26.2% over eight daily measurements. Errors in calculating CE depend on the magnitude of the leakage rate, its variability, [CO 2 ], and photosynthetic activity. A leakage rate that varied by 10% from two air changes h −1 in the 800 μL L −1 [CO 2 ] treatment chamber could have given a 5% error in calculating CE during a cloudless day and a 14% error during a day with complete cloud cover. Using these procedures, variability in leakage rate can be checked automatically each day, with plants in the chamber, and without monitoring any gas except CO 2 .