HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Acock, B. Articles by Acock, M. C. Search for Related Content PubMed Articles by Acock, B. Articles by Acock, M. C. Agricola Articles by Acock, B. Articles by Acock, M. C.

Calculating Air Leakage Rates in Controlled-Environment Chambers Containing Plants

USDA/ARS Systems Res. Lab., Natural Resources Inst., BARC-W, Beltsville, MD 20705

^* Corresponding author.

Air leakage rates from semi-closed plant growth chambers under elevated C0₂ concentration ([CO₂]) treatments must be known in order to calculate plant CO₂ 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 C0₂ = CO₂ leaked from chamber; (ii) when [CO₂] is maintained at a set level overnight by injection; and (iii) when respired CO₂ > CO₂ leaked from chamber. All equations were based on two principles: (i) at night, the change in mass of C0₂ within the chamber results from a loss of C0₂ by leakage and a gain by respiration; and (ii) leakage of CO₂ from the chamber is proportional to the difference between chamber [CO₂] and ambient [CO₂]. Respiration rate is assumed constant during the measurement period. Results are reported for the situation when chamber [CO₂] reaches an equilibrium overnight (respired C0₂ = CO₂ 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, [CO₂], and photosynthetic activity. A leakage rate that varied by 10% from two air changes h^–1 in the 800 µL L^–1 [CO₂] 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 CO₂.

Received for publication August 15, 1988.

This article has been cited by other articles:

				D. Timlin, D. Fleisher, S.-H. Kim, V. Reddy, and J. Baker Evapotranspiration Measurement in Controlled Environment Chambers: A Comparison between Time Domain Reflectometry and Accumulation of Condensate from Cooling Coils Agron. J., January 1, 2007; 99(1): 166 - 173. [Abstract] [Full Text] [PDF]