Automated closed-system canopy-chamber for continuous field-crop monitoring of CO2 and H2O fluxes

An automated transient-state closed-system canopy-chamber for gas-exchange determinations of field-crops was developed to allow unattended day and night, high frequency CO2 and H2O exchange measurements, with short measurement time (15 s) and high scanning rate (0.5 s). Environment tests on the chamber performance indicated that: atmospheric pressure variation during operation was 10-20 Pa and limited to a few seconds; leaks introduced maximum errors of 1% in the flux calculation; turbulence effect on CO2 and H2O fluxes was not detectable; during the measurement period, temperature build-up inside the chamber was typically within 1-2 degreesC range; photosynthetic photon flux density (RP) attenuation by the chamber as a whole was in the 15-20% range; whereas, net radiation (R) inside the chamber was always higher than outside by 10-20%. The flux determinations of the automated canopy-chamber were compared with other methods. Daily evapotranspiration (E) of artichoke obtained by canopy-chamber was at the most 4.2% lower than E obtained by high-precision weighing lysimeter. Diurnal E and carbon exchange rates (A) of sugarbeet and marjoram crops obtained by canopy-chamber closely followed the pattern of those obtained by the Bowen-ratio/energy-balance (BREB) method, with maximum daily underestimations of 6-8 and 5-6% for E and A, respectively. No differences in flux calculations came out when the rate of change in CO2 and H2O concentrations was derived either by linear or quadratic regressions (QR). The results of all tests and comparisons showed that the automated chamber presented is a valuable and accurate tool for monitoring day and night CO2 and H2O fluxes. (C) 2002 Elsevier Science B.V. All rights reserved.