ECOCELLS - TOOLS FOR MESOCOSM SCALE MEASUREMENTS OF GAS-EXCHANGE

We describe the use of a unique plant growth facility, which has as it s centerpiece four 'EcoCELLs', or 5x7 m mesocosms designed as open-flo w, mass-balance systems for the measurement of carbon, water and trace gas fluxes. This system is unique in that it was conceived specifical ly to bridge the gap between measurement scales during long-term exper iments examining the function and development of model ecosystems. The re are several advantages to using EcoCELLs, including (i) the same th eory of operation as leaf level gas exchange systems, but with continu ous operation at a much larger scale; (ii) the ability to independentl y evaluate canopy-level and ecosystem models; (iii) simultaneous manip ulation of environmental factors and measurement of system-level respo nses, and (iv) maximum access to, and manipulation of, a large rooting volume. In addition to discussing the theory, construction and relati ve merits of EcoCELLs, we describe the calibration and use of the EcoC ELLs during a 'proof of concept' experiment, This experiment involved growing soybeans under two ambient CO2 concentrations (similar to 360 and 710 mu mol mol(-1)). During this experiment, we asked 'How accurat e is the simplest model that can be used to scale from leaf-level to c anopy-level responses?' in order to illustrate the utility of the EcoC ELLs in validating canopy-scale models.