Design and performance of a portable gas exchange chamber system for CO 2- and H 2O-flux measurements in crop canopies

Abstract

There is unsatisfactory information on CO 2- and H 2O-fluxes at the canopy scale of crop plants and the possible effects of climate and management factors and on these fluxes. The design and performance of a portable open chamber system to measure canopy CO 2- and H 2O-fluxes under field conditions is described here. The performance of the chamber system was tested in a crop rotation of sugar beet and winter wheat and the main climatic driving forces for CO 2- and H 2O-fluxes were determined. Measured fluxes were also validated using data from destructive growth analysis and calculation of reference evapotranspiration according to FAO-guidelines. Chamber walls reduced total incident radiation by 19% and increased the fraction of diffuse radiation. Maximum temperature increase inside the chamber was less than 5 °C, and rarely exceeded 2 °C after canopy closure. Canopy CO 2 exchange rates (CCER) and evapotranspiration ( E C) closely tracked transitional changes of radiation and potential evaporation, respectively. Daily carbon gain of wheat calculated from canopy CO 2 exchange data was very similar to that from destructive harvests while for sugar beet flux measurements slightly underestimated above ground biomass production. E C measured with chambers was only slightly lower than calculated reference evapotranspiration. The canopy gas exchange system presented here is a suitable experimental approach to assess interactions of environmental and management factors and canopy gas exchange properties.