A Null Balance Carbon Dioxide and Water Vapour Porometer

Abstract

The Binos IRGA is suitable for portable use in the field after modification and can be added to the null-balance water vapour diffusion porometer in a closed loop with the porometer chamber and used as a null-balance indicator for measurements of CO² flux, without the need for substantial structural or electrical modification. The null-balance concept works satisfactorily in the measurement of both CO² influx and efflux and enables the CO² flux to be measured at either the ambient CO² concentration or at other known CO² concentrations. The combined CO² and water vapour porometer enables measurements of the rate of photosynthesis, and estimates of stomatal and mesophyll conductance to be made extensively in the field without the need for an elaborate mobile laboratory.