A null-balance diffusion porometer suitable for use with leaves of many shapes.
Abstract
Describes the theory, construction and calibration of a new type of diffusion porometer in which the leaf is placed inside the porometer chamber; it is suitable for measuring stomatal resistance [rs ] in complex, non-planar leaves. To eliminate some of the difficulties normally occurring in calibration of the humidity sensor, a null-balance system was developed in which a constant r.h. is maintained in the porometer chamber during measurement. In field trials in a Picea sitchensis forest in Scotland, in 1971, rs was found to be highest in the lowest layers of the canopy and lowest in the uppermost layers. On sunny days rs in the lower layers of the canopy was higher than on cloudy days.