Problems in the stomatal resistance measurement on Capsicum annuum

Determination of stomatal diffusion resistance by commercially available porometers can give results affected by variability, the model of instrument used and calibration. Two types of porometers, i. e. transit time and steady state are used in plant physiology studies and so a comparison between the results of the two types seemed interesting. Experiments were carried on using a Licor 1600 steady state porometer and a Delta T transit time porometer. Two sweet pepper plots were grown: one maintained at a high soil water potential (about -0.02 MPa) and the other stressed ( -0.3 MPa). Experiments compared the two instruments, using a given technique and the effects of clamping the instrument to the leaves on the measurements made over a period of about 10 minutes. The variability of stomatal resistance at different spots on the same leaf was also investigated as was the relationship between incident photosynthetically active radiation and stomatal resistance