Development of a simplified plant stomatal resistance model and its validation for potentially transpiring and water-stressed water hyacinths

Abstract

A simple model of upper-canopy plant stomatal resistance ( r uC ) was developed which requires but four input parameters: canopy aerodynamic resistance, upper-canopy foliage temperature, and air vapor pressure deficit and temperature. The model was tested against upper-canopy sunlit leaf stomatal resistance ( r l ) measurements of both potentially and non-potentially transpiring water hyacinth plants over the upper-canopy-intercepted net radiation range of 300–450 W m −2 and over a 10-fold range of r l . In all instances, and indicative of the model's good performance, the ratio of r uC r l consistently averaged about 1.25, due to partial self-shading of the upper-canopy foliage. The significance of this finding to air pollution studies arises from the facts that 1. (1) contemporary knowledge of a plant canopy's leaf area index would allow the transformation of r uC to r C , the total canopy diffusive resistance, and 2. (2) the proper accounting for different trace gas diffusivities would allow the transformation of r c for water vapor to the variety of r C values required to infer the gaseous deposition of important pollutant gas species at vegetated surfaces.