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Keywords:

  • Ball-Berry-Leuning;
  • canopy processes;
  • hydrologic modeling;
  • parameterization;
  • stomatal conductance;
  • water flux

Abstract

[1] Stomatal conductance (gs) models are widely used at a variety of scales to predict fluxes of mass and energy between vegetation and the atmosphere. Several gs models contain a parameter that specifies the minimum gs estimate (g0). Sensitivity analyses with a canopy flux model (MAESTRA) identified g0 to have the greatest influence on transpiration estimates (seasonal mean of 40%). A spatial analysis revealed the influence of g0 to vary (30–80%) with the amount of light absorbed by the foliage and to increase in importance as absorbed light decreased. The parameter g0 is typically estimated by extrapolating the linear regression fit between observed gs and net photosynthesis (An). However, our measurements demonstrate that the gs-An relationship may become nonlinear at low light levels and thus, extrapolating values from data collected over a range of light conditions resulted in an underestimation of g0 in Malus domestica when compared to measured values (20.4 vs 49.7 mmol m−2 s−1 respectively). In addition, extrapolation resulted in negative g0 values for three other woody species. We assert that g0 can be measured directly with diffusion porometers (as gs when An ≤ 0), reducing both the time required to characterize g0 and the potential error from statistical approximation. Incorporating measured g0 into MAESTRA significantly improved transpiration predictions versus extrapolated values (6% overestimation versus 45% underestimation respectively), demonstrating the benefit in gs models. Diffusion porometer measurements offer a viable means to quantify the g0 parameter, circumventing errors associated with linear extrapolation of the gs-An relationship.