Modelling stomatal conductance of wheat: An assessment of response relationships under elevated CO2

This study proposes Jarvis-type model parameterisations for estimating stomatal conductance (gs) in wheat (Triticum aestivum L.) under ambient [CO2] (a[CO2], approximately 390 μmol mol−1) and elevated [CO2] (e[CO2], approximately 550 μmol mol−1), based on measurements collected in the Australian Grains Free Air CO2 Enrichment (AGFACE) facility. Relationships of gs with phenological and environmental factors were evaluated using a boundary line technique. Results suggest that gs-response functions for vapour pressure deficit (VPD), volumetric soil moisture (VSM) and temperature dependence were different between a[CO2] and e[CO2]: VPD induced stomatal closure at approximately 3 and 2.5 kPa under a[CO2] and e[CO2] respectively, and optimum temperature was 2 °C lower under e[CO2]. Elevated [CO2] decreased maximum gs (gmax) by approximately 35%.