MODEL VALIDATION FOR ESTIMATING THE LEAF STOMATAL CONDUCTANCE IN cv.  CABERNET SAUVIGNON GRAPEVINES

Francisco Jara-Rojas¹, Samuel Ortega-Farías¹*, Héctor Valdés-Gómez^{1, 2}, Carlos Poblete¹, and Alejandro del Pozo³

ABSTRACT

The coupled model of assimilation and stomatal conductance (A-g_s) was evaluated to estimate leaf stomatal conductance of a drip-irrigated vineyard (Vitis vinifera L. cv. Cabernet Sauvignon) located in the Pencahue Valley (35º22’ S, 71°47’ W, 150 m.a.s.l.), Maule Region, Chile, during the 2003-2004 and the 2004-2005 growing seasons. Additionally, a calibration of the three parameters mesophyll conductance (g_m), maximum specific humidity (D_max) and coupled factor (f₀) was applied on vines growing in 35 L pots. An infrared gas analyzer was used to calibrate and evaluate the A-g_s which allowed simultaneous measuring of the leaf net CO₂ assimilation (A) and stomatal conductance (g_s) in 2 to 3 h intervals of time. The calibration indicated that the g_m,, D_max and f₀ values were 1.15 mm s^-1, 52.31 g kg^-1 and 0.90, respectively. The validation in the drip-irrigated vineyard indicated that the A-g_s model was able to estimate the leaf stomatal conductance with a root mean square error (RMSE) of 0.05 mol m^-2 s^-1, model efficiency of 61% and agreement index of 90%. The sensitivity analysis indicated that the A-g_s model is affected considerably by the g_m, D_max and f₀ parameterization.

Key words: A-g_s model, photosynthesis, mesophyll conductance, stem water potential, sensitivity analysis.