Articles
PARAMETER ESTIMATION AND VALIDATION OF A CANOPY PHOTOSYNTHESIS MODEL FOR KIWIFRUIT VINES
The response of leaf A to I for kiwifruit (Actinidia deliciosa) vines was described using non-rectangular hyperbola and asymptotic exponential equations.
The non-rectangular hyperbola curve approached the asymptote slowly and accordingly over-estimated the radiation-saturated rate of A (Asat). The asymptotic exponential curve fitted satisfactorily to measured rates of A at all values of I, and gave reasonable estimates of Asat and the quantum yield (
i). While the asymptotic exponential curve must be integrated numerically to describe canopy A, "3-point Gaussian" integration enables fast and simple computation of this integral.Changes with leaf ontogeny in the photosynthetic capacity were included in the canopy A model, using polynomial regressions describing the relationship between leaf age and the parameters Asat, 
and ρ. Leaf area within the canopy was partitioned into age classes (up to 7), allowing temporal variations in the irradiance response of leaf A to be considered in estimates of canopy A. Simulations with this model illustrated the disproportionately large contribution of leaf area produced early in the season to the seasonal integral of canopy A.
Validation of the simulation model of canopy A, using field measurements of A for the whole-canopy, indicated a reasonable fit of the model to the data.
Measured i at low I was higher than that simulated and afternoon depressions in measured canopy A were not predicted.
Measured canopy respiration (during darkness) exceeded simulated canopy respiration.
Differences between simulated and measured canopy A are discussed in terms of canopy form and hence light interception.