ISHS Acta Horticulturae 313: III International Symposium on Computer Modelling in Fruit Research and Orchard Management
PARAMETER ESTIMATION AND VALIDATION OF A CANOPY PHOTOSYNTHESIS MODEL FOR KIWIFRUIT VINES |
| Authors: | J.G. Buwalda, J.S. Meekings |
| Keywords: | irradiance, asymptotic exponential function, spatial integration, temporal variation |
| Abstract:
Canopy photosynthesis (A) models, central components of carbon balance models, are frequently based on empirical descriptions of the irradiance (I) response of leaf A spatially integrated for the canopy. 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, 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 | |
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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.
