Ability of multiplicative models to simulate stomatal resistance along plant growth: application to New Guinea impatiens grown in a greenhouse

Abstract : In greenhouses, optimized plant crop management is crucial for environmental reasons and for maintaining the competitiveness of the horticultural sector. In particular, optimizing water consumption is of high interest but requires predictive models needing leaf stomatal resistance Rs estimation. Until now, most studies deduced Rs by inverting the energy balance equation. On contrary, the objective of the present study is to model Rs for leaves on the entire height of the canopy from direct measurements with a porometer. The model was first established and validated for the upper leaves and then tested for the within-canopy leaves. In this prospect, New Guinea Impatiens plants were cultivated in containers inside a greenhouse during 16 weeks under water-comfort irrigation management. Global radiation, temperature and relative humidity of the air were continuously recorded while the stomatal resistance was measured at the top and in the middle of the canopy. Two models involving global radiation and vapor pressure deficit (Jarvis multiplicative models) were tested by using two parameterization methods. The first method consisted in deducing the model parameters independently for each week. Results showed significant differences between the parameters and a generic model could not be obtained. In the second method the model parameters were obtained from a subset of experimental data. Validating the model on the remaining datasets was quite conclusive. By extrapolating the obtained model from the upper leaves to the middle canopy leaves using the Beer-Lambert law to estimate the global radiation, acceptable correlations were reached between estimated and measured Rs. Results were however not as good as those obtained for the upper leaves.