Original articleValidation of a Photosynthesis Model through the Use of the CO2Balance of a Greenhouse Tomato Canopy

Several leaf photosynthesis models were developed from well controlled experiments in growth chambers. However, only a few have been validated under greenhouse conditions for their quantitative and qualitative adequacy. In this paper, rates of net photosynthesis for a tomato crop (Lycopersicon esculentum Mill) were measured in a semi-commercial greenhouse (615 m3) for a significant time period. Concomitant measurements of climatic conditions and LAI were used for simulation of net photosynthesis using the TOMGRO model which integrates Acock's model for photosynthesis calculations. From simulations and from sensitivity analysis, the prediction of net photosynthesis appeared to be very sensitive to the quantum use efficiency. The Acock model with original parameters underestimated the net photosynthesis rate, but an increase in the quantum use efficiency by 10% gave a good fit. In an effort to generalize the validity of the model, a residual analysis was performed and showed a systematic bias related to light intensity intercepted by the canopy. The Marquardt algorithm was used to adjust our data to the model but did not eliminate residual heterogeneity of variance with new parameter values. On the basis of collected data, the criteria of goodness of fit used showed that the photosynthesis model is inadequate in describing the CO2-balance of the greenhouse agrosystem. However, it was determined that it could be used as a submodel within a more complex model for predicting growth and development.