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ISHS Acta Horticulturae 654: International Workshop on Models for Plant Growth and Control of Product Quality in Horticultural Production

EVALUATION OF CROP PHOTOSYNTHESIS MODELS FOR DYNAMIC CLIMATE CONTROL

Author:   O. Krner
Keywords:   climate regime, energy saving, greenhouse, simulation, stomata resistance
Abstract:
Within dynamic climate regimes reliable crop photosynthesis models are needed to optimise the relationship between CO2 supply and crop photosynthesis. In those regimes stomata resistance (rs) can increase when temperature rises and this influences photosynthesis. In models, however, rs is often considered constant, while it is known to vary with greenhouse climate. In this paper, a biochemical based leaf photosynthesis model was combined with a simple rs model for crops and implemented in a crop gross photosynthesis (Pgc) model. Pgc models with fixed (80 m s-1) and simulated rs were compared to each other as well as to measured CO2 crop gas exchange at different temperatures and CO2 levels (23C, 28C, 33C; 400, 700, 1000 μmol mol-1 CO2). Measured data were fitted to the negative exponential light response curve and Pgc was predicted for different light levels (300, 600, 900, 1200 μmol m-2 s-1 PPFD). The rs module did not influence Pgc prediction at temperatures around 23C. Measured Pgc was well predicted by both models. Pgc was overestimated at 33C when rs was assumed fixed. Within measurements, temperature that maximised Pgc was below 23C with 400 μmol mol-1 CO2 at all tested PPFD levels, but increased from 400 to 1000 μmol mol-1 CO2 with at least 1C, 3.5C and 4.5C at 600, 900 and 1200 μmol m-2 s-1 PPFD, respectively. The model predictions were sufficient at PPFD ≥900 μmol m-2 s-1 when the rs model was used (<1C difference to the measurements), but overestimated the measurements when rs was constant (>2C difference). No model was the best at all climate conditions in simulating actual crop photosynthesis, but simulating rs within a Pgc model showed a good effect when predicting temperature that maximises crop photosynthesis.
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