From leaf to crop : quantifying photosynthesis responses of two flower crops
Variations in environment factors, e.g., light intensity, light spectrum, water and nutrient level, and crop structure manipulations may occur in the greenhouse. Changes in these factors could affect ornamental crop production in the greenhouse through affecting plant photosynthesis at different levels, e.g., leaf, plant and crop level. The aim of this thesis was to quantify photosynthesis responses to (i) combined changes in photosynthetically active radiation (PAR) and red to far-red ratio
... to far-red ratio (R:FR), (ii) water and nitrogen stress combinations and (iii) crop structure manipulations at different levels for two ornamental crops: lily and rose. Using the photosynthesis model of Farquhar, von Caemmerer and Berry (the FvCB model) and the stomatal conductance model of Ball, Woodrow and Berry (the BWB model), leaf photosynthesis responses to water and nitrogen stress combinations were quantified for lily. The changes of the FvCB model parameters due to variations of water and nitrogen conditions were linearly correlated with the changes of leaf nitrogen per unit leaf area. Most of the BWB model parameters did not depend on the nitrogen level. Using a functional-structural plant model, photosynthesis responses to changes in PAR and R:FR, and the presence of bent shoots were quantified at plant and crop level for rose. At mild shade, plant responses to low R:FR were more important for plant photosynthesis, while with the increase of shade level, plant responses to low PAR became more important. Moreover, the consequences of responses to changes in PAR and R:FR for plant photosynthesis tended to mitigate each other. The presence of bent shoots increased flower shoots dry weight, which was entirely due to the contribution of extra photosynthesis by bent shoots. In addition, bent shoots reflected relatively more farred than red light, which lowered the R:FR in light reflected upwards that can be received by flower shoots. The low R:FR from below was associated with a steeper leaf angle in flower shoots, which increased canopy photosynthesis by allowing more light to penetrate to the lower plant parts. Overall this thesis illustrates the importance of considering the interactions of multiple factors when quantifying photosynthesis responses to environmental variations. A functionalstructural plant model is a useful tool to upscale photosynthesis responses from leaf to crop level.