Influence of canopy structure on light interception and productivity of greenhouse cucumber
Final Report Abstract
Greenhouse cucumber (Cucumis sativus L.) production systems are characterized by a near-to-optimal level of control and supply of environmental factors like temperature, CO2, water and nutrients. However, due to the spatial inhomogeneity in these canopies the interception of light is often suboptimal for productivity. The aim was to obtain a better quantitative understanding of this limitation. Dynamical plant models are an appropriate tool, as they incorporate morphological and physiological adaptations of plants to their environment, whereas a precise simulation of the light distribution on organ level is essential to account for the interactions. In the first instance, a static three-dimensional (3D) plant model was combined with a mock-up of the surrounding canopy and a 3D radiosity based light distribution model. The results showed that simulations of leaf level photosynthetically active radiation (PAR) were suitable to derive light-induced physiological responses on organ level. To analyze yield formation, L-Cucumber, a functional-structural plant model (FSPM) of greenhouse cucumber, was extended with detailed models of leaf photosynthesis and fruit dry matter partitioning. L-Cucumber provided the possibility to account for spatial gradients of environmental factors induced by the spatial structure of the plant and the canopy, which are necessary for an accurate estimation of yield formation. In greenhouse cucumber growth imbalances between individual fruits are common. These imbalances can be related to differences in fruit growth duration until reaching harvest size, and fruit abortion. For both traits, environmental factors as well as canopy architecture play a key role for their differentiation. Introducing dominance and abortion events into the assimilate partitioning of L-Cucumber allowed simulating the typical fruit growth traits of cucumber fruits. In conclusion, the current implementation of L-Cucumber served well as a tool to analyze the impact of canopy architecture and environmental factors on productivity for cucumber greenhouse production. During the first project phase, adaptations of the original concept revealed necessary. The modelling of the diffuse light in the radiation transfer model was originally proposed to be based on Monsi & Saeki’s approach with parameters for leaf area index, leaf reflection and transmission. The lack of accounting for lateral diffuse radiation gave rise to pursue an alternative approach. During the second project phase we successfully employed the nested radiosity approach as implemented in the interface Caribu, for the L-Studio software. Caribu was developed to model the light environment of virtual plants on the organ level.
Publications
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2006. A method to analyse the radiation transfer within a greenhouse cucumber canopy (Cucumis sativus L.) Acta Horticulturae, 718: 75-80
Wiechers D, Kahlen K, Stützel H
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2008. Modelling leaf phototropism in a cucumber canopy, Functional Plant Biology, 35: 876-884
Kahlen K, Wiechers D, Stützel H
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2011. Evaluation of a radiosity based light model for greenhouse cucumber canopies. Agricultural and Forest Meteorology
Wiechers D, Kahlen K, Stützel H
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2011. Modelling photo-modulated internode elongation in growing glasshouse cucumber canopies. New Phytologist, 190: 697-708
Kahlen K, Stützel H
