Based on the results, maintaining biochemical capacity of the middle-lower canopy and increasing the leaf area of the upper canopy would be promising strategies to improve canopy photosynthesis in a high-wire cucumber cropping system. Further analyses using the approach described in this study can be expected to provide insights into the influences of horticultural practices on canopy photosynthesis and the design of optimal crop canopies.
Leaf phototropism might have significant effects on the light interception, dry matter production and yield of cucumber (Cucumis sativus L.). The objective of the present study was to model the phototropism of leaves in a greenhouse cucumber canopy. The dynamic structural model of cucumber using a parametric L-system was extended to mimic the leaf movement induced by gradients in the local light environment of each leaf. The red to far-red (R : FR) ratio is known to be a driving force in shade avoidance reactions of plants. In the model, R : FR ratios on the left and right leaf half of each individual leaf lamina were calculated and the change in tropism angle per phyllochron was based on the R : FR gradient across the leaf halves. The tropism angle of a leaf describes the deviation of the present leaf azimuth from the initial leaf orientation, which is predefined by the phyllotaxis of the plant. Even in its simple form, the model simulated photo-morphogenic canopy responses.
Dominance and abortion events need to be considered when simulating typical fruit growth traits. By integrating environmental factors, the FSPM can be a valuable tool to analyse and improve existing knowledge about the dynamics of assimilates partitioning.
One-dimensional light models using the Beer-Lambert equation (BL) with the light extinction coefficient k are simple and robust tools for estimating light interception of homogeneous canopies. Functional-structural plant models (FSPMs) are powerful to capture light-plant interactions in heterogeneous canopies, but they are also more complex due to explicit descriptions of three-dimensional plant architecture and light models. For choosing an appropriate modelling approach, the trade-offs between simplicity and accuracy need to be considered when canopies with spatial heterogeneity are concerned. We compared two light modelling approaches, one following BL and another using ray tracing (RT), based on a framework of a dynamic FSPM of greenhouse cucumber. Resolutions of hourly-step (HS) and daily-step (DS) were applied to simulate light interception, leaf-level photosynthetic acclimation and plant-level dry matter production over growth periods of two to five weeks. Results showed that BL-HS was comparable to RT-HS in predicting shoot dry matter and photosynthetic parameters. The k used in the BL approach was simulated using an empirical relationship between k and leaf area index established with the assistance of RT, which showed variation up to 0.2 in k depending on canopy geometry under the same plant density. When a constant k value was used instead, a difference of 0.2 in k resulted in up to 27% loss in accuracy for shoot dry matter. These results suggested that, with the assistance of RT in k estimation, the simple approach BL-HS provided efficient estimation for long-term processes.
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