Positional variation rather than salt stress dominates changes in three-dimensional leaf shape patterns in cucumber canopies

Leaf shape plays a key role in the interaction of a plant with its environment, best-known in the plant’s light harvest. Effects of the environment on the interplay of canopy architecture and physiological functioning can be estimated using functional-structural plant models (FSPMs). In order to reduce the complexity of canopy simulations, leaf shape models used in FSPMs are often simple prototypes scaled to match current leaf area. L-Cucumber is such an FSPM, whose leaf prototype mimics average real leaf shape of unstressed cucumber plants well. However, adaptation processes or stress responses may lead to non-proportional changes in leaf geometries, which, for example, could affect length to width ratios or curvatures. The current leaf shape model in L-Cucumber is static and hence does not incorporate changes in leaf shape within or between plants. Thus, the aim of this study was to estimate leaf shape variation and exemplarily study its effects on FSPM simulations. Three-dimensional leaf coordinate data from a salt stress study were analysed with a robust Bayesian mixed-effects model for estimating leaf shape depending on rank, size and salinity. Results showed that positional and size variation rather than salinity levels dominated 3D leaf shape patterns of cucumber. Considering variable leaf shapes in relation to this main sources of variation in L-Cucumber simulations, only minor effects compared to a realistic, yet static average shape were found. However, with similar computational demands variation in shapes other studies highly sensitive to shape dynamics, for example, pesticide spraying might be affected more strongly.