CANON in D(esign): Composing scales of plant canopies from phytomers to whole-plants using the composite design pattern

Understanding plant development and architecture has been aided by the phytomer concept. The phytomer, usually considered a vegetative unit of a leaf, node, internode, axillary bud, and occasionally nodal roots, has been extended to the inflorescence with units repeated within and among shoots. For many reasons including insufficient knowledge of phytomer dynamics or specific modelling objectives, crop models may not fully incorporate phytomer concepts. For instance, commonly, some phytomers are aggregated into a single component such as an inflorescence component. Continuing development and maturing of object-oriented (OO) design provides opportunities for better representing phytomer concepts in crop models and integrating approaches using varying scales of resolution. Use of the structural Composite Design Pattern (CDP) in an OO plant design facilitates combining scales with a mixture of single and aggregated phytomers for different components. This paper uses winter wheat (Triticum aestivum L.) to (1) illustrate building the entire plant canopy by the appearance, growth, and death of phytomer units, (2) translate this botanical abstraction into an OO design using the CDP, (3) use the CDP to facilitate a mixture of scales, and (4) present results of a proof-of-concept prototype, CANON, named because the interplay of repeating phytomers is analogous to the repeating melodies of a canon musical composition. CANON implements the phytomer concept of an entire canopy (both vegetative and reproductive phytomers) into an OO design using the CDP. This pattern facilitated the combination of simulation scales from individual reproductive phytomers to an aggregated inflorescence. Quantification of phytomer concepts for winter wheat was primarily derived from the SHOOTGRO model, with the addition of a simple aggregated inflorescence sub-model derived from the APSIM model. The CANON prototype was able to simulate the appearance, growth, and senescence of phytomers on individual shoots of the plant comprising the plant canopy. Importantly, CANON was able to incorporate legacy code with a lower scale of resolution than the phytomer. CANON demonstrates an OO design to simulate plant canopy development and growth from the sub-phytomer to whole-plant level, allowing flexibility in meeting different model objectives and available knowledge of processes.