Mechanistic modelling of coupled phloem/xylem transport for L-systems: combining analytical and computational methods

Transport of carbohydrates and water are essential aspects of plant function. The aim of this study was to develop and test the methods for mechanistic modelling of quasi-stationary coupled phloem/xylem transport in the context of functional-structural plant modelling.The novelty of this approach is in combining analytical and computational methods. The plant structure is modelled at a metamer level with the internodes represented by conduit elements and the lateral organs represented by sources and sinks. Transport equations are solved analytically for each internode and then the solutions are adjusted and 'sewn' together using an iterative computational procedure taking into account concentration-dependent sinks and sources. The model is implemented in L-studio and uses the aspect-oriented modelling approach for phloem/xylem coupling.To our knowledge, this is the first transport model that provides continuous distributions of the system variables in a complex developing structure. The model takes into account non-linear dependence of phloem resistance and osmotic potential on the local carbohydrate concentration. The model solutions show excellent agreement with the existing results of other analytical and numerical models. These comparisons confirm the validity of the approximations made in the model. Combining analytical and computational methods made it possible to take into account continuous sink/source distribution within internodes without much increase in the complexity of the computational procedure, because the necessary changes in the model were mostly in the analytical part. The results emphasize sensitivity of phloem flux and lateral xylem flux to the presence of distributed sinks and sources along the transport system.The presented approach provides a new insight into mechanistic modelling of phloem/xylem transport in growing plants. It will be useful for both fine-scale modelling of carbohydrate dynamics and for creating simpler models at a growth unit level

After initial invigoration by heading, young pear trees show reduction in axis vigour and increased propensity to flower

Fast establishment of the canopy in young trees, followed by reduced vegetative vigour and precocity are desirable traits in fruit production. Severe heading (cutting back the primary axis of the tree after the first year of growth) to induce branching is a nursery practice to increase early fruit yield. Our aim was to provide a systematic study of the responses of young pear trees to severe heading. We used an experimental system with two scion genotypes and three rootstocks to create trees with contrasting branching habits and vigour. The trees' trunks were headed and a single bud was allowed to outgrow in the following season. Architectural analysis was used to quantify the development of regenerated trees. In the first year after heading, the growth of the primary axes and, depending on the scion genotype, the sylleptic branching of regenerating trees, were invigorated. In the second year, the percentage of budbreak was also increased, but the shoot growth was greatly reduced. Axis propensity to flower in spring of the third year of growth was increased. The new insights into the effects of heading on tree aging and flowering will be used for guiding the best approaches to managing young pear trees

A functional–structural kiwifruit vine model integrating architecture, carbon dynamics and effects of the environment

Background and Aims Functional-structural modelling can be used to increase our understanding of how different aspects of plant structure and function interact, identify knowledge gaps and guide priorities for future experimentation. By integrating existing knowledge of the different aspects of the kiwifruit (Actinidia deliciosa) vine's architecture and physiology, our aim is to develop conceptual and mathematical hypotheses on several of the vine's features: (a) plasticity of the vine's architecture; (b) effects of organ position within the canopy on its size; (c) effects of environment and horticultural management on shoot growth, light distribution and organ size; and (d) role of carbon reserves in early shoot growth

Towards aspect-oriented functional-structural plant modelling

Background and Aims Functional-structural plant models (FSPMs) are used to integrate knowledge and test hypotheses of plant behaviour, and to aid in the development of decision support systems. A significant amount of effort is being put into providing a sound methodology for building them. Standard techniques, such as procedural or object-oriented programming, are not suited for clearly separating aspects of plant function that criss-cross between different components of plant structure, which makes it difficult to reuse and share their implementations. The aim of this paper is to present an aspect-oriented programming approach that helps to overcome this difficulty