A study of ryegrass architecture as a self-regulated system, using functional-structural plant modelling

The canopy structure of grasslands is a major determinant of their use-value, as it affects the quantity and quality of the forage removed when mowed or grazed. The structure of this canopy is determined by individual plant architecture, which is highly sensitive to both environmental variations and management practices such as cutting regimes. In the case of perennial ryegrass (Lolium perenne L.), this architectural plasticity may partially be mediated by a self-regulation process, i.e. the actual state of the architecture (e. g. length of the pseudostem) may indirectly control some morphogenetic processes. To test the robustness of this hypothesis, we designed an exploratory model of ryegrass morphogenesis exhibiting this cybernetic behaviour. This functional-structural model is based on the L-system formalism. It was able to capture satisfactorily the major quantitative architectural traits of ryegrass under non-limiting growing conditions and under a cutting constraint. From these simulation results it appears that (i) self-regulation rules could be of practical use to ryegrass modelling, and (ii) when activated in an integrated model, they are not markedly incompatible with observations.