Modelling the clonal growth of the rhizomatous macrophyte Potamogeton perfoliatus

Macrophytes play a crucial role in the functioning of lake ecosystems. Until now most macrophyte models neglected the fact that the majority of macrophyte species expand clonally during the growing season. Inclusion of a detailed description of clonal growth in models can facilitate our understanding of space occupation and patch expansion and predict future macrophyte development. ¿CLOMO¿ is an individual-based model which includes a detailed, spatially explicit description of rhizome formation and clone expansion as well as a realistic description of photosynthesis including light limitation and temperature. The model also accounts for transfers of energy or resources between different parts of the clone (¿clonal integration¿). Although the clonal growth of macrophytes is complex and poorly known, the first model results for the macrophyte species Potamogeton perfoliatus were promising and compared well with the field data. The model can produce growth networks very similar to those found in the field. A Monte Carlo sensitivity analysis showed systematically which parameters have the largest effect on the architecture and expansion of the clones. The application of the model provided new insights into growth dynamics and patch development: (1) the model showed that a lack of branching will lead to the extinction of the clone after a certain number of years. This is due to the fact that the reproductive organs (turions) are formed at the end of a branch and even a small turion mortality will cause a reduction in surviving plant numbers; (2) the growth of rhizome axes relative to those in the previous year determines the patch density and patch expansion rate. Reversing rhizomes lead to compact patch growth whereas continuing rhizomes lead to loose aggregates.