The Role of Functional Traits and Trade-offs in Seasonal Succession of Phytoplankton Community Structuring : A numerical investigation of resource acquisition traits of Lake Constance

Abstract: Long-term ecological research in deep lakes offers valuable insights into understanding changes in trophic states and organization of phytoplankton assemblages. Utilizing five decades of phytoplankton taxonomic trait data from pre-alpine Lake Constance, a confirmed negative relationship was found between phosphate and light affinity at the annual community trait level. Drawing inspiration from the stronger community-level tradeoff observed between the affinity for phosphate and light among phytoplankton species in Lake Constance, I hypothesized that resource acquisition traits, characterized by the half-saturation constants for nutrient-limited growth (Mi) and light-limited growth (Hi), should exhibit a negative trade-off mechanism at the community mean trait level, derived from the traits of the species in Lake Constance. The developed model was parametrized using empirical data from the lake. Intra- and inter-annual variation in environmental conditions were incorporated in the model by considering seasonal changes in temperature, light intensity, temperature-influenced exchange rates of the vertical water column, and decadal changes in nutrients in Lake Constance. Simulations reflected observed seasonal dominance patterns of phytoplankton species and predicted differences in relative abundance under varying nutrient supplies, aligning with resource limitation trends. Consistent with empirical observations, a negative relationship between light and phosphorous affinity is observed in the 60-year simulation of Lake Constance. The elucidation of such a trade-off mechanism is expected to facilitate the understanding of the coexistence of phytoplankton species in Lake Constance amidst the decadal changes in phosphorus loading by selecting for higher light affinity during eutrophic phases and higher phosphorus affinity during oligotrophic phases.