Trophic change has induced substantial changes in biomass and
composition of aquatic communities. Based on phytoplankton data from
Lake Constance we demonstrate that community function is closely
connected to community composition and responds strongly to trophic
change. Community mean traits phosphate affinity and light affinity are
tightly linked to trophic state during eutrophication and
re-oligotrophication, suggesting reversibility of community function.
Phosphate and light affinity are anti-correlated. This anti-correlation
is weak in the species pool distinguished in the dataset, but strong
when weighting the traits by the species biovolumes or when comparing
community mean traits from different trophic states. The emergence of
this tradeoff between phosphate and light affinity indicates competitive
advantage of species with traits near the tradeoff line. The correlation
between community mean maximum growth rate and trophic state turned out
to be spurious and resulted from the development of Dinophyceae spp.
which have an alternative mode of nutrition.