Nitrogen fixation may not alleviate stoichiometric imbalances that limit primary production in eutrophic lake ecosystems.

Ecosystem-scale primary production may be proximately limited by nitrogen (N) but ultimately limited by phosphorus (P) because N fixation contributes new N that accumulates relative to P at ecosystem scales. However, the duration needed to transition between proximate N limitation and ultimate P limitation remains unknown for most ecosystems, including lakes. Here we present the results of a fully replicated, multi-annual lake mesocosm experiment that permitted full air-water-sediment interactions that mimicked lake ecosystem ecology.