A critical assessment of the stoichiometric knife-edge: no evidence for artifacts caused by the experimental P-supplementation of algae

Abstract The stoichiometric knife-edge refers to the reduced performance of consumers encountering food with excess phosphorus (P) relative carbon (C) or nitrogen (N). Studies that provide evidence for such in aquatic systems often apply phosphate supplementation create P-rich treatments. However, this method may suffer from artifacts, because after uptake algae store P a form different biomolecules typically consumed by zooplankton. Our aim was test if results potential biases. We experimentally exposed populations herbivore rotifer species, Brachionus calyciflorus (Pallas), four quality treatments: grown under P-saturating (HP chem , molar C:P ratio = 59.7 ± 2.7) and P-sufficient (MP 116.3 5.2) conditions chemostats, P-limiting conditions, but ratios equal HP MP treatments, respectively LP+P 59.8 0.14; 121.0 4.3). latter two treatments were achieved through P-supplementation P-limited algae. Results show rotifers fed either intermediate content, population growth rates consistently higher on chemostats than treated method. Importantly, also lower magnitude negative impact independent algal history. result confirms existence indicates is reliable study effect zooplankton standardized way.