Predicting phytoplankton biomass and estimating critical N:P ratios with piecewise models that conform to Liebig's law of the minimum

Abstract

Summary The influence of nitrogen and phosphorus on the development of phytoplankton biomass is typically such that when one nutrient is limiting, variation in the availability of the other has little effect; this is known as Liebig's law of the minimum. However, statistical models used to quantify the dependence of phytoplankton biomass on both nitrogen and phosphorus availability have typically assumed multiplicative effects of the two nutrients. Here, we demonstrate that a new statistical model, which conforms to this law of the minimum, better describes the response of biomass to nitrogen and phosphorus and in addition provides an estimate of the ratio at which lake phytoplankton communities typically transition between nitrogen and phosphorus limitation. This improvement holds for three large independent sets of lakes, and we conclude that the previous mismatch between the nature of resource limitation and the models used to investigate it may have contributed to an underestimation of the influence of nitrogen on freshwater phytoplankton biomass.