Determining the functional relationship between co-limiting light and nutrient conditions on phytoplankton growth, 2022

Marine phytoplankton growth has long been found to be biochemically co-limited by light and nutrients including iron, nitrogen, and phosphorus. However, despite agreement that nutrient and light co-limitation exists in many places globally, no laboratory study has generated the data required to explicitly quantify how simultaneous light and nutrient limitation interact to control phytoplankton growth. Influential ecosystem models have largely assumed that growth is limited by either the minimum of two limiting factors or a multiplicative relationship between the two, but these functional relationships can produce vastly different predictions of phytoplankton bloom magnitude, influencing the results of ecosystem models. Here, we present a laboratory experiment that aims to determine the functional relationship between light, nutrients, and phytoplankton growth rate. Unfortunately, due to challenges related to quantifying the nitrate concentration and in achieving a low nitrate limitation term, we were unable to meaningfully distinguish between these two functional relationships.