Phytoplankton photosynthesis and physiology under P limitation within a context of diversity

Aquatic ecosystems offer a wide range of ecosystem services (e.g., climate regulation, carbon sequestration, water treatment, and fisheries).

In these ecosystems, Nitrogen (N) and Phosphorus (P) cycles have been modified, leading to an increase in nutrient concentration and changes in the stoichiometry of the element.

In marine systems, dissolved N and P are, on average, present in an overall stoichiometry balance called the Redfield ratio (N:P=16).

The skewness of stoichiometry is exacerbated by a general effort of countries to reverse eutrophication by reducing only P using water treatment plants.

This management solution is leading to a global increase of the N:P in the freshwater and coastal marine systems, amplifying the likelihood of P limitation. Phytoplankton that supports the entire trophic web follows the Redfield ratio and is affected by this unbalanced ratio.

Photosynthesis, diversity and physiology of the phytoplankton communities are deeply impacted by these changes, thus stressing the need for understanding this arising issue.

This project aims to evaluate how reverse eutrophication (causing high N:P) affects the ecophysiology and productivity of phytoplankton.

To explore this issue, nutrient experiments at an unbalanced nutrient ratio (N:P = 90) will be performed with a selection of freshwater and marine species to investigate species on the whole water continuum.

An increasing diversity (single species; co-cultures; natural communities for freshwater only) gradient will be used while chemical, physiological, photosynthetic and diversity parameters will be measured.

This also includes a temperature variation experiment to study the combined issue of climate change reverse and eutrophication.

The information delivered by this project will be critical both for the understanding of the response of phytoplankton communities under unbalanced input and for the problem of reverse eutrophication and climate change to improve water management.