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

Description du projet

L’impact du déséquilibre du rapport de Redfield sur le phytoplancton

Les écosystèmes aquatiques sont essentiels pour le climat mondial, car ils fournissent plusieurs services écosystémiques, tels que le traitement de l’eau, la régulation du climat et la séquestration du carbone. Toutefois, la modification croissante des cycles de l’azote (N) et du phosphore (P) a perturbé le rapport de Redfield (N:P = 16) dans ces écosystèmes, entraînant des changements significatifs qui affectent négativement la photosynthèse, la diversité et la physiologie du phytoplancton. Cela a un impact sur les services des écosystèmes aquatiques. Ces changements sont encore aggravés par les solutions inefficaces actuelles. Soutenu par le programme Actions Marie Skłodowska-Curie, le projet PHYTOLIM vise à améliorer notre compréhension de la déseutrophisation et de ses effets sur l’écophysiologie et la productivité du phytoplancton. En fin de compte, les résultats serviront à identifier de meilleures solutions pour remédier aux déséquilibres entre l’azote et le phosphore.

Objectif

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.