Interactive effects of warming and eutrophication on zooplankton could reverse the stoichiometric mismatch with phytoplankton

The core ecosystem functioning (e.g. trophic transfer efficiency) is at risk of being disrupted by the growing mismatch between nutrient content of primary producers and nutrient demand of grazing consumers. Ecological stoichiometry provides a conceptual framework that explains this trophic interaction using C, N and P elemental composition across trophic levels. In light of ongoing climate change and eutrophication, previous studies have raised concerns regarding the growing stoichiometric mismatch between phytoplankton and zooplankton, given the stoichiometric plasticity of phytoplankton. However, there is currently little conclusive evidence on the stoichiometric mismatch from a dual perspective of phytoplankton and zooplankton. To address this, we conducted a mesocosm experiment to investigate the separate and combined effects of climate warming (a constant increase of +3.5 ​°C plus heat waves) and eutrophication (nutrient addition) on stoichiometric mismatch between phytoplankton and zooplankton by examining stoichiometric changes in both communities. We observed a growing trend in stoichiometric mismatches when warming or nutrient addition acted individually, which was mediated by the increase in nutrient demand (N, P elements) of zooplankton growth. However, when these stressors acted jointly, the mismatches were reversed. This could be because climate warming and eutrophication combined would lead to changes in species composition, which accordingly reshaped the stoichiometric composition at the community level. These results illustrate the need of stoichiometric mismatches for understanding the implication of global change on trophic interactions and ecosystem functioning, requiring consideration not only of cross-trophic levels but also of compositional changes within communities.