Stoichiometric flexibility in response to fertilization along gradients of environmental and organismal nutrient richness

Ecosystems globally are undergoing rapid changes in elemental inputs. Because nutrient inputs differently impact high- and low-fertility systems, building a predictive framework for the impacts of anthropogenic and natural changes on ecological stoichiometry requires examining the flexibility in stoichiometric responses across a range of basal nutrient richness. Whether organisms or communities respond to changing conditions with stoichiometric homeostasis or flexibility is strongly regulated by their species-specific capacity for nutrient storage, relative growth rate, physiological plasticity, and the degree of environmental resource availability relative to organismal demand. Using a meta-analysis approach, we tested whether stoichiometric flexibility following nutrient enrichment correlates with the relative fertility of terrestrial and aquatic systems or with the initial stoichiometries of the organism or community. We found that regardless of limitation status, N-fertilization tended to significantly reduce biota C:N and increase N:P, and P fertilization reduced C:P and N:P in both terrestrial and aquatic systems. Further, stoichiometric flexibility in response to fertilization tended to decrease as environmental nutrient richness increased in both terrestrial and aquatic systems. Positive correlations were also detected between the initial biota C:nutrient ratio and stoichiometric flexibility in response to fertilization. Elucidating these relationships between stoichiometric flexibility, basal environmental and biota fertility, and fertilization will increase our understanding of the ecological consequences of ongoing nutrient enrichment across the world.