Understanding stoichiometric adjustments in a freshwater plant: Responses to sediment and water nutrient dynamics across lake trophic gradients

Despite ongoing efforts to reduce nutrient inputs, eutrophication continues to disrupt biogeochemical cycles and destabilize freshwater food webs. In this study, we examine the stoichiometric responses of the freshwater plant Myriophyllum spicatum under varied environmental conditions across lakes of differing trophic status. Specimens were collected from lakes with a wide natural range of macro- (C, N, P) and micronutrient (Fe, Cu, Zn) concentration in both water and sediments. We applied the ecological stoichiometry framework and analyzed the relationship between nutrient availability (water and sediments) and the elemental composition of M. spicatum's organs (leaves, stems, and roots). The C : N : P ratios in organs were not affected by eutrophication. Instead, all macro- and micronutrient concentrations differed between plant organs. N concentration was highest in leaves and roots, indicating uptake from both sources. Furthermore, sediments significantly influenced the plant organs' C, P, and Zn concentration, while nutrients in the water column showed no correlation. Leaves demonstrated flexibility in C and Zn concentrations, negatively correlating with sediment levels of these elements. The concentration of micronutrients was highest in the roots. Our results indicate distinct nutrient allocation strategies for different plant organs: leaves are rich in N to support photosynthesis, stems store C and P, aiding growth and reproduction, and roots accumulate micronutrients Fe, Zn, and Cu. It highlights sediments as a critical nutrient source for M. spicatum, shaping its elemental composition. The relationship between organisms' biochemistry, trophic interactions, and their transformation into dead organic matter is crucial for understanding environmental stress impacts on aquatic ecosystems.