PEI-CHI HOChang, Chun-WeiChun-WeiChangShiah, Fuh-KwoFuh-KwoShiahPEI-LING WANGCHIH-HAO HSIEHAndersen, Ken H.Ken H.Andersen2024-10-252024-10-252020-04-0100030147https://www.scopus.com/record/display.uri?eid=2-s2.0-85081309985&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/722459Trophic strategy determines stoichiometry of plankton. In general, heterotrophic zooplankton have lower and more stable C:N and C:P ratios than photoautotrophic phytoplankton, whereas mixotrophic protists, which consume prey and photosynthesize, have stoichiometry between zooplankton and phytoplankton. As trophic strategies change with cell size, body size may be a key trait influencing eukaryotic plankton stoichiometry. However, the relationship between body size and stoichiometry remains unclear. Here we measured plankton size-fractionated C:N ratios under different intensities of light and nutrient supply in subtropical freshwater and marine systems. We found a unimodal body size–C:N ratio pattern, with a maximum C:N ratio at ~50 mm diameter in marine and freshwater systems. Moreover, the variation in C:N ratios is explained mainly by body size, followed by light intensity and nutrient concentration. To investigate the mechanisms behind this unimodal pattern, we constructed a size-based plankton food web model in which the trophic strategy and C:N ratio are an emerging result. Our model simulations reproduce the unimodal pattern with a C:N ratio of photoautotrophs ≤50 mm increasing with body size due to increase of photosynthetic carbon, whereas C:N ratios of organisms >150 μm decrease with size due to decreasing photoautotrophic but increasing heterotrophic uptake. Based on our field observations and simulation, we extend the classic “light-nutrient” theory that determines plankton C:N ratio to include body size and trophic strategy dependency. We conclude that body size and size-dependent uptake of resources (light, nutrients, and prey) determine plankton stoichiometry at various light and nutrient supplies.falseEcological stoichiometryMixotrophySize-based resource affinityTrophic strategy[SDGs]SDG13[SDGs]SDG14journal article10.1086/7073942-s2.0-85081309985