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The second life of terrestrial and plastic carbon as nutritionally valuable food for aquatic consumers
Summary
Researchers used carbon-13-labeled experiments to trace how terrestrial leaves, lignin, and polystyrene microplastics are processed through a four-level aquatic food web from microbes to fish. While microbes could synthesize amino acids and lipids from plant-derived carbon, they produced far fewer nutritional biomolecules from polystyrene, and the resulting molecules were still incorporated into zooplankton and fish tissues. The study shows that plastic carbon can move through food webs and become part of animal body tissues, though at reduced nutritional value, raising concerns about the long-term health of aquatic ecosystems and the quality of fish consumed by humans.
Primary production is the basis for energy and biomolecule flow in food webs. Nutritional importance of terrestrial and plastic carbon via mixotrophic algae to upper trophic level is poorly studied. We explored this question by analysing the contribution of osmo- and phagomixotrophic species in boreal lakes and used 13 C-labelled materials and compound-specific isotopes to determine biochemical fate of carbon backbone of leaves, lignin-hemicellulose and polystyrene at four-trophic level experiment. Microbes prepared similar amounts of amino acids from leaves and lignin, but four times more membrane lipids from lignin than leaves, and much less from polystyrene. Mixotrophic algae (Cryptomonas sp.) upgraded simple fatty acids to essential omega-3 and omega-6 polyunsaturated fatty acids. Labelled amino and fatty acids became integral parts of cell membranes of zooplankton (Daphnia magna) and fish (Danio rerio). These results show that terrestrial and plastic carbon can provide backbones for essential biomolecules of mixotrophic algae and consumers at higher trophic levels.