Heterotrophic microbes upgrade food value of a terrestrial carbon resource for Daphnia magna.

Terrestrial carbon resources are generally regarded as inferior‐quality food for zooplankton due to a lack of essential biomolecules (e.g., polyunsaturated fatty acids). However, recent stable isotopic studies have suggested terrestrial carbon to be substantial resource for zooplankton, though the mechanisms of assimilation are not well understood. Here, we consider the possibility that heterotrophic microbes can upgrade the nutritional value of terrestrial carbon and thereby support the somatic growth and reproduction of zooplankton. To test this hypothesis, a simplified experimental food chain was established. Aquatic microbes were raised under dark laboratory conditions on a terrestrial carbon source, decaying corn straw (Zea mays L.), and the resulting degradation products were supplied as food to Daphnia magna. Significant increases in microbial abundance and concomitant increases in polyunsaturated fatty acid were observed during the degradation of corn straw. Furthermore, experiments indicated that the somatic growth and reproduction of D. magna was supported exclusively by the products of corn straw decay. Our results indicate a pathway for the assimilation of terrestrial carbon by zooplankton, in which heterotrophic microbes serve as trophic links. [ABSTRACT FROM AUTHOR]