title: Mixotrophic organisms become more heterotrophic with rising temperature.
abstract: The metabolic theory of ecology predicts that temperature affects heterotrophic processes more strongly than autotrophic processes. We hypothesized that this differential temperature response may shift mixotrophic organisms towards more heterotrophic nutrition with rising temperature. The hypothesis was tested in experiments with the mixotrophic chrysophyte Ochromonas sp., grown under autotrophic, mixotrophic and heterotrophic conditions. Our results show that (1) grazing rates on bacterial prey increased more strongly with temperature than photosynthetic electron transport rates, (2) heterotrophic growth rates increased exponentially with temperature over the entire range from 13 to 33 °C, while autotrophic growth rates reached a maximum at intermediate temperatures and (3) chlorophyll contents during mixotrophic growth decreased at high temperature. Hence, the contribution of photosynthesis to mixotrophic growth strongly decreased with temperature. These findings support the hypothesis that mixotrophs become more heterotrophic with rising temperature, which alters their functional role in food webs and the carbon cycle.
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands. s.wilken@nioo.knaw.nl
authors.forename: Susanne
authors.initials: S
authors.lastname: Wilken
authors.forename: Jef
authors.initials: J
authors.lastname: Huisman
authors.forename: Suzanne
authors.initials: S
authors.lastname: Naus-Wiezer
authors.forename: Ellen
authors.initials: E
authors.lastname: Van Donk
mesh_terms: D052818:Autotrophic Processes / Q000502:physiology*; D052836:Heterotrophic Processes / Q000502:physiology*; D044663:Ochromonas / Q000254:growth & development / Q000502:physiology*; D010788:Photosynthesis; D011157:Population Dynamics; D013696:Temperature