Warming impairs trophic transfer efficiency in a long-term field experiment

In natural ecosystems, the efficiency of energy transfer from resources to consumers determines the biomass structure of food webs. As a general rule, about 10% of the energy produced in one trophic level makes it up to the next^1–3. Recent theory suggests this energy transfer could be further constrained if rising temperatures increase metabolic growth costs⁴, although experimental confirmation in whole ecosystems is lacking. We quantified nitrogen transfer efficiency (a proxy for overall energy transfer) in freshwater plankton in artificial ponds exposed to 7 years of experimental warming. We provide the first direct experimental evidence that, relative to ambient conditions, 4 °C of warming can decrease trophic transfer efficiency by up to 56%. In addition, both phytoplankton and zooplankton biomass were lower in the warmed ponds, indicating major shifts in energy uptake, transformation and transfer^5,6. These new findings reconcile observed warming-driven changes in individual-level growth costs and carbon-use efficiency across diverse taxa^4,7–10 with increases in the ratio of total respiration to gross primary production at the ecosystem level^11–13. Our results imply that an increasing proportion of the carbon fixed by photosynthesis will be lost to the atmosphere as the planet warms, impairing energy flux through food chains, with negative implications for larger consumers and the functioning of entire ecosystems.