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In 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 next1–3. Recent theory suggests that this energy transfer could be further constrained if rising temperatures increase metabolic growth costs4, although experimental confirmation in whole ecosystems is lacking. Here we quantify nitrogen transfer efficiency—a proxy for overall energy transfer—in freshwater plankton in artificial ponds that have been exposed to seven years of experimental warming. We provide direct experimental evidence that, relative to ambient conditions, 4 °C of warming can decrease trophic transfer efficiency by up to 56%. In addition, the biomass of both phytoplankton and zooplankton was lower in the warmed ponds, which indicates major shifts in energy uptake, transformation and transfer5,6. These findings reconcile observed warming-driven changes in individual-level growth costs and in carbon-use efficiency across diverse taxa4,7–10 with increases in the ratio of total respiration to gross primary production at the ecosystem level11–13. 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, which will have negative implications for larger consumers and for the functioning of entire ecosystems. In artificial ponds exposed to seven years of experimental warming, energy transfer between two trophic levels of freshwater plankton decreased by 56% and the biomass of both levels was reduced.

In 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

5 pages, 2 figures, 1 table., Ecosystem respiration is the biotic conversion of organic carbon to carbon dioxide by all of the organisms in an ecosystem, including both consumers and primary producers. Respiration exhibits an exponential temperature dependence at the subcellular and individual levels1, but at the ecosystem level respiration can be modified by many variables2, 3, 4 including community abundance and biomass5, which vary substantially among ecosystems6. Despite its importance for predicting the responses of the biosphere to climate change, it is as yet unknown whether the temperature dependence of ecosystem respiration varies systematically between aquatic and terrestrial environments. Here we use the largest database of respiratory measurements yet compiled to show that the sensitivity of ecosystem respiration to seasonal changes in temperature is remarkably similar for diverse environments encompassing lakes, rivers, estuaries, the open ocean and forested and non-forested terrestrial ecosystems, with an average activation energy similar to that of the respiratory complex3 (approximately 0.65 electronvolts (eV)). By contrast, annual ecosystem respiration shows a substantially greater temperature dependence across aquatic (approximately 0.65 eV) versus terrestrial ecosystems (approximately 0.32 eV) that span broad geographic gradients in temperature. Using a model5 derived from metabolic theory7, these findings can be reconciled by similarities in the biochemical kinetics of metabolism at the subcellular level, and fundamental differences in the importance of other variables besides temperature—such as primary productivity and allochthonous carbon inputs—on the structure of aquatic and terrestrial biota at the community level, G.Y.-D., M.T. and G.W. acknowledge the support of the Natural Environment Research Council, UK (grant NE/F004753/1) for financial support. P.A.S. was funded by the Danish Council for Independent Research, Natural Sciences grant 10-085238 and the Danish Centre for LakeRestoration(CLEAR). J.P. acknowledges the Academyof Finland Centre of Excellence program (project number 218094) for funding. J.M.M. was supported by a Ramon y Cajal Fellowship (RYC-892 2008-03664), a Ministry of Economygrant (CGL2010-20091) and Generalitat de Catalunya grant (2009SGR142)