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^1,2,3. 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 transfer^5,6. These findings reconcile observed warming-driven changes in individual-level growth costs and in carbon-use efficiency across diverse taxa^4,7,8,9,10 with increases in the ratio of total respiration to gross primary production at the ecosystem level^11,12,13. 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.

在生态系统中，从资源到消费者的能量转移效率决定了食物网的生物量结构。作为一般规则，大约 10% 的能量在一个营养级产生，使其达到下一个^1,2,3。最近的理论表明，如果温度升高会增加新陈代谢的生长成本，这种能量转移可能会受到进一步限制⁴，尽管缺乏对整个生态系统的实验确认。在这里，我们量化了人工池塘中淡水浮游生物的氮转移效率（整体能量转移的代表），这些浮游生物已经暴露于七年的实验性变暖。我们提供直接的实验证据表明，相对于环境条件，升温 4 °C 可使营养转移效率降低多达 56%。此外，在变暖的池塘中，浮游植物和浮游动物的生物量都较低，这表明能量吸收、转化和转移发生了重大变化^5,6。这些发现调和了观察到的变暖驱动的个体水平增长成本和不同分类群的碳利用效率的变化^4,7,8,9,10随着生态系统一级总呼吸与初级生产总值之比的增加^11,12,13。我们的研究结果表明，随着地球变暖，通过光合作用固定的碳中越来越多的碳将流失到大气中，从而削弱通过食物链的能量通量，这将对更大的消费者和整个生态系统的运作产生负面影响。