Temperature is known to stimulate metabolism with cascading effects on multiple biological processes. These effects may, however, vary across processes, types of organisms or levels of biological organisation. They can also vary with nutrient availability, with potentially stronger temperature effects when nutrients are not limiting. This context dependence of temperature effects on processes challenges our ability to anticipate their consequences on ecosystems in a changing world. In headwater streams, the decomposition of allochthonous leaf litter, driven by both microbial decomposers and invertebrates, is known to respond to both temperature and nutrient availability. These food webs are highly tractable and a useful model system to investigate the variations of temperature effects on processes across types of organisms (microbes versus invertebrates), resource availability levels (nutrient concentration), and levels of biological organisation (from individual to ecosystem). In a microcosm experiment, we measured the effects of temperature and nitrogen availability (four levels each) on respiration rates of litter-consuming microbes and invertebrates and their decomposition activity in different contexts of food web complexity. The latter included one treatment without invertebrate detritivore (microbial decomposers only), three single invertebrate taxa (Gammarus, Potamophylax, and Sericostoma) treatments, and one mixed invertebrate taxa treatment (three‐species altogether). Microbial processes increased nearly exponentially with temperature (Arrhenius model, activation energy (± 95% confidence interval) = 0.56 ± 0.53 and 1.00 ± 0.23 eV for litter decomposition and respiration), while invertebrate‐driven processes increased (activation energy from 0.47–1.15 eV) up to a maximal value at an intermediate temperature (c. 11–15°C depending on species and process), above which process rates decreased. By contrast, litter consumption in mixed invertebrate species treatments was not significantly influenced by temperature, because of a negative effect of species mixing occurring above 12°C. Nitrogen had a weaker influence, only slightly stimulating litter consumption by mixed‐species invertebrates, which limited the scope for synergies with temperature effects. Our results raise issues about how aquatic litter consumers meet their energy requirements at high temperature and suggest that a general consequence of warming could be loss of carbon through mineralisation in headwater stream food webs. In several aspects, our results deviate from expectations based on universal relationships between temperature and individual metabolism (e.g. metabolic theory of ecology), suggesting that we may need to develop less simplistic assumptions to predict the consequence of warming on ecosystem processes.

中文翻译：

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异养流过程和生物体之间的变温效应

众所周知，温度会刺激新陈代谢，并对多个生物过程产生连锁效应。然而，这些影响可能因过程、生物体类型或生物组织水平而异。它们也可能随着养分的可用性而变化，当养分不受限制时可能会产生更强的温度影响。温度对过程影响的这种背景依赖性挑战了我们在不断变化的世界中预测其对生态系统后果的能力。在源头溪流中，由微生物分解者和无脊椎动物驱动的外来落叶物的分解已知对温度和养分有效性都有反应。这些食物网非常易于处理，是一个有用的模型系统，可用于研究温度对不同类型生物（微生物与无脊椎动物）、资源可用性水平（营养浓度）和生物组织水平（从个体到生态系统）的过程的影响变化。在一个缩影实验中，我们测量了温度和氮可用性（各有四个水平）对消耗垃圾的微生物和无脊椎动物的呼吸速率的影响及其在食物网复杂性的不同背景下的分解活动。后者包括一种不含无脊椎动物碎屑动物（仅微生物分解者）的处理、三种单一的无脊椎动物类群（Gammarus、Potamophylax 和 Sericostoma）处理，以及一种混合无脊椎动物类群的处理（共三个物种）。微生物过程几乎随温度呈指数增加（Arrhenius 模型，活化能（± 95% 置信区间）= 0.56 ± 0.53 和 1.00 ± 0.23 eV 凋落物分解和呼吸），而无脊椎动物驱动的过程增加（活化能从 0.47-1.15 eV ) 在中间温度（c. 11–15°C，取决于物种和过程）下达到最大值，高于此温度，过程速率会降低。相比之下，混合无脊椎动物物种处理的凋落物消耗不受温度的显着影响，因为物种混合发生在 12°C 以上的负面影响。氮的影响较弱，仅略微刺激混种无脊椎动物的凋落物消耗，这限制了与温度效应的协同作用范围。我们的结果提出了关于水生垃圾消费者如何在高温下满足他们的能量需求的问题，并表明变暖的一般后果可能是通过源头流食物网中的矿化而损失碳。在几个方面，我们的结果偏离了基于温度和个体代谢之间普遍关系的预期（例如生态学的代谢理论），这表明我们可能需要制定不那么简单的假设来预测变暖对生态系统过程的后果。