Freshwater mesocosm experiment 2012 in Vancouver, Canada on effects of increased temperature and food chain length on oxygen fluxes and plankton community structure

Over broad thermal gradients, the effect of temperature on aerobic respiration and photosynthesis rates explains variation in community structure and function. Yet for local communities, temperature dependent trophic interactions may dominate effects of warming. We tested the hypothesis that food chain length modifies the temperature-dependence of ecosystem fluxes and community structure. In a multi-generation aquatic food web experiment, increasing temperature strengthened a trophic cascade, altering the effect of temperature on estimated mass-corrected ecosystem fluxes. Compared to consumer-free and 3-level food chains, grazer-algae (2-level) food chains responded most strongly to the temperature gradient. Temperature altered community structure, shifting species composition and reducing zooplankton density and body size. Still, food chain length did not alter the temperature dependence of net ecosystem fluxes. We conclude that locally, food chain length interacts with temperature to modify community structure, but only temperature, not food chain length influenced net ecosystem fluxes.

在较宽的温度梯度范围内，温度对有氧呼吸速率（aerobic respiration rate）与光合速率（photosynthesis rate）的作用可解释群落结构与功能的变异。然而针对本地群落，温度依赖型营养相互作用（temperature-dependent trophic interactions）或许会主导增温的影响。本研究检验了如下假说：食物链长度（food chain length）会改变生态系统通量（ecosystem fluxes）与群落结构的温度依赖性。在一项多代次水生食物网（aquatic food web）实验中，温度升高强化了营养级联效应（trophic cascade），进而改变了温度对经估算的生物量校正（mass-corrected）生态系统通量的影响。相较于无消费者（consumer-free）食物链与3级食物链，植食者-藻类（grazer-algae，2级）食物链对温度梯度的响应最为强烈。温度改变了群落结构，使物种组成发生偏移，并降低了浮游动物（zooplankton）的密度与个体体型。尽管如此，食物链长度并未改变净生态系统通量（net ecosystem fluxes）的温度依赖性。本研究得出结论：在本地尺度下，食物链长度与温度相互作用以调控群落结构，但仅温度（而非食物链长度）会对净生态系统通量产生影响。