Headwater organisms are most often simultaneously faced with multiple stressors such as low resource quality and pollutants. Higher food quality has been hypothesized to enhance the tolerance of organisms to pollutants, but the interactive effects of food quality and pollutants on species and ecosystems remain poorly studied. To better understand these interactive effects, we experimentally manipulated the phosphorus (P) content of two leaf litters with contrasted carbon quality (alder and maple). During four weeks, individuals of the detritivorous crustacean Gammarus fossarum were exposed to low levels of cadmium ([Cd] = 0, 0.35 or 0.70 μg L⁻¹) while being fed with one of the leaf P treatments. When organisms were not exposed to Cd, their high survival rate was more driven by the carbon quality of the resource (litter species) than by its stoichiometric quality. In contrast, their number of moults and growth rates were primarily increased by the P content of resources. When exposed to Cd, G. fossarum survival rate was reduced, but this effect was largely magnified by a higher P level in resources. Our results showed that despite positive effects of resource stoichiometric quality on organism life history traits (growth, survival), a resource of high stoichiometric quality might be detrimental for organisms exposed to low and environmentally realistic levels of pollutants. Two non-exclusive hypotheses are proposed to explain these results. First, organisms fed on the highest quality resource exhibited the highest moulting frequencies (moults being the most critical life cycle step of arthropods), which could have rendered them more sensitive to pollutants. Secondly, the metabolism of organisms fed on higher quality resources was potentially enhanced, increasing the uptake of dissolved Cd by gammarids. This study suggests that species sensitivity to pollutants might be underestimated in ecosystems facing both nutrient constraint and pollutants.

上游水生生物通常同时面临多种压力，例如资源质量低和污染物。为了提高生物体对污染物的耐受性，人们提出了更高的食品质量，但是对食品质量和污染物对物种和生态系统的相互作用的研究仍然很少。为了更好地理解这些相互作用的影响，我们通过实验对两个凋落物的磷（P）含量进行了对比，碳含量不同（al木和枫木）。在四个星期内，有害的甲壳类Gammarus fossarum个体暴露于低水平的镉（[Cd] = 0、0.35或0.70μgL ^-1），同时接受一种叶片P处理。当有机体未暴露于Cd时，其高存活率更多地受到资源（垃圾种类）碳质量的驱动，而不是化学计量的质量。相反，它们的蜕皮数和增长率主要是由于资源中P含量的增加。当暴露于Cd时，G。骨s生存率降低了，但是资源P值越高，这种影响就越明显。我们的结果表明，尽管化学计量质量的资源对生物的生活史特征（生长，存活）具有积极影响，但化学计量质量高的资源可能对暴露于低和环境现实水平的污染物的生物有害。提出了两个非排他性的假设来解释这些结果。首先，以最高质量的资源为食的生物表现出最高的换羽频率（换羽频率是节肢动物生命周期中最关键的一步），这可能会使它们对污染物更加敏感。其次，以优质资源为食的生物体的代谢可能得到增强，从而增加了γ-γ对溶解的Cd的吸收。这项研究表明，在面临营养限制和污染物的生态系统中，物种对污染物的敏感性可能被低估了。