Phosphorus enrichment of stream ecosystems generally increases primary production in the benthos, but the consequences of eutrophication for the nutritional quality of periphyton for grazers are less clear. On short timescales, high phosphorus inputs may lead to reduced C:P ratios and high essential fatty acid contents of periphyton, which are both considered important determinants of food quality for grazers. However, nutrient enrichment may alter the taxonomic composition of periphyton and favor the growth of less palatable algal taxa. In this study, periphyton was grown under a gradient of dissolved phosphorus availability from 5 to 100 µg P · L⁻¹, to investigate eutrophication effects on periphyton taxonomy, C:N:P stoichiometry, and fatty acid composition. After 1 month, periphyton grown under oligotrophic conditions was mainly composed of diatoms (~86%). With increasing phosphorus availability, diatoms were gradually outcompeted by chlorophytes and cyanobacteria, which were the predominant taxon under eutrophic conditions. Unexpectedly, periphyton C:P ratios increased with greater phosphorus supply, from ~280 under oligotrophic conditions up to ~790 at 100 µg · L⁻¹, reflecting a tendency of chlorophytes and cyanobacteria to produce more biomass per unit of assimilated phosphorus compared to diatoms. Periphyton content of essential polyunsaturated fatty acids relative to biomass followed a unimodal relationship with phosphorus availability and peaked at intermediate phosphorus levels, likely as a result of both taxonomic and nutrient effects. Our results demonstrate that phosphorus‐driven eutrophication of freshwater ecosystems may worsen periphyton nutritional quality due to taxonomic sorting, which may further lead to lower growth and reproduction of herbivores.

中文翻译：

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磷梯度上的生物分类变化会影响水系附生植物的化学计量和脂肪酸组成。

溪流生态系统的磷富集通常会增加底栖动物的初级产量，但是富营养化对放牧者周生植物营养质量的影响尚不清楚。在较短的时间范围内，高磷输入量可能导致降低的C：P比值和高植物壁藻的必需脂肪酸含量，这两者均被认为是放牧者食品质量的重要决定因素。但是，营养物的富集可能会改变周生植物的分类学组成，并有利于不太可口的藻类类群的生长。在这项研究中，水生植物在溶解磷可利用量从5到100 µg P·L ^-1的梯度下生长，以研究富营养化对浮游植物分类学，C：N：P化学计量和脂肪酸组成的影响。1个月后，在贫营养条件下生长的附生植物主要由硅藻组成（约86％）。随着磷利用率的提高，硅藻逐渐被富营养条件下的主要分类群-叶绿素和蓝细菌所竞争。出乎意料的是，随着磷供应的增加，浮游植物的C：P比值从富营养条件下的〜280增加到100 µg·L ^-1时的〜790与硅藻相比，反映了绿化植物和蓝细菌倾向于每单位吸收的磷产生更多的生物量。必需多不饱和脂肪酸相对于生物质的附生植物含量与磷的利用率呈单峰关系，并可能在生物磷和营养效应的共同作用下达到中等磷水平。我们的研究结果表明，由于分类学的分类，磷驱动的淡水生态系统富营养化可能会恶化周生植物的营养质量，这可能进一步导致草食动物的生长和繁殖降低。