Massive use of glyphosate-based herbicides in agricultural activities has led to the appearance of this herbicide in freshwater systems, which represents a potential threat to these systems and their communities. These herbicides can affect autotrophic and heterotrophic picoplankton abundance. However, little is known about glyphosate impact on the whole structure of these assemblages. Herein, we used an 8-day long microcosm approach under indoor controlled conditions to analyze changes in the structure of picoplankton exposed to a single pulse of glyphosate. The analyzed picoplankton correspond to two outdoor ponds with contrasting states: "clear" (chlorophyll-a = 3.48 μg L-1± 1.15; nephelometric turbidity, NTU = 1) and "turbid" (chlorophyll-a = 105.96 μg L-1 ± 15.3; NTU = 48). We evaluated herbicide impact on different picoplankton cytometric populations and further explored changes in bacterial dominant operational taxonomic units (OTUs) fingerprinting. We observed that glyphosate induced a drastic decrease in the abundance of phycocyanin-rich picocyanobacteria. Particularly, in the turbid system this effect resulted in an 85 % decrease in the abundance of the whole autotrophic picoplankton. Glyphosate also changed the structure of the heterotrophic fraction by means of changing bacterial dominant OTUs fingerprinting patterns in both systems and by shifting the relative abundances of cytometric groups in the clear scenario. These results demonstrate that upon glyphosate exposure picoplanktonic fractions face not only the already reported changes in abundance, but also alterations in the composition of cytometric groups and of bacterial dominant operational taxonomic units. This research provides suitable and still little explored tools to analyze agrochemical effects on picoplanktonic communities.

中文翻译：

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草甘膦对自养和异养微微浮游生物结构影响的新发现：一个缩影方法。

在农业活动中大量使用草甘膦基除草剂导致该除草剂出现在淡水系统中，这对这些系统及其社区构成了潜在威胁。这些除草剂会影响自养和异养微微浮游生物的丰度。但是，关于草甘膦对这些组合物整体结构的影响知之甚少。在这里，我们在室内受控条件下使用了一个为期8天的缩影方法来分析暴露于单次草甘膦脉冲下的浮游生物结构的变化。所分析的微微浮游生物对应于两个具有相反状态的室外池塘：“透明”（叶绿素a = 3.48μgL-1±1.15；浊度浊度，NTU = 1）和“混浊”（叶绿素a = 105.96μgL-1± 15.3； NTU = 48）。我们评估了除草剂对不同的浮游生物细胞计数种群的影响，并进一步探索了细菌显性操作分类单位（OTU）指纹图谱的变化。我们观察到草甘膦引起富含藻蓝蛋白的微蓝细菌的丰度急剧下降。特别是在浑浊的系统中，这种作用导致整个自养微微浮游生物的丰度降低了85％。草甘膦还通过改变两个系统中细菌占主导地位的OTU指纹图谱以及在清晰的情况下移动细胞计数组的相对丰度来改变异养级分的结构。这些结果表明，在草甘膦暴露后，微浮游生物级分不仅面临已经报道的丰度变化，而且还会改变细胞计数组和细菌主要操作分类单元的组成。这项研究提供了合适的，仍很少探索的工具来分析农用化学物质对微浮游生物群落的影响。