One of the most important anthropogenic impacts on freshwater aquatic ecosystems close to intensive agriculture areas is the cumulative increase in herbicide concentrations. The threat is especially relevant for phytoplankton organisms because they have the same physiological targets as the plants for which herbicides have been designed. This led us to explore the evolutionary response of three phytoplanktonic species to increasing concentrations of two herbicides and its consequences in terms of growth and photosynthesis performance. Specifically, we used an experimental ratchet protocol to investigate the differential evolution and the limit of resistance of a cyanobacterium (Microcystis aeruginosa) and two chlorophyceans (Chlamydomonas reinhardtii and Dictyosphaerium chlorelloides) to two herbicides in worldwide use: glyphosate and diuron. Initially, the growth rate of M. aeruginosa and D. chlorelloides was completely inhibited when they were exposed to a dose of 0.23 ppm diuron or 40 ppm glyphosate, whereas a higher concentration of both herbicides (0.46 ppm diuron or 90 ppm glyphosate) was necessary to abolish C. reinhardtii growth. However, after running a ratchet protocol, the resistance of the three species to both herbicides increased by an adaptation process. M. aeruginosa and D. chlorelloides were able to grow at 1.84 ppm diuron and 80 ppm glyphosate and C. reinhardtii proliferated at twice these concentrations. Herbicide-resistant strains showed lower growth rates than their wild-type counterparts in the absence of herbicides, as well as changes on morphology and differences on photosynthetic pigment content. Besides, herbicide-resistant cells generally showed a lower photosynthetic performance than wild-type strains in the three species. These results indicate that the introduction of both herbicides in freshwater ecosystems could produce a diminution of primary production due to the selection of herbicide-resistant mutants, that would exhibit lower photosynthetic performance than wild-type populations.

对集约农业区附近的淡水水生生态系统最重要的人为影响之一是除草剂浓度的累积增加。这种威胁与浮游植物尤其相关，因为它们与除草剂所针对的植物具有相同的生理目标。这促使我们探索三种浮游植物物种对两种除草剂浓度增加的进化反应及其对生长和光合作用性能的影响。具体来说，我们使用实验棘轮方案来研究蓝藻（铜绿微囊藻）和两种绿藻类（莱茵衣藻和小球藻）对两种全球使用的除草剂：草甘膦和敌草隆的差异进化和抗性极限。最初，当铜绿微囊藻和小球藻小球藻暴露于 0.23 ppm 敌草隆或 40 ppm 草甘膦剂量时，它们的生长速率被完全抑制，而需要更高浓度的两种除草剂（0.46 ppm 敌草隆或 90 ppm 草甘膦）消除莱茵衣藻的生长。然而，在执行棘轮方案后，这三个物种对两种除草剂的抗性通过适应过程而增加。铜绿微囊藻和小球藻小球藻能够在 1.84 ppm 敌草隆和 80 ppm 草甘膦浓度下生长，莱茵衣藻在两倍浓度下增殖。在没有除草剂的情况下，除草剂抗性菌株表现出比野生型菌株更低的生长速率，以及形态的变化和光合色素含量的差异。 此外，三个物种中抗除草剂细胞的光合性能普遍低于野生型菌株。这些结果表明，在淡水生态系统中引入两种除草剂可能会由于选择抗除草剂突变体而导致初级生产减少，这些突变体会表现出比野生型种群更低的光合性能。