State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian 361102, China; College of Ocean and Earth Sciences, Xiamen University, Xiamen, Fujian 361102, China.
State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian 361102, China; Department of Marine Sciences, University of Connecticut, Groton, CT, United States of America.
Sci Total Environ. 2022 Aug 1;832:155094. doi: 10.1016/j.scitotenv.2022.155094. Epub 2022 Apr 6.
Nutrient conditions influence the physiology and stoichiometry of marine phytoplankton. While extensive studies have documented the effects of abundances and types of nutrients such as nitrogen (N) and phosphorus (P), the effect of phosphonates as a P source is less understood and underexplored. Here, with the cosmopolitan coccolithophorid Emiliania huxleyi as a model phytoplankter, we investigated the effect of the phosphonate type of herbicide glyphosate as the sole P source in comparison with the P-depleted and P-replete (with 36 μM dissolved inorganic phosphate [DIP]) cultures. We measured changes in cellular C (carbon):P and N:P ratios and physiological performance and documented the corresponding transcriptomic and miRNAomic responses in E. huxleyi to glyphosate treatment. We found that glyphosate supported population growth but not to the full scale relative to DIP, and this was under the concerted regulation of DNA replication and cell cycle arrest genes as well as the growth-regulating miRNA. Furthermore, our data suggest that E. huxleyi took up glyphosate directly, bypassing extracellular hydrolysis, and this involved ABC transporters. Meanwhile, glyphosate-grown cultures displayed marked increases in cellular particulate organic C (POC) and PON contents, cell size, and transcription of genes for CO fixation and citrate cycle, nitrate transport, and protein biosynthesis. However, compared to DIP, the maximum absorption rate of glyphosate was only 33%, and glyphosate-grown E. huxleyi cells exhibited a mild P-stress symptom and elevated cellular C:P and N:P ratios. Interestingly, glyphosate-grown cells showed an increased sinking rate, suggesting that glyphosate as the sole P source might enhance the efficiency of C export by E. huxleyi, which would compensate for the expected decline in primary productivity (and hence carbon efflux) in the future more nutrient-depleted ocean. This biogeochemical implication needs to be further studied and verified, however.
营养条件会影响海洋浮游植物的生理学和化学计量学。虽然大量研究已经记录了氮（N）和磷（P）等营养物质丰度和类型的影响，但作为磷源的膦酸盐的影响却知之甚少且探索不足。在这里，以广布性的颗石藻 Emiliania huxleyi 为模式浮游植物，我们研究了作为唯一磷源的除草剂草甘膦的膦酸盐类型与磷贫化和磷充足（含 36 μM 溶解无机磷 [DIP]）培养物相比的影响。我们测量了细胞 C（碳）：P 和 N：P 比值的变化以及生理性能，并记录了 E. huxleyi 对草甘膦处理的相应转录组和 miRNA 组的响应。我们发现草甘膦支持种群生长，但相对于 DIP 而言，生长规模不足，这是通过 DNA 复制和细胞周期停滞基因以及生长调节 miRNA 的协同调控实现的。此外，我们的数据表明，E. huxleyi 直接摄取草甘膦，绕过细胞外水解，这涉及 ABC 转运体。同时，草甘膦培养物显示出细胞颗粒有机碳（POC）和 PON 含量、细胞大小以及 CO 固定和柠檬酸循环、硝酸盐运输和蛋白质生物合成基因的转录显著增加。然而，与 DIP 相比，草甘膦的最大吸收率仅为 33%，并且草甘膦培养的 E. huxleyi 细胞表现出轻微的磷胁迫症状和升高的细胞 C：P 和 N：P 比值。有趣的是，草甘膦培养的细胞表现出增加的下沉率，这表明草甘膦作为唯一的磷源可能会提高 E. huxleyi 碳输出的效率，这将补偿未来更贫营养的海洋中预计会出现的初级生产力（因此碳外溢）下降。然而，这种生物地球化学意义需要进一步研究和验证。
