State Key Laboratory of Marine Environmental Science & College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China.
State Key Laboratory of Marine Environmental Science & College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China.
Sci Total Environ. 2022 Sep 20;840:156591. doi: 10.1016/j.scitotenv.2022.156591. Epub 2022 Jun 7.
Marine heatwaves (MHWs) are affecting the survival of macroalgae. However, little is known regarding how the impacts of MHWs are regulated by nitrogen availability. In this study, we investigated the physiological and genetic responses of a green-tide macroalga Ulva intestinalis Linnaeus and a commercially cultivated macroalga Gracilariopsis lemaneiformis (Bory) E.Y. Dawson, Acleto & Foldvik under different nitrate conditions to simulated MHWs. Under nitrogen limited conditions (LN), heatwaves did not significantly affect biomass or Fv/Fm of U. intestinalis although it led to an earlier biomass decline due to more reproduction events, and meanwhile an upregulation in genes related to TCA cycle and oxidative phosphorylation was detected, supporting sporulation. Under nitrogen replete conditions (HN), heatwaves did not change biomass, Fv/Fm or photosynthetic pigments but reduced reproduction rate along with insignificant change of oxidative phosphorylation and TCA cycle related genes. Meanwhile, genes related to photosynthesis and glutathione metabolism were upregulated. Regarding G. lemaneiformis, heatwaves reduced its Fv/Fm and photosynthetic pigments content, leading to bleaching and death, and photosynthesis-related genes were also downregulated at LN. Fv/Fm was improved and photosynthesis-related genes were up-regulated by the combination of nitrogen enrichment and heatwaves, whereas G. lemaneiformis remained bleached and died by day 12. Therefore, U. intestinalis could survive heatwaves through shifting to micropropagules at LN and protecting its photosynthesis at HN. In contrast, G. lemaneiformis died of bleaching when suffering heatwaves regardless of nitrogen availability. These findings suggest that in future oceans with eutrophication and MHWs, the harmful alga U. intestinalis may have more advantages over the economic alga G. lemaneiformis.
海洋热浪（MHWs）正在影响宏观藻类的生存。然而，人们对于 MHWs 的影响是如何受到氮素可用性调节的知之甚少。在这项研究中，我们研究了绿潮宏观藻类肠浒苔和一种商业养殖的大型藻类条斑紫菜在不同硝酸盐条件下对模拟 MHWs 的生理和遗传反应。在氮限制条件下（LN），热浪对肠浒苔的生物量或 Fv/Fm 没有显著影响，尽管由于更多的繁殖事件导致生物量更早下降，同时检测到与三羧酸循环和氧化磷酸化相关的基因上调，支持孢子形成。在氮充足条件下（HN），热浪不会改变生物量、Fv/Fm 或光合色素，但会降低繁殖率，同时氧化磷酸化和三羧酸循环相关基因没有明显变化。同时，与光合作用和谷胱甘肽代谢相关的基因上调。对于条斑紫菜，热浪降低了其 Fv/Fm 和光合色素含量，导致白化和死亡，同时 LN 下光合作用相关基因也下调。氮富集和热浪的组合改善了 Fv/Fm 并上调了光合作用相关基因，而条斑紫菜在第 12 天仍处于白化和死亡状态。因此，肠浒苔可以通过在 LN 下转向微繁殖体并在 HN 下保护其光合作用来在热浪中存活。相比之下，条斑紫菜在遭受热浪时无论氮素供应情况如何都会因白化而死亡。这些发现表明，在未来富营养化和 MHWs 的海洋中，有害藻类肠浒苔可能比经济藻类条斑紫菜具有更多优势。
