Xu Xiaoqing, Shao Zhihao, Johnson Matthew D, Zhang Lu, Yang Zhou
Jiangsu Province Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China.
Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA..
Sci Total Environ. 2024 Dec 20;957:177803. doi: 10.1016/j.scitotenv.2024.177803. Epub 2024 Nov 30.
Increasing nitrogen level is one of the most serious environmental problems in global natural waters, disturbing the stability of function and structure of aquatic ecosystem. As important functional group, mixotrophs with plastic metabolism modes perform high adaptations under changing environments, potentially with positive biogeochemical consequences. Here we focus on the trophic plasticity of a model eukaryotic microorganism, mixotrophic Ochromonas under increasing nitrogen and tested the role of osmo-mixotrophy (= mixotrophy) on the physiology of Ochromonas. Results showed that nitrogen eutrophication significantly reduced the proportion of open PSII reaction centers of mixotrophic Ochromonas, and osmo-mixotrophic Ochromonas enhanced the relative contribution of organic carbon uptake with increasing nitrogen. Furthermore, genes involved in photosynthetic electron transfer and photosynthetic carbon fixation were down-regulated, and genes involved in energy metabolism were upregulated. These findings suggested that increasing nitrogen caused mixotrophic organisms to become more heterotrophic, which may bring unexpected impacts to the balance of photosynthesis and respiration within aquatic ecosystem.
氮水平上升是全球天然水体中最严重的环境问题之一，扰乱了水生生态系统功能和结构的稳定性。作为重要的功能类群，具有多种代谢模式的混合营养生物在不断变化的环境中具有高度适应性，可能会产生积极的生物地球化学后果。在此，我们聚焦于一种典型真核微生物——混合营养型赭球藻在氮增加情况下的营养可塑性，并测试渗透混合营养（即混合营养）对赭球藻生理的作用。结果表明，氮富营养化显著降低了混合营养型赭球藻开放PSII反应中心的比例，且渗透混合营养型赭球藻随着氮增加增强了有机碳吸收的相对贡献。此外，参与光合电子传递和光合碳固定的基因被下调，而参与能量代谢的基因被上调。这些发现表明，氮增加导致混合营养生物变得更加异养，这可能给水生生态系统内光合作用和呼吸作用的平衡带来意想不到的影响。
