作者：Lei, P., Zhang, J., Yu, R. et al.

Elevated atmospheric carbon dioxide (CO₂) level reshapes microbial communities in nature, yet its consequences for neurotoxic methylmercury (MeHg) production in waters remain unclear. Here, we show that elevated CO₂ levels (650 and 1000 ppm) consistently reduced net MeHg production across 45 freshwater lakes spanning 1200 longitudinal kilometers, particularly in eutrophic conditions (54-96%). Elevated CO₂-driven shifts in carbon substrates favored hydrogenotrophic methanogens (e.g., Methanobacterium) lacking the hgcA methylation gene over hgcA-harboring acetoclastic strains (e.g., Methanosarcina), decreasing methanogen abundance (18-98% in hgcA copies) and activity (13-53% in net CH4 production) and suppressing Hg methylation. Model simulations predict a 33%-74% global decline in lake MeHg production under future CO₂ scenarios, partially counteract MeHg increases associated with intensified algal blooms under warming. This overlooked pathway highlights the need to integrate interacting climate drivers to improve predictions of MeHg risks in a climate-changing future.

大气二氧化碳（CO₂）浓度升高会改变自然环境中的微生物群落结构，但该变化对水体中神经毒性甲基汞（MeHg）生成过程的影响尚不明确。本研究证实，在横跨1200个经度千米的 45处淡水湖泊中，升高的二氧化碳浓度（650 ppm、1000 ppm）可持续降低甲基汞净生成量，富营养化水体中的降幅尤为显著（54%~96%）。二氧化碳浓度升高改变了碳底物组成，促使产氢型产甲烷菌（如甲烷杆菌属)（不含甲基化基因hgcA）相较于携带hgcA基因的乙酸营养型菌株（如甲烷八叠球菌属）占据竞争优势；该变化造成产甲烷菌丰度（hgcA基因拷贝数下降18%~98%）与活性（甲烷净产出降低 13%~53%）下降，进而抑制汞的甲基化反应。模型模拟结果显示，在未来二氧化碳排放情景下，全球湖泊甲基汞生成量或将下降33%~74%，能够在一定程度上抵消气候变暖引发蓝藻水华加剧所带来的甲基汞增量。此前被忽视的这一作用路径表明，在气候变化背景下，需综合多类耦合气候驱动因子，完善水体甲基汞污染风险的预判工作。

（来源：Nature Communications 2026 Issue 1  DOI: 10.1038/s41467-025-67788-0）