Mercury(Hg) is a potent neurotoxin, and as a persistent global pollutant, it poses a serious threat to ecosystems and human health. The absorption of gaseous elemental mercury [Hg(0)] by terrestrial vegetation is a major mechanism for the removal of atmospheric mercury. Currently, climate change is profoundly affecting the growth and physiological processes of global terrestrial vegetation, but its impact on mercury absorption remains unclear.
To investigate this scientific issue, the atmospheric science team led by Professor Zhang Yanxu utilized the newly developed global terrestrial Hg model and field data from global change control experiments. By integrating models and meta-analysis methods across interdisciplinary fields such as atmospheric science, ecology, environmental science, and plant physiology, they quantitatively assessed the impact of various global change factors on the Hg absorption of terrestrial vegetation under different emission scenarios. The study shows that the future increase in atmospheric CO2 concentration severely inhibits the flux of atmospheric Hg absorbed by global vegetation. This is because under the strong fertilization effect, plant leaves close their stomata to reduce transpiration, leading to a weakened capacity for vegetation to absorb Hg. This potential carbon-Hg decoupling phenomenon challenges the traditional theories of carbon-Hg coupling in terrestrial ecosystems over the past few decades.
Figure 1 Schematic diagram
The research found that compared to other climate change factors, the biogeochemical effects of CO2 are the dominant factor regulating the future global vegetation's absorption of atmospheric Hg. For every 100 ppm increase in atmospheric CO2 concentration, the Hg concentration inside plant leaves decreases by approximately 5.87%, and different vegetation functional types exhibit varying sensitivities to this response, with crop types being the most sensitive. The underlying phenomenon is the complex interaction mechanisms between Hg, carbon, and water within terrestrial ecosystems. The biogeochemical effects of increased CO2 concentration enhance plant photosynthesis while also resulting in water loss. In response, plants reduce their stomatal conductance to decrease transpiration, leading to a decrease in stomatal conductance and subsequently altering the rate of Hg absorption by plant leaves.
Figure 2 The impact of increased CO2 concentrations on the absorption of Hg(0) by different vegetation functional types globally.
Model predictions under the high emission scenario (SSP5-8.5) indicate that, by the end of this century, the amount of atmospheric elemental Hg absorbed by vegetation will decrease by nearly 60% compared to the present day. This means that a large amount of Hg will bypass the sequestration by plants and soil, flowing into rivers and oceans, where it forms methylmercury that accumulates in aquatic food chains, posing a significant threat to human health. Therefore, this study suggests that this climate-related Hg health risk should be considered when assessing the effectiveness of the Minamata Convention, and it also emphasizes that measures to reduce human carbon emissions are still urgently needed.
Figure 3 The biogeochemical effects of increased CO2 concentrations on the absorption of Hg(0) by global vegetation.
The findings were published online on May 27, 2024, in the journal Nature Communications under the title Potential decoupling of CO2 and Hg uptake process by global vegetation in the 21st century. Professor Zhang Yanxu from the School of Atmospheric Sciences at Nanjing University is the corresponding author of the paper, and Tengfei Yuan, a Ph.D. student from the class of 2021, is the first author. The co-authors of the paper include Professor Guo Weidong, Assistant Professor Ge Jun, Dr. Song Zhengcheng, Dr. Miao Xin, Ph.D. candidates Huang Shaojian, Zhang Peng, Wang Yujuan, Pang Qiaotong, Peng Dong, Wu Peipei from our school, Professor Guo Hongyan from the School of Environmental Science, Professor Shao Junjiong from Zhejiang A&F University, Dr. Zhang Peipei from the Chengdu Institute of Biology, Chinese Academy of Sciences, and Dr. Wang Yabo from Yangzhou University. This work was supported by the the National Natural Science Foundation of China (NSFC) 42394094, the “GeoX” Interdisciplinary Research Funds for the Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, the Fundamental Research Funds for the Central Universities (grant no. 14380188, 14380168), the Frontiers Science Center for Critical Earth Material Cycling, and the Collaborative Innovation Center of Climate Change, Jiangsu Province.
Article link: Yuan, T., Huang, S., Zhang, P. et al. Potential decoupling of CO2 and Hg uptake process by global vegetation in the 21st century. Nat Commun 15, 4490 (2024). https://doi.org/10.1038/s41467-024-48849-2