Effects and mechanisms of warming on the relationship between soil organic matter degradation and methylmercury production in Hg-contaminated soil

• Hg stress does not change GHG production but enhances the Q 10 of SOM degradation. • The Q 10 increase caused by Hg stress is associated with shifts in microbial life strategies. • Warming had minimal impact on MeHg production in contaminated soils. • Hg spike cause a shift from a positive to a negative correlation between GHG and MeHg. The degradation of soil organic matter (SOM) is an essential process that not only drives the production of greenhouse gases (GHGs) but also influences the environmental fate of pollutants, such as mercury (Hg), specifically methylmercury (MeHg) production. However, the relationship between these processes and their response to warming remains unclear. To address this gap, we conducted a 60-day microcosm incubation period using mimic-contaminated soils with varying Hg levels to investigate the effects of warming on SOM degradation and MeHg production. These results indicate that Hg stress does not significantly affect GHG production but increases the temperature sensitivity (Q 10 ) of SOM degradation. This implies that warming increases the feedback of carbon release in contaminated soil, particularly when considering seasonal temperature dynamics or prospective global warming scenarios. Additionally, warming can significantly promote GHG production. However, warming did not significantly affect MeHg production, except in the high Hg treatment (i.e., HgH), due to minimal changes in the Hg fractions that regulate MeHg production. Furthermore, regardless of temperature changes, the relationship between GHGs and MeHg shifted from positive to negative as Hg levels increased. This highlights the need to balance carbon emission reduction and pollutant treatment policies to effectively reduce risks in contaminated sites. In conclusion, in terms of the current development of C management strategies for mitigating climate change and enhancing carbon sequestration, the turnover of SOM and its ecological implications for contaminated soils should be revisited. Future research should incorporate contaminated soils into global carbon models to improve SOM turnover predictions in terrestrial systems.