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Litterfall mercury (Hg) deposition is the dominant source of soil Hg in forests. Identifying reduction processes and tracking the fate of legacy Hg on forest floor are challenging tasks. Interplays between isotopes of carbon (C) and nitrogen (N) may shed some lights on Hg biogeochemical processes because their biogeochemical cycling closely links with organic matters. Isotope measurements at the evergreen broadleaf forest floor at Mt. Ailao (Mountain Ailao) display that delta Hg-202 and Delta Hg-199 both significantly correlate with delta C-13 and delta N-15 in soil profiles. Data analysis results show that microbial reduction is the dominant process for the distinct delta Hg-202 shift (up to similar to 1.0 parts per thousand) between Oi and 0-10 cm surface mineral soil, and dark abiotic organic matter reduction is the main cause for the Delta Hg-199 shift (similar to 0.18 parts per thousand). Higher N in foliage leads to greater Hg concentration, and Hg-0 re-emission via microbial reduction on forest floor is likely linked to N release and immobilization on forest floor. We thus suggest that the enhanced N deposition in global forest ecosystems can potentially influence Hg uptake by vegetation and litter Hg sequestration on forest floor. (C) 2020 Elsevier Ltd. All rights reserved.