The fate of mercury and its relationship with carbon, nitrogen and bacterial communities during litter decomposing in two subtropical forests

Forests play a significant role in the biogeochemical cycling of mercury (Hg). Litterfall represent a dominant pathway for Hg to reach the ground surface under a forest canopy. In order to understand Hg accumulation in the litterfall, the dynamics of Hg, carbon (C), nitrogen (N), microbial C and N, as well as bacterial community in the decaying litterfall of two typical subtropical forest stands in southwest China were investigated for one year. THg levels in the litterfall after one-year increased to 124.64% and 135.90%, and MeHg levels in the litterfall increased up to 295.65% and 209.38% of the initial values in the mixed broadleaf-conifer forest and evergreen broadleaf forest respectively. Differently, the concentrations of THg and MeHg in the organic layer of the underlying soil were quite stable. The concentrations of THg in the decaying litterfall corresponded negatively with C/N ratios. Bacterial community analysis found that the bacteria previously being confirmed as Hg methylators did not occur in the genera of the decomposing litterfall in the two forest stands, which might imply that the increase of MeHg during decomposing did not mainly due to the contribution of confirmed Hg methylators, and other sources of MeHg might exert certain roles. (C) 2017 Elsevier Ltd. All rights reserved.