Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Xishuangbanna, Yunnan, 666303, China; Ailaoshan Station for Subtropical Forest Ecosystem Studies, Chinese Academy of Sciences, Jingdong, Yunnan, 676200, China.
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China.
Environ Pollut. 2021 Jan 1;268(Pt A):115867. doi: 10.1016/j.envpol.2020.115867. Epub 2020 Oct 27.
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 δHg and ΔHg both significantly correlate with δC and δN in soil profiles. Data analysis results show that microbial reduction is the dominant process for the distinct δHg shift (up to ∼1.0‰) between Oi and 0-10 cm surface mineral soil, and dark abiotic organic matter reduction is the main cause for the ΔHg shift (∼-0.18‰). Higher N in foliage leads to greater Hg concentration, and Hg 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.
凋落物汞（Hg）沉降是森林土壤 Hg 的主要来源。确定还原过程并追踪森林地表上的汞残留的命运是具有挑战性的任务。碳（C）和氮（N）同位素之间的相互作用可能会为 Hg 生物地球化学过程提供一些启示，因为它们的生物地球化学循环与有机物密切相关。在哀牢山常绿阔叶林地表的同位素测量显示，δHg 和 ΔHg 与土壤剖面中的 δC 和 δN 均呈显著相关。数据分析结果表明，微生物还原是 Oi 和 0-10 cm 表层矿质土壤之间明显的 δHg 偏移（高达约 1.0‰）的主要过程，而暗无生命的有机质还原是 ΔHg 偏移（约-0.18‰）的主要原因。叶片中较高的 N 导致 Hg 浓度增加，而通过微生物还原在地表重新释放 Hg 可能与 N 的释放和地表的固定有关。因此，我们认为全球森林生态系统中增强的 N 沉积可能会影响植被对 Hg 的吸收以及地表凋落物 Hg 的固定。
