Characterizing the Atmospheric Mn Cycle and Its Impact on Terrestrial
Biogeochemistry
Abstract
Manganese (Mn) is a key cofactor in enzymes responsible for lignin decay
(mainly Mn peroxidase), regulating the rate of litter degradation and
carbon (C) turnover in temperate and boreal forest biomes.While soil Mn
is mainly derived from bedrock, atmospheric Mn could also contribute to
soil Mn cycling, especially within the surficial horizon, with
implications for soil C cycling. However, quantification of the
atmospheric Mn cycle, which comprises emissions from natural (desert
dust, sea salts, volcanoes, primary biogenic particles, and wildfires)
and anthropogenic sources (e.g. industrialization and land-use change
due to agriculture) transport, and deposition into the terrestrial and
marine ecosystem, remains uncertain. Here, we use compiled emission
datasets for each identified source to model and quantify the
atmospheric Mn cycle with observational constraints. We estimated global
emissions of atmospheric Mn in aerosols (<10 µm in aerodynamic
diameter) to be 1500 Gg Mn yr-1. Approximately 32% of the emissions
come from anthropogenic sources. Deposition of the anthropogenic Mn
shortened soil Mn “pseudo” turnover times in surficial soils about 1-m
depth (ranging from 1,000 to over 10,000,000 years) by 1-2 orders of
magnitude in industrialized regions. Such anthropogenic Mn inputs
boosted the Mn-to-N ratio of the atmospheric deposition in non-desert
dominated regions (between 5×10-5 and 0.02) across industrialized areas,
but still lower than soil Mn-to-N ratio by 1-3 orders of magnitude.
Correlation analysis revealed a negative relationship between Mn
deposition and topsoil C density across temperate and (sub)tropical
forests, illuminating the role of Mn deposition in these ecosystems.