Forest vegetation can accumulate the micronutrient manganese (Mn) in quantities that far exceed nutritional requirements. Manganese that accumulates in foliage is returned to the soil each year in litterfall where it may stimulate litter decomposition through microbially-mediated lignin oxidation. Although reactive Mn species have been proposed to drive oxidative decomposition of organic macromolecules in litter layers, the effects of Mn availability on organic matter transformation and storage during litter decomposition are poorly constrained. We tested interactive effects of Mn enrichment and warming on litter decomposition in an upland temperate forest in East Tennessee. Surface litter layers were enclosed in mesh bags and incubated on the soil surface for up to one year. Decomposing litter layers were either incubated under ambient temperatures or warmed +2-3°C and received between zero to 10 mg g<sup>-1</sup> monthly aqueous Mn(II) addition. Manganese and C K-edge x-ray absorption spectroscopies were used to evaluate changes in Mn oxidation state and dominant C functional groups during decomposition. While the initial litter layer contained primarily organic-bound Mn(II), decomposed organic matter was dominated by Mn(III/IV)-oxides. These changes corresponded to &gt;50% loss of initial Mn(II) combined with &gt;100% gain in Mn(III/IV)-oxides, indicating that Mn(II) was both leached and oxidized to form Mn-oxides during decomposition. Warming accelerated organic matter transformation but did not have clear effects on Mn speciation. Our results indicate that Mn(II) that is cycled through forest vegetation is rapidly oxidized during litter decomposition and likely contributes to patterns of Mn enrichment in shallow soils. These results are being coupled to measurements of lignin content and C fluxes in order to comprehensively evaluate interactions between Mn redox cycling and C storage in temperature forested soils.

Manganese redox transformation and associated organic matter degradation during leaf litter decomposition

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.