title: Long-term litter decomposition controlled by manganese redox cycling.
abstract: Litter decomposition is a keystone ecosystem process impacting nutrient cycling and productivity, soil properties, and the terrestrial carbon (C) balance, but the factors regulating decomposition rate are still poorly understood. Traditional models assume that the rate is controlled by litter quality, relying on parameters such as lignin content as predictors. However, a strong correlation has been observed between the manganese (Mn) content of litter and decomposition rates across a variety of forest ecosystems. Here, we show that long-term litter decomposition in forest ecosystems is tightly coupled to Mn redox cycling. Over 7 years of litter decomposition, microbial transformation of litter was paralleled by variations in Mn oxidation state and concentration. A detailed chemical imaging analysis of the litter revealed that fungi recruit and redistribute unreactive Mn(2+) provided by fresh plant litter to produce oxidative Mn(3+) species at sites of active decay, with Mn eventually accumulating as insoluble Mn(3+/4+) oxides. Formation of reactive Mn(3+) species coincided with the generation of aromatic oxidation products, providing direct proof of the previously posited role of Mn(3+)-based oxidizers in the breakdown of litter. Our results suggest that the litter-decomposing machinery at our coniferous forest site depends on the ability of plants and microbes to supply, accumulate, and regenerate short-lived Mn(3+) species in the litter layer. This observation indicates that biogeochemical constraints on bioavailability, mobility, and reactivity of Mn in the plant-soil system may have a profound impact on litter decomposition rates.
authors.affiliation: Soils Division, Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97330; Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550; keiluweit@umass.edu.
authors.forename: Marco
authors.initials: M
authors.lastname: Keiluweit
authors.affiliation: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
authors.forename: Peter
authors.initials: P
authors.lastname: Nico
authors.affiliation: Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331;
authors.forename: Mark E
authors.initials: ME
authors.lastname: Harmon
authors.affiliation: Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529;
authors.forename: Jingdong
authors.initials: J
authors.lastname: Mao
authors.affiliation: Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550;
authors.forename: Jennifer
authors.initials: J
authors.lastname: Pett-Ridge
authors.affiliation: Soils Division, Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97330; Institut für Bodenlandschaftsforschung, Leibnitz-Zentrum für Agrarlandschaftsforschung (ZALF), 15374 Muuncheberg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Kleber
mesh_terms: D002244:Carbon / Q000737:chemistry; D057231:Climate Change; D017753:Ecosystem; D065928:Forests; D008031:Lignin / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D018515:Plant Leaves / Q000378:metabolism; D010944:Plants; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D017356:Synchrotrons; D013997:Time Factors
chemical_list: D012987:Soil; D008345:Manganese; D002244:Carbon; D008031:Lignin; D010100:Oxygen
keywords: climate change; forest soil ecosystems; nutrient cycling; soil-atmosphere interactions; terrestrial carbon cycle