Prevalence and Contribution of Anaerobic Microsites to Carbon Mineralization in Upland Soils

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Scott E Fendorf1, Marco Keiluweit1, Kaitlyn Elizabeth Gee1, Markus Kleber2, Thomas Wanzek2 and Peter S Nico3, (1)Stanford University, Stanford, CA, United States, (2)Oregon State University, Corvallis, OR, United States, (3)Lawrence Berkeley National Laboratory, Berkeley, CA, United States
Soil organic matter (SOM) storage, or residence time, is dominantly controlled by the mineralization (oxidation) rate, which is affected by climatic factors (particularly temperature and rainfall) influencing microbial metabolic rates as well as SOM chemistry, mineral-organic associations, and physical protection. Variation in anaerobic respiratory pathways can further, and dramatically, impact carbon oxidation rates. Within the aggregated structure of soils, steep chemical gradients arise from the supply of oxygen and nutrients along macropores that are rapidly consumed (relative to supply) within the micropore domains of aggregate interiors. As a consequence of demand exceeding oxygen supply within soil aggregates and peds, an appreciable fraction of the soil volume may persist in an anaerobic state within upland, agriculturally productive system. Factors limiting oxygen diffusion and availability such as soil texture, soil moisture content, organic matter input, and aggregate size (soil structure) provide central controls on microbial carbon mineralization rates. Here, we combine laboratory studies with manipulations of field samples and in-field measurements to illustrate how soil structure and carbon availability interact to impose anaerobic conditions and associated respiratory constraints on organic matter mineralization rates and thus storage within soils.