Recent research has suggested that root/belowground organic matter (OM) is a more likely and important source of soil OM than is shoot/aboveground OM. Carbon and nitrogen isotopes have traditionally been used to study OM cycling in soils, even though above- and below- ground OM pools are not always isotopically distinct. Stable isotope ratios of hydrogen (δ2H) in roots and soil OM have recently been shown to provide an additional tracer for soil OM cycling (Ruppenthal et al., 2015). The δ2H values of roots are not influenced significantly by evaporative transpiration and therefore are more closely correlated to climate and precipitation δ2H values as compared to shoot OM. We found that the δ2H values of roots from near the surface were more negative by 8-40‰ relative to the δ2H values of fresh leaf tissues and surface litter. In soils, we combined physical density separation and isotopic (δ2H, δ13C, δ15N) analyses to understand how root-derived OM contributes to the OM stored in soils. The δ2H and δ13C of soil OM from 1) free, 2) occluded, and/or 3) mineral associated soil fractions in upper soil horizons (up to 1 m) will be presented and compared from a suite of soils collected from a CZO (Critical Zone Observatory) climosequence in the southern Sierra Nevada range (USA). Whether or not the δ2H of these soil fractions relates to climate and precipitation patterns will also be discussed.
Fogel, M., Berhe, A., Williams, E. (2015): Can δ2H of Organic Matter in Soils be Used for Understanding Organic Matter Sources and Cycling?. B33D Soil Organic Matter: Mechanisms of Stabilization and Change II Posters, presented at 2015 Fall Meeting, AGU, San Francisco, CA, 14-18 Dec..