Prolonged Storage of Bound Organic Carbon in Wetland but Not Upland Soils: A 13C and 14C Perspective

Abstract

Protection by metal (hydr) oxides is one of the key mechanisms for the long-term stabilization of soil organic carbon (SOC). However, the source and turnover of (metal-) bound organic carbon (OC) in soils are poorly constrained. Here we present the first large-scale study on the ¹³C and ¹⁴C characteristics of bound OC in 15 wetland and upland soil profiles. We find that bound OC has similar δ¹³C as SOC, suggesting no preference for plant- or microbe-derived carbon. However, bound OC Δ¹⁴C is more negative than SOC in wetland but not upland mineral soils, and decreases with increasing reactive minerals. Hence, in contrast to the conventional assumption, bound OC is better preserved relative to SOC in wetlands with high contents of reactive metals. Our finding highlights the dynamic exchange of bound OC with SOC in upland soils and calls for a better recognition of reactive metals in stabilizing OC in wetlands.