Deep podzolized carbon: stabilization mechanisms for carbon accumulation in sandy soils.

Background/Question/Methods

The soils of the Southeastern Coastal Plain of the United States have been shown to harbor over one billion tons of terrestrial carbon one meter below the soil surface. This is surprising because sandy soils are generally thought to have low potential for carbon sequestration. Little is known about the mechanisms controlling its turnover, such as hydrology and chemical composition. These knowledge gaps will hinder any management efforts aimed at preserving this deep podzolized carbon and preventing its release into the atmosphere. To answer the question of how this carbon accumulated and why it has persisted in the soil, we characterized the bulk and dissolved carbon from three soil profiles, divided by horizon, via total organic carbon concentration and δ13C abundance. Water extractable organic matter was characterized by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Soils were also extracted using sodium pyrophosphate to estimate organic complexed metals and assess the relative importance of metal protection and hydrology to the stabilization of this carbon.

Results/Conclusions

Preliminary results show that the amount of dissolved organic carbon (DOC) contained within horizons of deep podzolized carbon surpasses DOC of samples from surface horizons. We find that a significant fraction of the total organic carbon was in the form of organic-metal complexes which were extractable by sodium pyrophosphate solution. C:N ratios for deep podzolized carbon are between 20 to 80, which is significantly higher than surface soil and is indicative of material that has not been extensively processed by microbial activities. These results suggest that the deep podzolized carbon is primarily stabilized by metal associations which confer a degree of protection against microbial decomposition.