14C AMS as a tracer to study carbon dynamics resulting from paddy management under different climatic conditions in different soil types
Final Report Abstract
The dynamic carbon cycling in agricultural top- and subsoil, found in Germany during the preceding DFG Priority Program 1090, is also seen in Zhejiang Province, China, and Jawa, Indonesia. - Most carbon cycling takes place on time scales of years to decades in the worked, accessible topsoil. Yet, carbon dynamics in the undisturbed subsoil, though involving only a few percent of the net primary production, may be more important for longer term carbon storage. - The 14C depletion of the deltaic parent material of the Chinese chronosequence was a surprise. It allowed us to demonstrate that the customary soil profile - 14C concentrations decreasing with increasing depth - can result from OM transport down into the subsoil instead of from sequential accumulation. - More detailed point sampling of soil layers reveals significant gradients in 14C (and OM) across the layers, befitting this downward transport of OM. Higher resolution sampling of soil profiles may thus provide the data needed to model and quantify OM transport and cycling in the subsoil. - Young root material in the deep subsoil demonstrates roots and exudates may provide young OM well below the normal root zone in the topsoil. - Concretions demonstrate the downward transport of iron and manganese from top- into subsoil caused by the alternate flooded (reducing) and dry (oxidizing) regime of rice paddies. The results from Jawa indicate groundwater may also induce redox cycles and concretion growth. - The single compound dating, planned together with partner projects, did not take place because (i) the Leibniz Laboratory experienced measuring problems in 2011/2012, (ii) the extensive blank testing needed to validate the purity of the compound isolation procedures could not be done due to (i), (iii) contact with the Leibniz Laboratory and access to an AMS system for research was broken in 2013. - Although our understanding of SOM has significantly improved, no simple way has yet been found to radiocarbon date a soil. This is because soils are “open systems” with carbon continuously cycling through and thus violate the primary closed system condition needed for radiocarbon dating.
Publications
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2013 .The carbon count of 2000 years of rice cultivation. Global Change Biology, 19, 1107–1113
Kalbitz, K., Kaiser, K., Fiedler, S., Kölbl, A., Amelung, W., Bräuer, T., Cao, Z., Don, A., Grootes, P., Jahn, R., Schwark, L., Vogelsang, V., Wissing, L., Kögel-Knabner, I.
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2013. Downward carbon transport in a 2000- year rice paddy soil chronosequence traced by radiocarbon measurements. Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, 294: 584 - 587
Bräuer, T., Grootes, P.M., Nadeau, M.-J., Andersen, N.
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2013. Origin of Subsoil Carbon in a Chinese Paddy Soil Chronosequence. Radiocarbon, 55(2-3): 1058-1070
Bräuer, T., Grootes, P.M. and Nadeau, M.J.
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2014. Organic carbon accumulation on soil mineral surfaces in paddy soils derived from tidal wetlands. Geoderma, 228: 90-103
Wissing, L., Kölbl, A., Schad, P., Bräuer, T., Cao, Z.H., Kögel-Knabner, I.
