14C AMS as a tracer to study carbon dynamics resulting from paddy management under different climatic conditions in different soil types

BildPhase 1 of Research Unit 995, "Biogeochemistry of paddy soil evolution", showed a very fast replacement of carbon, originating from the parent material (estuarine sediments near Cixi, Zhejiang Province, China), with organic carbon derived from the recent atmosphere in paddy top soils; carbon replacement in non-paddy top soils was slower. Increasing 14C concentrations in the subsoil at constant or decreasing organic carbon (OC) documented the replacement of original estuarine OC by transport from above in both paddies and non-paddies, though at a slower pace under paddies. We hypothesize that measured concentration profiles in OC and 14C, found in paddy soils, represent snapshots of the dynamic balance between import of young carbon from above, its mineral stabilisation, and mineralisation and leaching. These carbon fluxes, in turn, depend on the input of fresh photosynthate, rainfall/irrigation, temperature, permeability of the plough pan (if any), soil microbes, soil mineral composition, and paddy management.