Funding: DFG (German Research Foundation) within the Research Unit 995 (2008-2011)

Responsible researchers: Philipp Roth, Jan Siemens, Wulf Amelung, Zhihong Cao, Z.Y. Hu (State Key Laboratory of Soil and Sustainable Agriculture, CAS Chinese Academy of Sciences, Nanjing, P. R. China)

Rice is the world’s major crop, but it has low N utilization efficiency. This study is to contribute to a better understanding of present and past organic N cycles in paddy soils of the Yangtze Delta region in China. Soil samples will be collected from chronosequences of recent to ancient paddy soils (50 to 1000 years of rice cropping) and prehistoric ones (buried; several thousand years BP), each with adjacent unbroken wetland soils as references. We will use amino sugars and esp. amino acid enantiomers in combination with compoundspecific isotopic abundance measurements to elucidate the bacterial transformation and P3: Amelung and Brodowski 3 natural ageing of these hydrolysable soil organic N (SON) forms during paddy soil formation and preservation. In particular we aim at identifying (i) SON decomposition patterns within soil profiles, (ii) pools of different amino acid accumulation, and (iii) changes in the N biomarker signature in relation to the duration of rice cropping. The N-cycling using biomarkers is assessed (iv) in the short-term using the 13C content of soil amino acids after 13C pulse-labelling of rice plants, (v) in the medium-term by 14 tracing of bomb C in Dalanine and other amino acids, and (vi) in the long-term via the compound-specific 14C age of buried amino acid enantiomers.