Lipid biogeochemistry of paddy soil evolution

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Subproject P7 investigates the molecular and isotopic composition of lipids in soils of different management systems, of different crop plants and of the corresponding substrates on which the soils evolved. Lipids chemotaxonomically differentiate the plant input into soil, identify plant combustion residues (PAH) that contribute to soil organic matter, and identify the microbial communities that thrive in soils of variable developmental stage. As the biogeochemistry of paddy soils depends on all of these control factors, lipid compositions are highly complementary to other approaches utilized in this project. The Fluvisol substrate composition in the coastal Cixi area and its lipid biogeochemistry has been characterized in detail in the first phase of FOR995. Extension and validation of these results via the study of different substrate types and associated effect on soil lipids will be conducted on Acrisols from China and Andosols, Vertisols and Acrisols/Ferralsols from Indonesia. Establishment of adapted microbial communities after conversion of marine tidal flats to paddy soils commenced in less than 50 years and thereafter remained rather stable for up to 2000 years in the Cixi area. An accelerated adaption to paddy management is hypothesized for the tropical environment in Indonesia, where a chronosequence with 110, 45 and 3 years of paddy use will be used to verify the postulated rapid changes in soil lipids. The management practices in Indonesia are expected to enforce longer periods of anoxia in paddies, affecting microbial activity and soil organic matter preservation. Environmental differences in paddy soil lipid geochemistry for the Cixi and Red Earth area in China, as well as for Java and Sumatera will be synthesized to obtain a general perspective of paddy soil evolution in Southeast Asia.