Carbon Storage and DNA Adsorption in Allophanic Soils and Paleosols
Andisols and andic paleosols dominated by the nanocrystalline mineral allophane sequester large amounts of carbon (C), attributable mainly to its chemical bonding with charged hydroxyl groups on the surface of allophane together with its physical protection in nanopores within and between allophane nanoaggregates. C near-edge X-ray absorption fine structure (NEXAFS) spectra for a New Zealand Andisol (Tirau series) showed that the organic matter (OM) mainly comprises quinonic, aromatic, aliphatic, and carboxylic C. In different buried horizons from several other Andisols, C contents varied but the C species were similar, attributable to pedogenic processes operating during developmental upbuilding, downward leaching, or both. The presence of OM in natural allophanic soils weakened the adsorption of DNA on clay; an adsorption isotherm experiment involving humic acid (HA) showed that HA-free synthetic allophane adsorbed seven times more DNA than HA-rich synthetic allophane. Phosphorus X-ray absorption near-edge structure (XANES) spectra for salmon-sperm DNA and DNA-clay complexes indicated that DNA was bound to the allophane clay through the phosphate group, but it is not clear if DNA was chemically bound to the surface of the allophane or to OM, or both. We plan more experiments to investigate interactions among DNA, allophane (natural and synthetic), and OM. Because DNA shows a high affinity to allophane, we are studying the potential to reconstruct late Quaternary palaeoenvironments by attempting to extract and characterise ancient DNA from allophanic paleosols.
KeywordsAndisols Allophane Carbon sequestration C NEXAFS P XANES Ancient DNA
This research was supported by the Marsden Fund (10-UOW-056) through the Royal Society of New Zealand. We thank NSRRC, Taiwan, and especially Dr. Tsan-Yao Chen for technical instruction and support, Ling-Yun Jang for P XANES spectra for salmon-sperm DNA, Prof Shin-Ichiro Wada (Kyushu University) for advice on allophane synthesis, Dr. Emma Summers, Janine Ryburn, and Lynne Parker (Waikato University) for help with experiments, and Prof Kevin McSweeney (University of Wisconsin—Madison) for reviewing the paper.
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