Abiotic nitrate incorporation, anaerobic microsites, and the ferrous wheel

Nitrate has long been thought to be chemically unreactive in soil. This view was challenged by the report of an apparently abiotic process whereby nitrate (NO₃ ^?) is incorporated into organic compounds (Dail et al. 2001). In Colman et al. (2007), we examined how common this process might be by testing for it in 45 soils collected from across a range of ecosystem types. We found no evidence of this process occurring in any of the soils, but found evidence of an analytical artifact that creates the appearance of incorporation. We suggested that prior evidence of this process might be due in part or in total to this analytical artifact. Davidson et al. (2008), however, challenged our results and conclusions, suggesting that we failed to observe the abiotic incorporation because we eliminated the anaerobic microsites they argue are necessary for the process. We address the criticisms, and show that they actually raise questions about the robustness of the only study to have reported abiotic NO₃ ^? incorporation in sterile soils. We argue that this area of research needs new artifact-free experiments if the controversy is going to be resolved.