Combined XANES and Nanosims Analysis to Assess Spatial Patterns of Soil P Speciation from the Nano- to the Pedon Scale.

In recent years, it has become apparent that soil micro- and nano-structures highly determine the availability and allocation of phosphorus (P) in soils. Thus beside traditional wet-chemical methods, novel techniques that allow for the identification and quantification of P in different binding forms are needed to assess the importance of biogeochemical processes such as P transformation and storage in soils. Advanced techniques such as nano-scale Secondary Ion Mass Spectrometry (NanoSIMS) and synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy enable us to examine P in various intact soil structures from the nano- up to the pedon scale.

By comparison with reference compounds it is possible to unveil P speciation, a crucial parameter for P availability in soils, using XANES spectroscopy. Correla­ting the small scale spatial P distribution with the distribution of other elements like Fe, Al, Si or C obtained from NanoSIMS data enables also assumptions about the P speciation. Combination of both methods will allow an even more detailed in­sight into the distribution of P species at different spatial scales in soils.

We present data on the spatial distribution of different P forms in soils and soil aggregates from different forest sites in Germany which represent a gradient in P supply, from the nano- to the pedon scale. Results from cluster- and correlation analysis of NanoSIMS data, as well as results of linear combination fitting performed on XANES spectroscopy data are combined to determine P binding patterns in the investigated soils. Moreover, we discuss the capabilities and limitations of the used methods and the scale-dependency of the observed P distribution patterns.