Nano-scale Secondary Ion Mass Spectrometry - Application to soil organic matter research

摘要

Many microbial-mediated processes exhibit high spatial variability across a wide range of scales (nm to cm) and at this scale very little is known about the spatial organization of soil particles, soil organic matter, plant roots and microorganisms and their interactions. Understanding the link between the heterogeneity of the soil's physical/chemical environment and its impact on biological processes is a major challenge in soil science. Nano-scale secondary ion mass spectrometry (NanoSEVIS) links ahigh resolution ion probe with isotopic analysis, which allows precise, spatially-explicit, elemental and isotopic analyses to be image mapped at the micro-scale (ca. 100 nm) (Herrmann et al. 2007a; 2007b). The power of NanoSEVIS lies in the ability ofthe instrument to distinguish stable isotopes of elements with a high sensitivity, i.e. concentrations of sub parts per million can be detected. Here we illustrate the potential of NanoSEVIS to examine plant root-bacterial and ectomycorrhizal competitionfor ~(15)N- and ~(13)C-labeled low molecular weight organic molecules. Amino acids are an important source of organic N for plants and C and N for microorganisms and as such these organic molecules are a major factor regulating ecosystem productivity. 15N- and 13C-labelled amino acids are often used to determine the relative competition between plants and microorganisms for dissolved organic matter. However, this has traditionally required bulk sample analysis (e.g. ground plant root material) which does not enable spatial resolution of the isotopes at a scale relevant to organic matter utilisation and competition by individual microbial and plant root cells.