Dissipation of bacterially derived C and N through the meso- and macrofauna of a grassland soil

Feeding relationships between organisms may be determined by observations of behaviour in manipulative experiments or, as in more recent times, by the use of stable isotope labelling to trace the passage of 13C and 15N through food webs. Here we introduce living bacteria, labelled with both 13C and 15N into intact soil cores to understand further the movement of bacterially sourced C and N into the meso- and macrofauna of a grassland soil. We found that these groups showed a range of isotope levels which relate to their feeding strategies. Some had no label (e.g. dipterous larvae), whilst others were highly labelled which may indicate a preference for the added bacteria. This latter group included Collembola, generally perceived as being predominantly fungal feeders. This work describes a novel technique which has the potential to provide critical information about the dissipation of bacterially derived C and N through the soil food web.