Phosphorus is essential to maintaining primary productivity and is second only to nitrogen as the most limiting nutrient for plant growth. In the biosphere the cycling of C, N and P are inextricably linked with changes in one cycle impacting both directly and indirectly on the other cycles. Until relatively recently the importance of the soil biota in regulating these global environmental processes has been largely ignored due primarily to the difficulties in comprehending how processes operating at the nano- and micro-scales might impact at regional and planetary scales. However, developments in microbial ecology and in particular geomicrobiology are beginning to establish the importance of microbially mediated, enzyme catalysed reactions in the environment. This is mainly a result of the technological advances in genomics, proteomics and modelling that are now beginning to demonstrate how key biogeochemical cycles are regulated through complex interactions with the environments in which they operate.

For the C and N cycles much of this new information has come from the use of stable isotopes where the incorporation of isotopically labelled substrates into lipid and nucleic acid markers for microbial taxa or for functional groups has provided important insights into the cycling of these elements through the microbial community. For soils this offers the potential of at last opening the microbial ‘black box' with respect to C and N and complements biomass C and N studies done using techniques such as fumigation-extraction and fumigation-incubation. Whilst measures of biomass P and enzyme activity provide useful and important insights into the functioning of the P cycle in soils, they have not enabled the role of individual organisms or particular components of the community, such as fungi or bacteria to be determined. Thus, unlike carbon, where 13C-stable isotope labelling has been combined with molecular (rDNA-SIP, rRNA-SIP) and biochemical (incorporation into lipid biomarkers) probing to explore taxon specific transformations, molecular and chemical biomarker techniques have had limited impact on studies of the P cycle. This paper will address the current state of microbial cycling of P in soils and seek to identify future research needed to understand better the dynamics and regulation of microbially mediated P transformation in soils.