Linking Phosphorus Forms to Soil Microbes Through FAME and P-NMR Spectroscopy.

Microbes can be both a source and sink for phosphorus (P) in soils. However, there is little information available about the specific P forms produced by soil microbial populations or the factors controlling the cycling of microbial P.  For this study, our objective was to trace the flow and fate of added P, and how different microbial communities partition P when it is limiting, or in excess. We used soils from a Hawaiian chronosequence to examine microbial utilization of P in high and low P mixed lab cultures. Soils from 2 sites, one high in P (fertile) and one low in P (P-limited), were used to inoculate high and low P media.  Cultures were sampled 0, 1, 2, 4, and 7 days after inoculation.  Samples were collected to measure 1) 3 P enzymes: acid phosphomonoesterase, alkaline phosphomonoesterase and diesterase; 2) ³¹P-NMR (cells and supernatant); 3) microbial community composition, biomass (FAME), and  4) total P, C and N. Results show differing microbial response to the high and low P in the medium.  For example, the community from the P-limited soil, in the low P medium, was dominated by fungi, while the community from the fertile soil was dominated by bacteria.  Activities of all three enzymes increased over time, and varied by soil and P treatment.  Acid phosphomonoesterase activity differed by soil, with higher activity from the P-limited soil.  Diesterase activity differed by P treatment, with more activity in the low P medium, regardless of soil. Phosphorus forms changed from only orthophosphate at the start to a range of orthophosphate monoesters and diesters at the end of the experiment.