Uptake and transport of phosphorus by Agrostis capillaris seedlings from rapidly hydrolysed organic sources extracted from32 P-labelled bacterial cultures

Cultures of the soil bacterium Serratia liquifaciens grimesii were grown with³² P labelled phosphate, to produce a uniformly³² P labelled source of microbial P. Extracts of the bacteria were prepared by sonication, dialysis and filtration to provide a clear sterile solution which was characterised in terms of dissolved organic and condensed P (DOP and DCP) and molecular weight range. The extract was used as a source of P to Agrostis capillaris L. seedlings in nutrient solution from which orthophosphate was omitted. In a time course experiment, root surface phosphatase activity increased as soon as extract was added to the root medium, DOP was rapidly hydrolysed and orthophosphate concentration increased rapidly. These processes were complete within about 8 h, after which phosphatase activity fell to its original level, and the plants absorbed molybdate reactive P from the nutrient solution so that it reached its original concentration over 48 h. DCP concentrations did not change significantly throughout the experiment. This work clearly demonstrated that DOP but not DCP, as a component of a bacterial extract produced by a relatively straightforward method, was quickly hydrolysed and the P made available for plant uptake.