Microbial biomass estimated by phospholipid phosphate in soils with diverse microbial communities

Phospholipid phosphate (PL-P) was tested as a measure of total microbial biomass in diverse soils with varying relative abundances of fungi. Phospholipid concentrations were compared with adenosine triphosphate (ATP), ergosterol, dehydrogenase activity, organic carbon and total N concentration. PL-P varied from 6 nmol g −1 in recently colonized dune sand to 1500 nmol g −1 in humus sieved from the pebbles of shingle ridge grassland. Meadow soils ranged from 340 nmol g −1 in arable land to 660 nmol g −1 in species-rich floodmeadow. Phospholipid phosphate correlated well with ATP ( r 2=0.80 or 0.93 minus one outlier, P < 0.001), total N ( r 2 =0.84, P < 0.001) and, negatively, with C:N ratio ( r 2 = 0.73, P < 0.001). The close relationship with N may reflect its limiting influence in sites that were mostly transitional stages within primary or old-field successions. A biomass conversion ratio of 419 ± 62 (SE) nmol PL-P mg −1 biomass C was estimated assuming 5.93 μg ATP mg −1 biomass C. Contrary to prediction, PL-P content of the microbial biomass did not fall with increasing fungal proportion; the PL-P: ATP molar ratio did not decrease with an increase in ergosterol: ATP molar ratio.