MICROBIAL BIOMASS PHOSPHORUS IN SOILS OF BEECH (FAGUS-SYLVATICA L) FORESTS

Thirty-eight soils from forest sites in central Germany dominated by beech trees (Fagus sylvatica L.) were sampled to a depth of about 10 cm after careful removal of the overlying organic layers. Microbial biomass P was estimated by the fumigation-extraction method, measuring the increase in NaHCO3-extractable phosphate. The size of the microbial P pool varied between 17.7 and 174.3 mu g P g(-1) soil and was on average more than seven times larger than NaHCO3-extractable phosphate. Microbial P was positively correlated with soil organic C and total P, reflecting the importance of soil organic matter as a P source. The mean microbial P concentration was 13.1% of total P, varying in most soils between 6 and 18. Microbial P and microbial C were significantly correlated with each other and had a mean ratio of 14.3. A wide (5.1-26.3) microbial C:P ratio indicates that there is no simple relationship between these two parameters. The microbial C:P ratio showed strong and positive correlations with soil pH and cation exchange capacity.