Comparison of bacterial and fungal biomass determined by phospholipid fatty acid and direct microscopical analysis in 4 types of upland soils

Abstract

We investigated the relationship between the phospholipid fatty acid (PLFA) content and bacterial and fungal biomass in soils incubated in the presence/ absence of cellulose or glucose. PLFA content except for 18 : 2ω6 in soil was correlated with the bacterial biomass estimated by direct bacterial counts (r =0.75 ; p< 0.01, n=66) and the average ratio of bacterial biomass to PLFA content was 4.7±0.2 in 3 types of upland soils. These results suggest that the bacterial biomass can be estimated based on the PLFA content in soil. A positive correlation (r=0.50 ; P<0.01, n=86) was also found between the content of PLFA 18 : 2ω6 and the fungal biomass determined by direct microscopical analysis in 4 types of upland soils. This correlation coefficient increased when the soils containing PLFA 18 : 2ω6 below 0.1 mg g^<-1> dry soil were omitted (r=0.64 ; p<0.01, n=38). In this case, the average ratio of fungal biomass to PLFA 18 : 2ω6 content was 822±71. A similar average ratio was observed in a Low Humic Andosol after application of pig compost (769±149). These results suggest that the PLFA 18 : 2ω6 content could be used to estimate the fungal biomass in soils containing PLFA 18 : 2ω6 above 0.1 mg g^<-1> dry soil. The content of PLFA 18 : 2ω6 increased about three times more than did the fungal biomass just after application of pig compost. In such cases, the PLFA 18 : 2ω6 content could be a relative measure of fungal biomass.