Comparison of Methods for Determining Microbial Biomass in Organo-Accumulative Mountainous Soils of the Caucasus

Microbial community plays an important role in biogeochemical processes in soil. There are many methods for studying the microbial biomass. However, the question arises about the most informative and suitable method for high-mountain soils. The objects of the study were organo-accumulative soils (Umbrisols) on north- and south-facing slopes in the subalpine and alpine zones at 1960, 2600, and 2940 m a.s.l. Four methods for estimating the microbial biomass carbon were used in this work: the method of determining soil phospholipids (C–PL), the method of substrate-induced respiration (C–SIR), the method of extracting double-stranded DNA (dsDNA) from soil (C–DNA), and the biokinetic method (C–BK). The C–DNA method gave underestimated results incomparable with the other three methods for the upper soil horizons. This was due to the known limitations of dsDNA isolation from organogenic soils. The results obtained by the C-SIR method were similar to those of the C–PLs method. The microbial biomass determined by the biokinetic method in the studied soils was maximum at all sites because of the predominance of fungal communities in the subalpine and alpine soils. More accurate values of microbial biomass in the upper horizons were obtained by the biokinetic method, while in the lower part of the profile more adequate estimates were obtained by the C–PL method.