Vertical distribution of microbial biomass in forest soils
Distribution of microbial biomass down soil profiles was studied in Scots pine (Pinus sylvestris) and oak (Quercus robur) stands located in southwestern Poland. Both microbial biomass concentration (mg Cmic g-1 soil) and content (kg Cmic ha-1), estimated by substrate-induced respiration (SIR) method, decreased exponentially down to the 60 cm of mineral soil and the function y = e-bx (y – a fraction of Cmic in x depth (cm) of that in the topsoil, b – coefficient of vertical distribution) gave a close fit to the obtained data. The values of coefficient b were found to be depended on the forest site type and were distinctly higher in oak stands, indicating more drastically decline of microbial biomass with depth of soil in deciduous than in coniferous forests. In pine forests considerable amounts of microbial biomass were located both in Ofh horizon (80-231 kg Cmic ha-1) and in 0–10 cm of mineral soil (35–60 kg Cmic ha-1), but significant amounts of Cmic were also found in deeper layers down to 40 cm. In oak stands most of microbial biomass was concentrated in the upper 10 cm of mineral soil (137–314 kg Cmic ha-1) and dramatically decreased in 10–20 cm layer to 23–48 Cmic ha-1. Due to a various vertical distribution of microbial biomass in forest soils, adjusting a sampling procedure to forest site types is necessary when assessing microbial characteristics. Soil samples for analyses should be taken from horizons of a high ecological relevance – in coniferous forests from the whole Ofh horizon and at least 0–10 cm layer of mineral soil, and in deciduous forests from the top 10 cm of mineral soil and possibly from organic layer when Ofh level is distinctly formed.
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