Structure of the microbial communities in coniferous forest soils in relation to site fertility and stand development stage

The structure, biomass, and activity of the microbial community in the humu s layer of boreal coniferous forest stands of different fertility were stud ied. The Scots pine dominated CT (Calluna vulgaris type) represented the lo west fertility, while VT (Vaccinium vitis-idaea type), MT (Vaccinium myrtil lus type), and OMT (Oxalis acetocella-Vaccinium myrtillus type) following t his order, were more fertile types. The microbial community was studied mor e closely by sampling a succession gradient (from a treeless area to a 180- years-old Norway spruce stand) at the MT type site. The phospholipid fatty acid (PLFA) analysis revealed a gradual shift in the structure of the micro bial community along the fertility gradient even though the total microbial biomass and respiration rate remained unchanged. The relative abundance of fungi decreased and that of bacteria increased with increasing fertility. The structure of the bacterial community also changed along the fertility g radient. Irrespective of a decrease in fungal biomass and change in bacteri al community structure after clear-cutting, the PLFA analysis did not show strong differences in the microbial communities in the stands of different age growing on the MT type site. The spatial variation in the structure of the microbial community was studied at a MT type site. Semivariograms indic ated that the bacterial biomass, the ratio between the fungal and bacterial biomasses, and the relative amount of PLFA 16:1 omega 5 were spatially aut ocorrelated within distances around 3 to 4 m. The total microbial and funga l biomasses were autocorrelated only up to 1 m. The spatial distribution of the humus microbial community was correlated mainly with the location of t he trees, and consequently, with the forest floor vegetation.