Soil samples were collected from the surface soil of three kinds of plantations mixed plantation of Dahurian larch and Manchurian ash, pure ash plantation and pure larch plantation, at Maoershan Forest experiment center in Heilongjiang Province. The result of measuring and analysis showed that the number of the bacteria was the most and their effective scope and active strength were the most remarkable comparing with various kinds of soil microorganisms. Actinomyces were the second most and the fungi were the least in number Numbers of the soil microorganisms in mixed plantation had a more number than that in the pure ash plantation. The number and species of microorganisms were different among different soil layers. For the same kind of soil, the number and species of the microorganisms in the surface layer were the most, and declined wth the increase of the soil depth. The seasonal change of the number of the soil microorganisms in pure or mixed pIantations was also remarkable. The number of the microorganisms increases obviously with the increase of the atmospheric temperature. The total number of microorganisms in Jan. was 30.0%-40.2% of the number in Sep. Both the vertical distribution and seasonal change being concerned, the number of the soil microorganisms in mixed plantation was on a higher level than that in pure plantation.
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