SOIL MICROFLORA IN AN AREA WHERE SPRUCE (PICEA-ABIES) WAS KILLED BY SO2 EMISSIONS AND WAS SUCCEEDED BY BIRCH (BETULA-PENDULA) AND MOUNTAIN ASH (SORBUS-AUCUPARIA)

The spruce forests (Picea abies L. Karst.) in North Bohemia, Czech Rep ublic, died under the influence of SO, emissions. We observed (1988-19 89) that the number of heterotrophic soil bacteria decreased in the de composition horizons under the dead spruce trees, compared with the si tuation under healthy spruce forest. The number of micromycetes increa sed as a result of the influence of acid rain. The biochemical activit y of soil microbes was reduced. The breakdown of cellulose and the oxi dation of thiosulphate decreased as did respiration and ammonification . After the demise of spruce forests the groundflora developed and pio neer trees like birch (Betula pendula Rath.) and mountain ash (Sorbus aucuparia L.) took over. The grasses produced enormous amounts of exud ates and the leaf litter of new vegetation was well decomposed. There were ample nutrients for soil microflora. The microbial communities (b acteria plus micromycetes) increased greatly in organic soil horizons of stands with a grassground cover and mineralization of carbon and ni trogen compounds was more intensive there than under the dead spruce t rees. Decomposition and mineralization of the plant titter was also mo re intensive; the production of enzymes from the sulphur cycle increas ed in the bacterial component of microbial communities. The microflora of organic horizons increased under grass and after spruce had been r eplaced by birch and mountain ash.