Microbial activities related to C and N cycling and microbial community structure in the rhizospheres of Pinus sylvestris, Picea abies and Betula pendula seedlings in an organic and mineral soil

The aim of this study was to determine whether Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karat.) and silver birch (Betula pend ula Roth) seedlings have a selective influence on the soil microbial commun ity structure and activity and whether this varies in different soils. Seed lings of pine, spruce and birch were planted into pots of two soil types. a n organic soil and a mineral soil. Pots without seedlings were also include d. After one growing season, microbial biomass C (C-mic) and N (N-mic), C m ineralization, net ammonification. net nitrification, denitrification poten tial, phospholipid fatty acid (PLFA) patterns and community level physiolog ical profiles (CLPPs) were measured in the rhizosphere soil of the seedling s. In the organic soil, C-mic and N-mic were higher in the birch rhizospher e than ill pine and spruce rhizosphere. The C mineralization rate was not a ffected by tree species. Unplanted soil contained the highest amount of min eral N and birch rhizosphere the lowest, but rates of net N mineralization and net nitrification did not differ between treatments. The microbial comm unity structure, measured by PLFAs, had changed in the rhizospheres of all tree species compared to the unplanted soil. Birch rhizosphere was most cle arly separated from the others. There was more of the fungal specific fatty acid 18:2 omega 6,9 and more branched fatty acids, common in Grain-positiv e bacteria, in this soil. CLPPs, done with Biolog GN plates and 30 addition al substrates, separated only birch rhizosphere from the others. In the min eral soil, roots of ail tree species stimulated C mineralization in soil an d prevented nitrification, but did not affect C-mic and N-mic, PLFA pattern s or CLPPs. The effects of different tree species did not vary in the miner al soil. Thus, in the mineral soil, the strongest effect on soil microbes w as the presence of a plant, regardless of the tree species, but in the orga nic soil, different tree species varied in their influence on soil microbes . (C) 1999 Federation of European Microbiological Societies. Published by E lsevier Science B.V. All rights reserved.