The effects of forestry practices on ectomycorrhizal fungal communities and seedling establishment Integrated studies on biodiversity, podzol profile, clear-cut logging impacts and seedling inoculation

Ectomycorrhizal fungi form symbioses with all the major tree species in the boreal forest zone and they are of key importance in nutrient acquisition, plant protection against root pathogens and drought stress. Their diversity and the impacts of forestry practises on these highly important organisms is therefore of great interest. The aim of the study was to describe ectomycorrhizal biodiversity in boreal forest soils, and to determine biodiversity responses to different forestry practises. A specific focus was on the carbon allocation, bacterial carbon source utilization and vertical ectomycorrhizal species distribution in the podzol profile. Additionally, inoculation performance of certain, selected ectomycorrhizal fungal isolates obtained from the microcosm and field experiments was tested, and the performance and community-level influence of inoculated ectomycorrhizal fungal and mycorrhizal helper bacterial strains, a combination which is already in commercial use in France, was also investigated under field conditions. Three microcosm experiments, one combined tube and pot experiment and two field experiments were accomplished. All experiments were performed in a Scots pine forest in southern Finland, or using soil collected from that forest, except the second field experiment, which was carried out in the Vosges region in France. Radiolabelled CO2 was used in the carbon allocation study; Biolog microtitre plates were used in the bacterial carbon source utilization experiments; and gross morphotyping following PCRRFLP fingerprinting and sequencing were used in all the studies dealing with ectomycorrhizal identification. Photosynthetically fixed carbon was shown to be equally distributed in roots and mycorrhizas in humus, Eand B-horizons suggesting that roots and ectomycorrhizal fungi significantly support biological activity in podzol horizons. The data also support theories of the important roles of ectomycorrhizal fungi in podzolization and weathering processes. Congruently, bacterial communities associated with roots and ectomycorrhizas utilised a wide range of carbon souces, measured using CLPP (community level physiological profiling) analysis, suggesting their active role in Eand B-mineral horizons. Root-associated ectomycorrhizal fungal communities of the seedlings growing in the field and microcosms were diverse: in total, 53 taxa were determined. Shifts in community structure occured after clear-cut logging and podzol horizon-specific species were identified. Four taxa (representing in most cases a single fungal species) were dominant in the field, namely an unknown Piloderma sp., Suillus variegatus, Phialocephala fortinii-aggregate and Cenococcum geophilum. Based on the field experiment, it is concluded that the shift in ectomycorrhizal community structure observed in the seedling roots after clear-cut logging is not due to the lack of inoculum in the clear-cut soil but due to changes in the soil environment. It was shown both in tube and pot experiments using Finnish forest isolates, and in the French field experiment using well-studied fungal and bacterial strains, that seedling inoculation with ectomycorrhizal fungi can have a positive impact on seedling growth even though no detectable differences in indigenous bacterial and fungal communities can be found. Gross morphotyping following PCR-RFLP fingerprinting and sequencing was shown to be a suitable method for forest-scale ectomycorrhizal biodiversity studies. Ectomycorrhizal fungal diversity detected in microcosm experiments was shown to mimic relatively well the diversity observed in the field experiment, although most of the rare species identified in the field experiment were not found in the laboratory conditions.