Effects of repeated harvesting of forest residues on the ectomycorrhizal community in a Swedish spruce forest

The use of biofuels has been proposed as one possible substitute for fossil fuels, which contribute substantially to the increase in [CO2] in the atmo sphere. However, increased harvesting of forest residues for biofuel might affect the availability of base cations, P and N, as well as the developmen t, community dynamics and function of ectomycorrhizas. This in turn might i nfluence nutrient uptake and tree growth. In this study we investigated the effects of repeated forest residue harvesting on ectomycorrhizal species c olonizing spruce roots in the humus layer of a 35-yr-old forest. Harvesting significantly decreased the thickness of the humus layer as well as decrea sing the numbers of ectomycorrhizal root tips both per metre root length an d per unit humus volume. Changes in mycorrhizal community structure were st udied by ITS typing with the use of PCR-RFLP analysis. In total, 19 differe nt ITS types were found on two different sampling occasions (autumn and spr ing); 11 of these were common to both samplings. Nine of the ITS types were identified to at least the genus level by comparison with RFLP patterns of identified fruiting bodies or axenic cultures. Five species, Cortinarius s p. 2, Thelephora terrestris (Ehrenb.) Fr., Lactarius theiogalus (Bull.:Fr.) S. F. Gray s.st. Neuhoff, Tylospora fibrillosa Donk and To-96-12, occurred on over 5% of the total sampled root tips. Together these five types colon ized 63% of the mycorrhizas screened. A similarity index assessment showed no shift in mycorrhizal community structure as a result of harvesting. Our findings suggest that the repeated removal of forest residues might have a strong effect on the quantity and development of ectomycorrhizal roots in t he organic horizon, but little effect on the species composition of the com munity.