EFFECT OF IRRIGATION, FERTILIZATION, AND ARTIFICIAL DROUGHT ON BASIDIOMA PRODUCTION IN A NORWAY SPRUCE STAND

A total of 63 mycorrhizal and 49 saprotrophic species was found in a 30-year-old Picea abies stand in southwestern Sweden. Nitrogen addition had an obvious negative effect; all mycorrhizal species ceased to produce basidiomata in the 4th year of supply. Nitrogen-free fertilization resulted in reduced basidioma number and dry mass production by about 50% compared with the control. An increase in basidioma number was observed as result of irrigation, whereas the dry mass production was unaffected compared with the control. No fructification occurred, however, when nutrients were added together with the water. Artificial drought resulted in reduced basidioma production. The Ist year of recovery from drought resulted in an increase in basidioma number and biomass by a factor of 5 and 9 respectively, compared with the control. Production of Cortinarius species, Lactarius theiogalus, and Russula emetica increased as a result of irrigation, while a decrease was observed in Boletus edulis that instead was favoured by earlier drought. The saprotrophic species were only to a minor extent affected by the treatments. It is concluded that increased N deposition would result in decreased basidioma production and species number of mycorrhizal species and that changed precipitation climate would result in another species composition of mycorrhizal basidiomata in coniferous forests.