Soil pH-induced changes in root colonization, diversity, and reproduction of symbiotic arbuscular mycorrhizal fungi from healthy and declining maple forests

Acer saccharum Marsh. (sugar maple) is one of only few arbuscular mycorrhiz al trees to form extensive stands in northern temperate biomes. Recent mapl e decline could result from altered intensity and quality of root colonizat ion by associated mycobionts or possible shifts in symbiotic fungal communi ty composition following environmental stresses. In this study the effects on arbuscular mycorrhizal fungi of soil acidification, one of several propo sed causal stresses underlying forest decline, and remedial liming were inv estigated under glasshouse conditions. Acer saccharum seedlings were grown in unsterilized, pH altered, forest soils from healthy and declining maple stands. Over a range of treatment pHs normally tolerated by A. saccharum, f ungal populations and responses to pH changes differed between the two soil s. The declining site with more acidic soil had an initially larger spore p opulation but lower taxonomic diversity than the healthy site. However, lim ing stimulated sporulation of several taxa initially apparently absent from the declining site spore population. The quantity of colonization generall y increased with pH for both sites. Five Glomus taxa and Scutellospora calo spora (Nicol. & Gerd.) Walker & Sanders are added to the list of fungi know n to form arbuscular mycorrhizas with A. saccharum, and the known range of Acaulospora cavernata Blaszkowski is extended from Poland to eastern North America.