Succession of arbuscular mycorrhizal communities in the foreland of the retreating Morteratsch glacier in the Central Alps

The development of communities of arbuscular mycorrhizal fungi (AMF) was investigated in the sub-alpine foreland of the glacier Morteratsch located at approx. 1900-2100 m a.s.l. near Pontresina (Engiadin' Ota, Switzerland). In particular, we asked if the succession of AMF communities follows or precedes the primary plant succession, and we checked the mycorrhizal status of the pioneer plant Epilobium fleischeri. Soil samples were taken at pioneer and dense grassland sites established during the last hundred years representing different periods of glacier retreat: 1875-1900,1940-1950,1970-1980 and 1990-2000. Extraradical hyphal length densities and AMF spore populations were analyzed in soil samples. Spore formation and mycorrhizal root colonization were monitored in trap cultures grown on Trifolium pratense, Lolium perenne, Plantago lanceolata and Hieracium pilosella or on E. fleischeri over 14 months. We found that E. fleischeri is strongly arbuscular mycorrhizal, but plants in closest distance to the glacier (glacier retreat in the last 4-6 years before sampling) were non-mycorrhizal. Spore densities and root colonization in trap cultures were generally low in samples from glacier stage 1990-2000. Highest spore density and colonization were found for the sites ice-free since 1970-1980, whilst highest AMF species richness and hyphal length densities were found at the sites ice-free since 1875-1900. Our findings show an establishment of a few AMF pioneer species (e.g. Diversispora versiformis and Acaulospora punctata) within 5-10 years and species rich AM F communities at sites ice-free for 100 years (28 species). Their succession generally follows the succession of the plant communities. We conclude that AMF pioneer species might be mainly distributed by wind transport while other AMF fungi (e.g. Glomus rub:forme and Glomus aureum) rather need a below-ground hyphal network to invade new areas. (C) 2011 Elsevier GmbH. All rights reserved.