Diversity of arbuscular mycorrhizal fungi on an acidic mine site

On abandoned coalmines in regions of the eastern United States, extreme soil acidity and aluminum (Al) toxicity play a significant role in limiting site re-vegetation. Primary succession on these sites is led by broomsedge (Andropogon virginicus). However, broomsedge is not Al resistant, but relies on symbiotic arbuscular mycorrhizal fungi (AMF) to confer Al resistance. A wide degree in functional variation in Al resistance exists among AMF isolates and species, even among those collected from acidic soils, suggesting that complex interactions function during re-vegetation that may protect both the plant host and AMF community from Al. We investigated patterns of AMF species diversity across a vegetation gradient on an abandoned mine. Soils were sampled along a re-vegetation sequence from bare soil, vegetation island edge, grass sward-island, to developed woody vegetation-island. Soil Al and AMF spore abundance and speciation were assessed. AMF were cultured in vegetation traps to identify AMF that may not have been sporulating in the field. Soil total Al dropped from 0.36 µmol/g in bare soil to 0.062 µmol/g in the interior of vegetated islands. Free (phytotoxic) Al species represented 71% of the available Al in bare soils and 5% in vegetated samples. Along this gradient, soil AMF spore abundance increased from bare soil (5 spores/50 mL) to their greatest in the sward-islands (8,076 spores/50 mL). Species presence increased from bare (3) to woody (6), whereas diversity was greatest at edges and in woody plots. There were no species characteristic of Al dominated soils, although Acaulospora morrowiae and Glomus diaphanum were not present in edge or bare soil samples. Specific AMF may facilitate the colonization of bare soils and other AMF species may then become established as the island vegetation provides habitat for a more diverse mycorrhizal community.