Assessment of mycorrhizal diversity in abandoned mine sites in Toledo, Cebu [Philippines] for bioremediation

A survey of mycorrhizal diversity associated with selected plant species within the 35,000-hectare Atlas Mines in Toledo, Cebu [Philippines], was conducted with the goal of rehabilitating abandoned copper mines through bioremediation by utilizing indigenous plants and mycorrhizal fungi. The Atlas Mine site is generally covered by vegetation classified as a disturbed grass-shrub-agroforest plant community. Plants growing in marginal and stressed environments similar to that in mine sites usually are associated with mycorrhizal fungi. Plants were identified and rhizosphere soil (including fine roots) were collected in five sites delineated by the mining company where ten samples were randomly collected from each site. Mycorrhizal colonization was assessed after the roots were cleared with potassium hydroxide and stained with tryphan blue. Mycorrhizal spores were separated from the soil using the wet sieving and decanting procedures and counted following the grid line intersect method. In the survey conducted, out of the 50 plants, only five (i.e. tycopodium, Saccharum spontaneum, Nephrolepis, Acacia mangium and Stachytarpheta jamaicensis) collected from two sites showed colonization by vesicular-arbuscular mycorrhizal (VAM) fungi, with infection ranging from 10-100%. All roots of Kandi-Kandilaan (Stachytarpheta jamaicensis) were colonized solely by Glomus sp. Kamachile (Pithecellobium dulce) harboured the highest spore density (2,575 spores/plant/30 g soil), consisting of Glomus, Cacaulospora and Entrophospora Datiles (Muntingia calabura), on the other hand, was the only plant associated with Glomus, Gigaspora, Scutellospora, Acaulospora and Entrophospora, but with low spore population. Glomus was the most prevalent among the VAM fungi. Fruit bodies of ectomycorrhizal (ECM) fungi: Pisolithus, Scleroderma, Thelephora and Bolettellus were found under Acacia auriculiformis, A. mangium, Eucalyptus urophylla and E. camaldulensis. Pisolithus was the most prevalent. These VAM and ECM fungi can be isolated and mass-produced as inoculants for the successful rehabilitation of mine sites. Nursery and field trials have shown that mycorrhizal fungi can enhance plant growth, promote survival in infertile and acidic soils and tolerance to heavy metals.