ARBUSCULAR MYCORRHIZAL ADAPTATION, SPORE GERMINATION, ROOT COLONIZATION, AND HOST-PLANT GROWTH AND MINERAL ACQUISITION AT LOW PH

Arbuscular mycorrhizal (AM) fungi colonize plant roots and often enhan ce host plant growth and mineral acquisition, particularly for plants grown under low nutrient and mineral stress conditions. Information ab out AM fungi and mycorrhizal (+AM) host plant responses at low pH(< 5) is limited. Acaulaspora are widely reported in acid soil, and Gigaspo ra sp, appear to be more common in acid soils than Glomus sp. Spores o f some AM fungi are more tolerant to acid conditions and high Al than others; Acaulospora sp., Gigaspora sp., and Glomus manihotis are parti cularly tolerant. Root colonization is generally less in low than in h igh pH soils. Percentage root colonization is generally not related to dry matter (DM) produced. Maximum enhancement of plant growth in acid soil varies with AM fungal isolate and soil pH, indicating adaptation of AM isolates to edaphic conditions. Acquisition of many mineral nut rients other than P and Zn is enhanced by +AM plants in acid soil, and the minerals whose concentration is enhanced are those commonly defic ient in acid soils (Ca, Mg, and K). Some AM fungal isolates are effect ive in overcoming soil acidity factors, especially Al toxicity, that r estrict plant growth at low pH.