TRACE-ELEMENT TOXICITY IN VA MYCORRHIZAL CUCUMBER GROWN ON WEATHERED COAL FLY-ASH

Mycorrhizal colonization is widely recognized as enhancing plant growt h on severely disturbed sites. A greenhouse pot experiment was conduct ed to determine if inoculation with vesicular-arbuscular mycorrhizal ( VAM) fungi will enhance vegetation establishment on abandoned coal fly ash basins. Spores of Glomus intraradices (Schenck and Smith) and Glo mus etunicatum (Becker and Gerdemann) were added to weathered precipit ator ash (EC = 0.91 dS m-1; pH 5.0) and to a pasteurized soil of the s ame pH (Grossarenic Paleudult, 92% sand, 1% organic matter). Some soil and ash were left unamended as non-mycorrhizal controls. Cucumber (Cu cumis sativus L. cv. Poinsette 76) seeds were sown, watered regularly, and fertilized periodically with macro-nutrient solution. By 8 weeks old, all ash-grown plants exhibited smaller leaves with leaf margin cu rl and necrosis, and plant biomass was significantly less (0.75x) than soil-grown plants. Based on analysis of 18 elements in plant tissues, toxicity to B, Mn or Zn could have caused growth suppression, confirm ing trace element problems for plant growth on fly ash. For plants gro wn on fly ash, G. etunicatum was the only fungus that colonized roots (20% of root length reduced from 67% on soil) and it suppressed plant growth to 0.80x that of uninoculated ash-grown plants. Correspondingly , shoot Zn concentration in G. etunicatum-inoculated plants was 3.5 x higher than in uninoculated plants and at generally toxic levels (273 mg kg-1). Glomus etunicatum had no other significant effects on elemen tal concentrations. These results indicate that VAM colonization in ac id, weathered fly ash suppressed plant growth by facilitating uptake o f Zn to toxic levels, and implies a limitation to successful use of VA M for vegetation establishment on abandoned coal fly ash basins.