VESICULAR-ARBUSCULAR MYCORRHIZAS OF EQUISETUM SPECIES IN NORWAY AND THE USA - OCCURRENCE AND MYCOTROPHY

Typical vesicular-arbuscular mycorrhizal structures occurred in the sporophytes of Equisetum species (11 out of 12 species) collected in Norway and U.S.A. Plants growing in wet (hydric) habitats, sampled in the U.S.A. and Norway, had lower levels of colonization by vesicular-arbuscular mycorrhizal fungi than plants growing in mesic/dry-mesic habitats. Colonization levels ranged from 0 to 46% of the root length. Only E. variegatum found growing in a wet habitat in Illinois was consistently non-mycorrhizal. Equisetum species appear to be facultatively mycotrophic; the degree of mycotrophy may depend on habitat conditions. The world-wide warming and change from hydric to mesic conditions, during the late Carboniferous period and thereafter, probably contributed to the demise of the Equisetales. The demise of the Equisetales was less likely influenced by the, mycotrophic nature of higher plants, ferns, cycads and pines.