Variation in Vesicular-Arbuscular Mycorrhizal Relationships of Two Sand Prairie Species

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Abstract
We tested the hypothesis that western sunflower (Helianthus occidentalis) reduces abundance of prairie species within its colonies by producing allelochemics that inhibit seed germination or vesicular-arbuscular mycorrhizal (VAM) formation. Germination of seeds of prairie species was not significantly (P < 0.05) inhibited by water extracts of whole sunflower plants or soil collected inside the colony. Comparisons were made of VAM inoculum potential between soil collected from within a sunflower colony and an adjacent area outside the colony dominated by sand lovegrass (Eragrostis trichodes). Significant differences in VAM inoculum potential were found due to season but not due to site of collection. Sunflower roots were significantly more colonized (75 vs. 34%) and more infectious in bioassay tests than lovegrass roots. Root mass (mg/cc) was significantly greater outside the colony than inside, possibly accounting for similarity in inoculum potential between the two areas. Differences in VAM colonization levels and infectivity between sunflower and lovegrass suggest different mycorrhizal relationships for these tap- and fibrous-rooted species, respectively.