The influence of phosphorus fertilization, drought, fungal species, and nonsterile soil on mycorrhizal growth response in tall grass prairie plants

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Abstract
In a series of experiments, factors effecting mycorrhizal growth response in prairie plants were examined. Two prairie grasses (Andropogon gerardii Vitman and Sorghastrum nutans (L.) Nash) and two forb species (Petalostemon purpureum (Venten) Rydb. and Liatris punctata Hook) benefited significantly from Glomus etunicatum Becker and Gerd. inoculation in fumigated or steamed soil. This benefit from mycorrhizae is probably related to phorphorus availability, since addition of 100 ppm phosphorus overcame the mycorrhizal growth response. No stimulation of growth occurred from additional vesicular-arbuscular, mycorrhizal inoculum to nonsterile soil. Neither was growth in nonsterile soil comparable to that achieved in inoculated, sterilized soil, suggesting a suppression of mycorrhizal growth response in nonsterile soil. In a related experiment addition of 1 or 10% nonsterile soil to sterilized, inoculated soil resulted in significantly reduced plant growth and greatly diminished mycorrhizal root colonization. Thus, soil microorganisms may suppress mycorrhizal growth responses, explaining the lack of mycorrhizal growth response observed in nonsterile soil. Of the four mycorrhizal fungi compared (Gigaspora rosea Nicol. and Schenk, Glomus deserticolum Trappe, Bloss and Menge, Glomus etunicatum Becker and Gerd., and Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe), the two indigenosu species most stimulated plant growth. Under severe moisture stress (-4500 kPa) a significant mycorrhizal growth response was evident for G. etunicatum, but not for G. deserticolum inoculated plants. Growth response does not necessarily suggest drought tolerance, since the magnitude of response was similar in adequately watered and severely droughted plants.
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