Relationship of soil fertility to suppression of the growth response of mycorrhizal big bluestem in non‐sterile soil

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Abstract
SUMMARY: When growth of vesicular‐arbuscular (VA) mycorrhizal and non‐mycorrhizal big bluestem was evaluated in 15 soils, three different growth response groups were evident. Group one, which included the prairie soils, displayed high mycorrhizal dependency as well as significant suppression of plant growth in non‐sterile soil. Group two showed no mycorrhizal dependency; however, plant growth was suppressed in nonsterile soil. The last group exhibited no mycorrhizal dependency or suppression in non‐sterile soil. Mycorrhizal dependency of big bluestem was not highly correlated with any individual soil parameter; however, concentrations of soil K, Ca, Cu, and Fe were used to successfully classify‘high’or‘low’mycorrhizal dependency. Suppression of plant growth in non‐sterile soil was also related to soil fertility. The magnitude of non‐sterile soil suppression was described by equations using soil Na, Zn, Mn, organic matter, Mg, and NH4. The mechanism of this suppression is still unclear; however, the nutrients which predict suppression may be related to the development of mycorrhizal symbosis or in demand by plants and other microbes, while those nutrients which predict mycorrhizal dependency may be related to those supplied to the plant by the symbiosis.