The influence of varied microbial substrate conditions on the growth and mycorrhizal colonization of little bluestem ( Schizachyrium scoparium (Michx.) Nash]

summary To determine the response of little bluestem [ Schizachyrlum scoparium (Michx.) Nash] to vesicular‐arbuscular mycorrhizal (VAM) fungi, various microbial populations, and interactions between VAM fungi and other microbes, plants were grown in three substrates: autoclaved soil, autoclaved soil to which VAM fungal‐free sievings of non‐autoclaved soil were added, and non‐autoclaved soil. Mycorrhizal plants were established in autoclaved soil and in autoclaved soil receiving sievings by using little bluestem root pieces that were Clorox‐treated for 9 or 17 s as a source of VAM fungal inoculum. Exposure of root pieces to a 0‐5 % solution of sodium hypochlorite (Clorox) for 13–23 s, surface‐sterilizes the roots, but it does not destroy viable internal VAM fungi. Control plants were grown in substrates receiving autoclaved root pieces. Plants grown in the autoclaved substrates had greater total biomass than plants grown in non‐autoclaved soil. Inoculum type (autoclaved or surface sterilized root pieces) or addition of sievings had no effect on any growth parameter for plants grown in autoclaved soil. Mycorrhizal plants grown in the autoclaved substrate, not receiving sievings had higher tissue concentrations of P, Ca, S, Zn, Mn, and Fe than non‐mycorrhizal plants grown in the same substrate. However, mycorrhizal plants did not produce more biomass than non‐mycorrhizal plants in autoclaved substrates. Differences observed between plants grown in the autoclaved and non‐autoclaved substrates are most likely attributable to greater nutrient availability of autoclaved substrates. The type of inoculum used and substrate conditions had negligible effects on rhizoplane and soil microbial populations. These included rhizoplane fungi and bacteria and selected functional groups of rhizoplane microbes (cellulose, chitin, and protein decomposers).