Mycorrhizal influences on big bluestem rhizome regrowth and clipping tolerance

Mycorrbizal symbiosis is critical to growth of many warmseason prairie grass seedlings, but its effect on regrowth of rbizomes has not been determined. As forage species, the effect of grazing on the symbiosis is also important. when the impact of mycorrbizae on regrowth of Andropogon germ&i Vit. rhizomes was assessed, A. germ& rhizomes collected from the field and grown with mycorrbizal inoculum produced larger plants than rhizomes grown in the absence of the symbiont. The effect of the symbiosis on clipping (simulated grazing) tolerance was quantified by growing A. germdiiin steamed or nonsterile prairie soil, with or without mycorrbizal fungus inoculation. Plants were clipped and a portion of the plants harvested at 6,12,18,24, and 30 weeks after planting. As an additional control, Benomyl fungicide was applied to plants to inhibit the symbiosis. Mycorrhiul clipped plants were larger than nonmycorrbizal clipped plants, but the difference diminished with successive clippings. Mycorrbizal root colonization also decreased in response to repeated clipping. Maximum shoot and root biomass of mycorrbizal plants was produced at 12 and 18 weeks, respectiveIy. Fungicide-treated plants did not grow appro ciably after tbe fit clipping. Thus, mycorrbizae improved clipping tolerance, but with repeated intensive clipping, significant changes in root/shoot ratio occurred and eventually mycorrbizal root colonization and growth benefit were lost.