The belowground microbial community and mycorrhizal fungi in particular may assist potential bioenergy crop production from switchgrass. An earlier growth chamber experiment conducted at the Northern Great Plains Research Laboratory USDA-ARS in Mandan, North Dakota suggested that above- and belowground biomass, tiller numbers and % C in the aboveground biomass were greater for an introduced glomalin source than for a local glomalin source and a mixture of the local and introduced sources.  Although use of the introduced glomalin source resulted in greater biomass production, we hypothesized that the local glomalin source would provide advantages to the switchgrass plants under drought and defoliation stress.  We tested this hypothesis on switchgrass plants using a 3x3x3 factorial arrangement of treatments with 3 different mycorrhizal fungi sources, 3 levels of water stress and 3 levels of defoliation stress in a greenhouse.   Mycorrhizal fungi sources were introduced, local and a mix of local and introduced. Water stress levels were at field capacity, 70% of field capacity and 60% of field capacity.  The study was conducted for 11 weeks. Defoliation levels were undefoliated, clipped to 15 cm every 10 days and clipped to 15 cm every 20 days.  Cumulative above ground biomass at the end of the study was affected by water stress but not mycorrhizal fungi source or defoliation level. Biomass at the mid-point of the study was affected by water stress but not defoliation level for the local and mixed mycorrhizal fungi sources but there was a water stress x defoliation stress interaction for the introduced mycorrhizal fungi source.  Based on the cumulative biomass data, we determined that mycorrhizal source did not affect the above-ground biomass response of switchgrass to water or defoliation stress.  This experiment will be repeated in the greenhouse and below-ground data and C and N responses will also be measured.