The rangeland grass, Bouteloua gracilis was inoculated with its mycorrhizal symbiont, Glomus
fasciculatus, to determine the influence of vesicular-arbuscular mycorrhizae on water status,
stomatal behaviour and photosynthesis as well as gross plant morphology, biomass and
phosphorus content. Mycorrhizal infection increased transpiration rates by over 100 % with 50
to 70 % lower leaf resistances to water vapour diffusion. Leaf xylem pressure was not different
between mycorrhizal and non-mycorrhizal plants indicating that whole-plant resistance to water
transport was reduced by more than 50 %. Photosynthetic rates under saturating light conditions
increased 68 % with infection as a consequence of a 33 % reduction in stomatal resistance and
a 67 % reduction in mesophyll resistance to CO2 uptake. Mycorrhizal infection did not affect
biomass or gross plant morphology after 30 weeks of growth, but increased chlorophyll and
phosphate concentrations by 28 % and 70 % respectively. These physiological changes indicate
that mycorrhizae may substantially alter survival ability of Bouteloua gracilis.