Effects of Different Geographic Isolates ofGlomuson the Water Relations ofAgropyron Smithii

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Abstract
The influence of vesicular-arbuscular mycorrhizae on the water relations of the rangeland grass Agropyron smithii was compared for two different geographic isolates of both Glomus macrocarpum var. macrocarpum and G. microcarpum. Spores of these fungi were collected from two sites in Wyoming that differed in total annual precipitation and were used to inoculate greenhouse-grown plants. Leaf resistances to water vapor loss (Rwv) were about 1 1% lower in all mycorrhizal vs. nonmycorrhizal plants at high soil and plant water potentials (>-0.2 MPa) and up to 47% lower at soil and plant water potentials near -6 MPa. Plants infected with G. microcarpum had Rwv values that were up to 26% lower (1520 vs. 1120 m s-1) than G. macrocarpum-infected plants at the lowest xylem pressure potentials. However, changes in xylem pressure potentials over a soil water potential range from 0 to -6 MPa were not statistically different between plants infected with the two fungal congeners. Plants infected with G. microcarpum from the dry Wyoming site had statistically different responses to drying soil than did plants infected with G. microcarpum collected from the more mesic site with an approximate 9% difference in Rwv (1120 m s-1 vs. 1220 m s-1) at a xylem pressure potential near -6 MPa. As was the case for the fungal congeners, xylem pressure potentials of the host A. smithii did not differ between the two G. microcarpum isolates over the range of soil drying.