WHEAT RESPONSES TO VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGAL INOCULATION OF SOILS FROM ERODED TOPOSEQUENCE

Low fertility of eroded soils is often attributed to the loss of topso il, an important source of nutrients for microorganisms and plants. Ve sicular-arbuscular mycorrhizal (VAM) fungi are known to improve nutrie nt uptake by plants from infertile soil. The objective of this study w as to determine whether wheat (Triticum aestivum L.) responses to VAM fungal inoculation differ among eroded and noneroded soils from the sa me toposequence. Spring wheat plants were grown under growth chamber c onditions in soils collected from three landscape positions of a typic al toposequence in eastern Washington, with and without VAM fungal ino culation. Noninoculated soils exhibited 13 to 26% VAM root colonizatio n, while inoculation increased VAM colonization up to 49 to 55% by 5 w k after planting. The VAM fungal inoculation of eroded soils increased shoot dry weight and tiller number, advanced the leaf stage, and incr eased root length compared with the noninoculated controls. Shoot conc entrations of P and Zn were increased by VAM inoculation. In contrast, shoot concentrations of Cu and Mn were unchanged, while Fe was decrea sed. While VAM fungal inoculation also increased P, Zn, and Cu concent rations in water-stressed plants, Mn and Fe concentrations decreased. No responses to VAM fungal inoculation were observed in soil from a no neroded toeslope, although VAM colonization was similar to that observ ed in the eroded soils. These results indicate the potential role of V AM fungi for improving dryland wheat productivity on eroded soils.