Graduate Thesis Or Dissertation
 

An Investigation of soil, vegetation and mycorrhizal characteristics associated with native grass re-esablishment in crested wheatgrass seedings

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  • Since the 1930's, many fields on the Crooked River National grasslands have been seeded to crested wheatgrass (Agropyron desertorum). While some of these fields remain dominated by crested wheatgrass others had a greater presence of deep rooted native perennial grasses such as bluebunch wheatgrass (Pseudoroegneria spicata). Twenty eight fields previously seeded to crested wheatgrass were sampled to determine vegetation composition, soil nutrient status, and depth to the restrictive layer. Fourteen of the fields had a greater presence of native grasses and fourteen remain dominated by crested wheatgrass. In addition, root samples were collected from 10 of the 28 fields to determine the percent of root length colonized by mycorrhizae for crested wheatgrass and bluebunch wheatgrass. Soil samples from a random sample often fields were used to determine the genera of mycorrhizal fungi present. Vegetation and soil data were analyzed using multivariate methods. Results indicated that the two field types were different with respect to species composition confirming the appropriateness of the site selection criteria. The associated soil environmental variables also differed between field type. The strongest association was that of soil particle size. Fields with a greater presence of native grasses were positively associated with soils having a higher percent of clay and silt. Fields where crested wheatgrass remained dominant were strongly associated with soil having a higher percent sand. Other soil environmental variables that were positively associated with each field type were exchangeable magnesium, percent organic matter for the fields with a greater presence of native grasses and exchangeable potassium and extractable phosphorus with the crested wheatgrass fields. The data for percent of root length colonized by mycorrhizae were analyzed using a one way analysis of variance. The results indicated that there was no difference in percent root length colonized between crested wheatgrass and bluebunch wheatgrass. There were 4 genera of mycorrhizal fungi present on the 10 fields evaluated and none of these genera were exclusive to either field type. The crested wheatgrass fields with a greater presence of native grasses were different from those remaining dominated by crested wheatgrass with respect to vegetation and soils characteristics. Further work needs to be done to establish membership of the mycorrhizal community.
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