| Summary: | From January 1997 through October 1998, research was conducted at Canyonlands National Park to investigate soil traits responsible for distinct spatial patterns of cheatgrass (Bromus tectorum) occurrence. Field experiments were conducted at sites representing a broad range of soil conditions and cheatgrass abundances. Standard physicochemical soil measures in combination with innovative ion-exchange resin capsules and bags were used to describe spatial and seasonal soil variations. Cheatgrass performance varied along a complex, multivariate soil gradient, with the strongest cheatgrass-soil relationship occurring during winter. Biogeochemical principles, soil measures, growth rates, and leaf-tissue analyses support the hypothesis that this complex soil gradient represents a gradient in P dynamics for cheatgrass. A seasonal increase in the solubility of carbonate and calcium-phosphate (Ca- P) compounds should theoretically occur in winter, when cold-moist soil conditions favor the reaction of CO2 and soil H2O to generate carbonic acid, H2CO3. The magnitude of this seasonal acidification phenomenon should vary spatially in relation to pH buffer capacity (acid-neutralizing potential)an important component of soil variation that affects Ca-P dynamics. Insights concerning the significance of pH buffer capacity for P dynamics and cheatgrass nutrition have several implications for research and management.
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