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Decreases in Soil Microbial Function and Functional Diversity in Response to Depleted Uranium

Center for Ecological Risk Assessment and Management, Dep. of Fishery and Wildlife Biology, Colorado State Univ., Fort Collins, CO 80523,

Mark W. Paschke

Center for Ecological Risk Assessment and Management, Colorado State Univ., Fort Collins, CO 80523;

Terry McLendon

Dep. of Biological Sciences, Univ. of Texas at El Paso, El Paso, TX 79968,

David Price

U.S. ARMY Construction Engineering Res. Labs., Champaign, IL 61826.

^* Corresponding author.

ABSTRACT

A soil microcosm experiment was used to analyze effects of depleted uranium (DU) on soil function, and the concomitant changes in bacterial functional diversity. Uranium treatment levels were 0, 50, 500, 5000, 10 000, and 25 000 mg DU kg^–1 soil. Three measures of soil function were made. Overall soil biological activity was assessed via measurement of soil respiration. Decomposition was assessed by measurement of mass loss of four different plant litter types: wood sticks, cellulose paper, high-N grass, and low-N grass. Mineral N availability in the microcosms was estimated using ion-exchange resin bags. Functional diversity of the microcosms was analyzed through the use of the Biolog-system of sole-C-utilization patterns. Soil respiration was the most sensitive measure of functional changes, with significant decreases observed starting at the 500 mg kg^–1 treatment. No differences in N availability were observed across the U treatments. Litter decomposition was significantly decreased (P < 0.05) at the 25 000 mg kg^–1 level relative to the control for all litter types except the high-N grass. Wood decomposition was reduced by 84% at the 25 000 mg kg^–1 treatment, cellulose paper by 68%, and low-N grass by 15%. Decreases in the functional diversity of the bacterial community were related to the observed decrease in soil respiration, and to the greater effect on decomposition of the lower-quality litter types.

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Received for publication October 6, 1997.