Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Natural Resources

Department name when degree awarded

Range Ecology


Martyn M. Caldwell


In this dissertation I first examine the ability of individual plants in the field to garner localized soil nutrients. I then measure actual soil variability around perennial plants and use various statistics to quantify the scale and degree of that variability.

Soil patches on opposite sides of Pseudoroegneria spicata tussocks were treated with distilled water or a nutrient solution containing N, P, or K in three field experiments. When P was augmented in the enriched soil patches, rates of P uptake increased significantly for roots from enriched patches compared with roots in control patches. Rates of ammonium and potassium uptake were apparently unchanged. When N was augmented in the enriched patches, rates of ammonium and potassium uptake increased significantly. When K was augmented in the enriched patches, no changes were seen for any of the nutrients.

Plant shading was found to limit the ability of Agropyron desertorum tussocks to increase rates of nutrient uptake in enriched soil microsites. Roots of unshaded plants selectively increased phosphate uptake capacity in enriched patches by up to 73%, but shading limited this response. Enrichment of the soil patches resulted in significantly greater phosphate concentrations in roots of both shaded and unshaded plants.

Nutrient heterogeneity in the soil at a native sagebrush-steppe site was quite high, with ammonium and nitrate varying by over two orders of magnitude and phosphate and potassium close to one order of magnitude within a 10x12- m area. Within 0.5x0.5-m subplots around individual plants, ammonium and nitrate varied by an average factor of 11 and 12, respectively, with less average variation for phosphate and potassium. Geostatistical semivariograms showed that soil ammonium, nitrate, phosphate, potassium, pH, and organic matter all showed detectable autocorrelation only at scales of less than 1.0 to 1.5 m. Indices of microbial activity showed no detectable autocorrelation even at the smallest measurement scale of 12.5 cm. From the degree and scale of heterogeneity encountered, I conclude that root plasticity and active foraging in a heterogeneous soil environment are likely to be important to the nutrient balance of many plants.