The timing and degree of root proliferation in fertile-soil microsites for three cold-desert perennials

Summary. Root proliferation in nutrient-rich soil patches is an important mechanism facilitating nutrient capture by plants. Although the phenomenon of root proliferation is well documented, the specific timing of this proliferation has not been investigated. We studied the timing and degree of root proliferation for three perennial species common to the Great Basin region of North America: a shrub, Ar-temisia tridentata, a native tussock grass, Agropyron spica-turn, and an introduced tussock grass, Agropyron deser-torum. One day after we applied nutrient solution to small soil patches, the mean relative growth rate of Agropyron desertorurn roots in these soil patches was two to four times greater than for roots of the same plants in soil patches treated with distilled water. Most of the increased root growth came from thin, laterally branching roots within the patches. This rapid and striking root proliferation by Agropyron desertorurn occurred in response to N-P-K en-richment as well as to P or N enrichment alone. A less com-petitive bunchgrass, Agropyron spicatum, showed no ten-dency to proliferate roots in enriched soil patches during these two-week experiments. The shrub Artemisia tridentata proliferated roots within one day of initial solution injection in the N-enrichment experiment, but root proliferation of this species was more gradual and less consistent in the N-P-K- and P-enrichment experiments, respectively. The ability of Agropyron desertorum to proliferate roots rapidly may partly explain both its general competitive success and its superior ability to exploit soil nutrients compared t