Root Exploitation of Fertile Soil Microsites

Root exploitation of enriched soil microsites was examined for the tussock grasses Agropyron desertorum and Agropyron spicatum and the shrub Artemisia tridentata. Two mechanisms of exploitation of the microsites were examined: root proliferation and changes in nutrient uptake capacity. One day after nutrient solution was applied to small soil patches, the mean relative growth rate of Agropyron desertorum roots in enriched patches was two to four times greater than for roots of the same plants in soil patches treated with distilled water. This rapid and striking root proliferation occurred in response to N-P-K enrichment as well as to P or N enrichment alone. Agropyron spicatum showed no tendency to proliferate roots in enriched soil patches during the 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 other experiments. The ability of Agropyron desertorum partly explain its to proliferate superior ability roots to rapidly may exploit soil nutrients compared to Agropyron spicatum in Great Basin rangelands of North America. Changes in nutrient uptake capacity in enriched soil patches were also studied for each species. rapid changes in uptake capacity of plant roots Large and from the field were observed after creation of nutrient-rich patches in the soil. Phosphate uptake of excised roots from enriched soil patches was roots of control patches as much as 80% greater than for treated with distilled water. These increases in uptake capacity took place within one week of patch treatment for all three species. A follow-up experiment showed increases within three days of patch treatment. These results showing rapid physiological plasticity in roots exploiting nutrient patches have important implications for nutrient belowground competition among plants