NUTRIENT-UPTAKE FROM ENRICHED SOIL MICROSITES BY 3 GREAT-BASIN PERENNIALS

Relative nutrient uptake efficiency was measured using a dual-radiotra cer (P-32 and P-33) technique for Agropyron desertorum, Artemisia trid entata, and Pseudoroegneria spicata, species from the arid shrub-stepp e of the Intermountain Region in the western U.S. These species differ ed in the timing and magnitude of their response to experimentally enr iched soil microsites. The most rapid and significant increase in the uptake of phosphorus tracer from enriched microsites was exhibited by Agropyron, followed by Artemisia, while there was only a trend toward an increase in uptake for Pseudoroegneria. The volume of soil enriched was only 4% of the total pot volume yet Agropyron extracted more phos phorus from the enriched microsite than was removed from the remainder (96%) of the soil volume based on tracer uptake from enriched and une nriched microsites. For Agropyron and Pseudoroegneria, plant uptake of phosphorus from microsites was approximately proportional to the soil microsite enrichment and all three species exhibited increased root l ength density within the microsites in proportion to the concentration of available nutrients. Integrated physiological and morphological re sponse of the plants to nutrient enrichment increased phosphorus uptak e, normalized to the amount of phosphorus available in the soil micros ites, by 19.7 to 97.5 x compared to uptake from a similar volume of un enriched soil. Preferential allocation of recently assimilated carbon to roots within enriched soil microsites was also demonstrated. The mo st important differences detected among species were associated with t he temporal flexibility they exhibited in response to enrichment of so il microsites. Differences in flexibility ana response among these spe cies have been reported for other aspects of nutrient uptake, suggesti ve of species-specific differences contributing to demonstrated differ ences in productivity, persistence, and competitive ability.