Sagebrush (Artemisia tridentataNutt.) roots maintain nutrient uptake capacity under water stress

Phosphorus and nitrogen uptake capacities wereassessed during 36-58 d drying cycles to determinewhether the ability of sagebrush {Artemisia tridentataNutt.) to absorb these nutrients changed as the rootswere subjected to increasing levels of water stress.Water was withheld from mature plants in large (6 I)containers and the uptake capacity of excised roots insolution was determined as soil water potentialsdecreased from —0.03 MPa to —5.0 MPa.Phosphorus uptake rates of excised roots at givensubstrate concentrations increased as preharvest soilwater potentials decreased to —5.0 MPa. ^ and K m also increased as soil water potentials declined.Declining soil water potentials depressed nitrogenuptake at set substrate concentrations, but uptakecapacity, calculated as the sum V mMX for bothNH 4+ +NO 3 ~, did not change significantly with drying.The sum V mMX correlated with root nitrogenconcentration.Root uptake capacity for nitrogen and phosphoruswas extremely stable under severe water stress inthis aridland shrub. Maintenance of uptake capacity,coupled with a previously demonstrated ability toconduct hydraulic lift, may enable A. tridentata betterto maintain nitrogen and phosphorus uptake as soilwater availability declines. These mechanisms maybe important in the ability of A. tridentata to main-tain growth, complete reproduction, and gain anadvantage against competitors late in the seasonwhen the soil layers with higher nutrient availabilityare dry.