Sagebrush (Artemisia tridentata Nutt.) roots maintain nutrient uptake capacity under water stress
1996
Matzner, S.L. | Richards, J.H.
Phosphorus and nitrogen uptake capacities were assessed during 6-58 d drying cycles to determine whether the ability of sagebrush (Artemisia tridentata Nutt.) to absorb these nutrients changed as the roots were subjected to increasing levels of water stress. Water was withheld from mature plants in large (6 l) containers and the uptake capacity of excised roots in solution was determined as soil water potentials decreased from 0.03 MPa to -5.0 MPa. Phosphorus uptake rates of excised roots at given substrate concentrations increased as preharvest soil water potentials decreased to - 5.0 MPa. Vmax and Km also increased as soil water potentials declined. Declining soil water potentials depressed nitrogen uptake at set substrate concentrations, but uptake capacity, calculated as the sum Vmax for both NH4+ +NO3-, did not change significantly with drying. The sum Vmax correlated with root nitrogen concentration. Root uptake capacity for nitrogen and phosphorus was extremely stable under severe water stress in this aridland shrub. Maintenance of uptake capacity, coupled with a previously demonstrated ability to conduct hydraulic lift, may enable A. tridentata better to maintain nitrogen and phosphorus uptake as soil water availability declines. These mechanisms may be important in the ability of A. tridentata to maintain growth, complete reproduction, and gain an advantage against competitors late in the season when the soil layers with higher nutrient availability are dry.
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