|Bassirirad, Hormoz - UNIVERSITY OF ILLINOIS|
|Norby, Rich - OAK RIDGE NAT'L LAB|
|Rogers Jr, Hugo|
Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 31, 1999
Publication Date: December 1, 1999
Citation: BassiriRad, H., Prior, S.A., Norby, R.J., and Rogers, H.H. 1999. A field method of determining NH+4 and NO-3 uptake kinetics in intact roots: Effects of CO2 enrichment on trees and crop species. Plant and Soil 217 (1/2):195-204. Interpretive Summary: Models characterizing how plants and ecosystems cycle nitrogen in the field (under conditions such as the well documented rise in atmospheric CO2 level) rely on accurate measurement of root nitrogen uptake. Since old laboratory uptake methods using root cuttings may not be accurate, a new field method was developed to measure nitrogen uptake from intact root systems of crops (soybean and sorghum) and trees (red and sugar maple). Findings showed that crop roots had a higher capacity to take up various forms of nitrogen (nitrate or ammonium) compared to tree roots and that elevated CO2 increased uptake of ammonium for red maple only. Results demonstrated that this new method can be used in the field to measure nitrogen uptake from intact root systems.
Technical Abstract: Models describing plant and ecosystem N cycles require an accurate assessment of root uptake capacity for NH4 and NO3 under field conditions. Traditionally, rates of ion uptake in field-grown plants are determined using excised root segments incubated for a short period in solution containing N either as a radioactive or stable isotope tracer. Although reliable, this method has drawbacks. For example, in addition to radioactive safety issues, purchase and analysis of radioactive and stable isotopes is expensive and can be a limitation. More importantly, since excision interrupts exchange of compounds between root and shoot (e.g., carbohydrate supply to root and N transport to shoot), the assay must be conducted quickly to avoid complications. Here we present a novel field method for simultaneous measurements of NH4 and NO3 uptake kinetics in intact root systems. The application of this method is shown using two tree species; red maple (Acer rubrum) and sugar maple (Acer saccharum) and two crop species soybean (Glycine max) and sorghum (Sorghum bicolor). Plants were grown in open-top chambers (ambient and elevated levels of atmospheric CO2) at two US national CO2 research sites involved in CO2 research. Absolute values of net uptake rates and the kinetic parameters determined by our method were in agreement with literature reports. Roots of crops exhibited a greater uptake capacity for both N forms relative to trees. Elevated CO2 did not affect kinetics of N uptake in species tested except in red maple where it increased root uptake capacity (Vmax) for NH4. The application, reliability, advantages and disadvantages of the method are discussed in detail.