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Root Uptake Kinetics: testing a field method

Root Uptake Kinetics: testing a field method. Jenny Schafer Methods in Ecosystem Ecology April 2004. Question. Do plants with different δ15N signatures differ in their root uptake potentials for different forms of nitrogen (N)? Do species differ in their affinity for different forms of N?.

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Root Uptake Kinetics: testing a field method

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  1. Root Uptake Kinetics:testing a field method Jenny Schafer Methods in Ecosystem Ecology April 2004

  2. Question • Do plants with different δ15N signatures differ in their root uptake potentials for different forms of nitrogen (N)? • Do species differ in their affinity for different forms of N?

  3. Hypotheses • Plants with a depleted (negative) δ15N signature will have greater root uptake potential for nitrate (NO3-). • Plants with an enriched (positive) δ15N signature will have greater root uptake potential for ammonium (NH4+). • Plant species will differ in their affinity for different forms of N.

  4. Methods • Fill vials with known concentrations of NH4+ and NO3-, and distilled water. • Keep some vials in the lab as blanks to check known concentrations. • In the field, put a root in each vial for 30 minutes, and cover the top with parafilm. • We used three different species: Andropogon, Hypericum, and Tradescantia. • Save the roots in labeled bags.

  5. Methods • Dry and weigh roots. • Weigh vials to check for water loss. • Filter the samples to remove dirt. • Keep samples frozen until they can be run on the auto-analyzer (thanks Jennie).

  6. Calculations • Correct all concentrations for the concentration of N in distilled water. • Find the difference in concentration between the blanks and the root samples. • Divide by the mass of the root. • Divide by time. Uptake is a rate. • Generate uptake curves.

  7. Ideal Uptake Curve

  8. Michaelis-Menten Equation Uptake = Vmax * Co Km + Co Vmax = maximum uptake; function of enzyme carriers. Km = MM constant = C at ½ Vmax; function of rates of association. Co = concentration of nutrient outside root surface. Can compare Vmax and Km for different forms of N for the same species or for the same form of N for different species.

  9. Michaelis-Menten Equation Vmax Km

  10. Results • Unfortunately, the uptake curves generated from this experiment were not ideal. • Unable to calculate Vmax and Km.

  11. Andropogon

  12. Hypericum

  13. Tradescantia

  14. Plant Nitrogen Content All species have greater uptake (or less spewing) of NH4+

  15. Possible Explanations • Plant stress – if root dies there is a net efflux of ions. • Plants not active in uptake in the afternoon. • No concentration gradient – diffusion can occur at high concentrations. • Unmeasured water uptake.

  16. Possible Explanations • Needed energy – sugar. C. Cardelus

  17. Conclusions • Test this method before investing a lot of time and effort. • Use excised root uptake methods.

  18. Plant Nitrogen Content

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