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Pea ( Pisum sativum cv. Oregon Sugar) Responses to Fertilizer Nitrate Supply

Pea ( Pisum sativum cv. Oregon Sugar) Responses to Fertilizer Nitrate Supply. JulieAnn Rader 2007. Nitrogen Sources. Seed nitrogen. Nitrogen Sources. Seed nitrogen Nitrate-N or ammonium-N assimilation from soil or fertilizer . Nitrogen Sources. Seed nitrogen

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Pea ( Pisum sativum cv. Oregon Sugar) Responses to Fertilizer Nitrate Supply

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  1. Pea (Pisum sativum cv. Oregon Sugar) Responses to Fertilizer Nitrate Supply JulieAnn Rader 2007

  2. Nitrogen Sources • Seed nitrogen

  3. Nitrogen Sources • Seed nitrogen • Nitrate-N or ammonium-N assimilation from soil or fertilizer

  4. Nitrogen Sources • Seed nitrogen • Nitrate-N or ammonium-N assimilation from soil or fertilizer • Biological nitrogen fixation

  5. Nitrogen Fixation • Atmospheric nitrogen is fixed to ammonia by nitrogenase enzymes N2 + 8 H+ + 8 e- 2 NH3 + H2 nitrogenase

  6. Nitrogen Fixation • Atmospheric nitrogen is fixed to ammonia by nitrogenase enzymes N2 + 8 H+ + 8 e- 2 NH3 + H2 nitrogenase

  7. Nodulated roots of a pea legume

  8. Fixation Process

  9. Fixation Process

  10. Fixation Process

  11. Photosynthetic Carbon Cost • Carbon energy required to obtain nitrogen from any external nitrogen source

  12. Previous Studies • Pate (1971): Nitrogen fixation decreases when increased nitrate is available • Viosin et al. (2003): More photosynthetic carbon was allocated to nodules of nitrogen fixing plants as opposed to roots of plants assimilating nitrate-N • Mahon (2001): Plant photosynthesis rates were higher in plants fixing nitrogen than assimilating nitrate-N

  13. Goals • To determine the effects of fertilizer nitrate-N concentration on nitrogen fixation by pea plants (Pisum sativum cv. Oregon Sugar) • To determine if the carbon energy requirement for nitrogen fixation is different from fertilizer nitrate-N assimilation

  14. Shaded and non-shaded pea plants

  15. Hypotheses • Based on Pate: Nitrogen fixation would decrease as fertilizer nitrate-N concentrations increased 2. Based on Voisin et al. and Mahon: Plants fixing nitrogen would have a greater carbon energy requirement than plants assimilating nitrate-N from fertilizer

  16. Methods: Nitrate Fertilizers • Five fertilizers with the following nitrate-N concentrations: 0 (control) µg/mL 10 µg/mL 30 µg/mL 100 µg/mL 500 µg/mL

  17. Methods: Isotope Labeling • Fertilizer nitrate-N was labeled with 15N • Assimilated nitrogen quantified by mass spectroscopy

  18. Methods: Mass Spectroscopy ionization

  19. Methods: Mass Spectroscopy ionization magnetic field acceleration

  20. Methods: Mass Spectroscopy ionization magnetic field acceleration 14N 15N

  21. Methods: Mass Spectroscopy ionization magnetic field acceleration 14N 15N detection

  22. Methods: Photosynthesis Chamber

  23. Methods: Net Photosynthesis

  24. Methods: Net Photosynthesis

  25. Methods: Net Photosynthesis LI-COR CO2 analyzer

  26. LI-COR CO2 analyzer

  27. Results (µg/mL)

  28. Results (µg/mL)

  29. Results (µg/mL)

  30. Results (µg/mL)

  31. Results (µg/mL)

  32. Results (µg/mL)

  33. Results (µg/mL) µ

  34. Results (µg/mL)

  35. Conclusions • Hypothesis supported: nitrogen fixation decreased as fertilizer nitrate-N concentrations increased

  36. Conclusions • Hypothesis supported: nitrogen fixation decreased as fertilizer nitrate-N concentrations increased • Nitrogen fixation began to decline only after concentrations exceeded 30 µg/mL nitrate-N

  37. Conclusions • Hypothesis supported: nitrogen fixation decreased as fertilizer nitrate-N concentrations increased • Nitrogen fixation began to decline only after concentrations exceeded 30 µg/mL nitrate-N • Nitrogen fixed by shaded plants was lower than plants grown in light

  38. Conclusions • Hypothesis supported: nitrogen fixation decreased as fertilizer nitrate-N concentrations increased • Nitrogen fixation began to decline only after concentrations exceeded 30 µg/mL nitrate-N • Nitrogen fixed by shaded plants was lower than plants grown in light • Nitrogen fixation increased from five to seven weeks in all plants

  39. Limitations • No relationship between net photosynthesis and nitrate-N concentration was found

  40. Limitations • No relationship between net photosynthesis and nitrate-N concentration was found • No success in determining carbon energy requirements for nitrogen fixation vs. fertilizer nitrate-N assimilation

  41. Future Work • Pinpoint where nitrogen fixation begins to decline by applying fertilizer nitrate-N concentrations between 30 and 100 µg/mL to pea plants • Measure net photosynthesis rates and repeat study

  42. Acknowledgements • Dr. Michael Russelle • United States Department of Agriculture • University of Minnesota • Ms. Fruen • Team Research

  43. Pea (Pisum sativum cv. Oregon Sugar) Responses to Fertilizer Nitrate Supply JulieAnn Rader 2007

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