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1. Movement to the root

4. Use. 3. Loss. 2. Uptake. 1. Movement to the root. Plant nutrient uptake and use. 1. Nutrient movement to the root: diffusion and mass flow. Diffusion is most important for N (NO 3 - ), P, K. Mass flow is most important for Ca, Mg, S, micronutrients.

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1. Movement to the root

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  1. 4. Use 3. Loss 2. Uptake 1. Movement to the root Plant nutrient uptake and use

  2. 1. Nutrient movement to the root: diffusion and massflow • Diffusion is most important for N (NO3-), P, K • Mass flow is most important for Ca, Mg, S, micronutrients • Root interception is not important

  3. Active transport moves ions across root cell membranes 2. Nutrient uptake Up a concentration gradient Ion specific carriers Large component of root respiration

  4. Controlled by supply rate at “steady state” 2. Nutrient uptake • After disturbance, controlled by root length and root activity • Enhanced by mycorrhizae

  5. 80% angiosperms, all gymnosperms 2. Nutrient uptake: Mycorrhizae • C exchanged for nutrients (4-20% GPP) • Extend root surface into bulk soil • Increase surface area • Diffusion through mycorrhizae more rapid than through soil water Ectos, AM, ericoid, orchid

  6. Form • NH4+, NO3- , Amino acids • PO42- 2. Nutrient uptake

  7. Plant demand for nutrients increases allocation to nutrient uptake • Increase specific root length • Increase density of ion carriers • C investment in mycorrzhiae 2. Nutrient uptake • But at an ecosystem scale, nutrient supply is the ultimate constraint on nutrient uptake

  8. 4. Use 3. Loss 2. Uptake 1. Movement to the root Plant nutrient uptake and use

  9. Litterfall > leaching > herbivory > exudates 3. Nutrient Loss • Plants resorb 0-90% of N&P at leaf senescence (roots? wood?) • Resorption is not clearly linked to plant nutrient status (but is to water status) • Resorption is sometimes linked to growthform

  10. Nutrient supply effects growth more than it effects nutrient concentration 4. Plant nutrient use (THINK: difference between uptake and loss) • Plant nutrient use efficiency: • Biomass produced per unit nutrient • Mean residence time of nutrient Plant NUE = N productivity x N Turnover Time A* Tn

  11. 4. Plant nutrient use • Infertile sites •  N TT x  N productivity • Fertile sites •  TT x  N productivity • Result:Less difference in NUE across fertility gradients than you would expect given nutrient supply rates

  12. 5. Ecosystem NUE • Ratio of biomass:N lost in litterfall • (Vitousek 1982) • Greatest where production is nutrient limited • Plants maximize Ecosystem NUE in poor soils by reducing nutrient loss through longer-lived tissues, not through increased resorption

  13. Vitousek 1982

  14. 4. Use 3. Loss 2. Uptake 1. Movement to the root Plant nutrient uptake and use

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