Plant nutrient uptake and use

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Plant nutrient uptake and use
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• 1. Nutrient movement to the root diffusion and
  mass flow

• Diffusion is most important for N (NO3-), P, K

• Mass flow is most important for Ca, Mg, S,
  micronutrients

• Root interception is not important

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• 2. Nutrient uptake

• Active transport moves ions across root cell
  membranes

Up a concentration gradient
Ion specific carriers
Large component of root respiration
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• 2. Nutrient uptake

• Controlled by supply rate at steady state

• After disturbance, controlled by root length and
  root activity

• Enhanced by mycorrhizae

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• 2. Nutrient uptake Mycorrhizae

• 80 angiosperms, all gymnosperms

• 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
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• 2. Nutrient uptake

• Form
• NH4, NO3- , Amino acids
• PO42-

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• 2. Nutrient uptake

• Plant demand for nutrients increases allocation
  to nutrient uptake
• Increase specific root length
• Increase density of ion carriers
• C investment in mycorrzhiae

• But at an ecosystem scale, nutrient supply is the
  ultimate constraint on nutrient uptake

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Plant nutrient uptake and use
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• 3. Nutrient Loss

• Litterfall gt leaching gt herbivory gt exudates

• Plants resorb 0-90 of NP 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

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• 4. Plant nutrient use (THINK difference between
  uptake and loss)
  
  
  
  
  
  
  
  
  

• Nutrient supply effects growth more than it
  effects nutrient concentration

• Plant nutrient use efficiency
• Biomass produced per unit nutrient

• Mean residence time of nutrient

Plant NUE N productivity x N Turnover Time
Tn
A
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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

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• 5. Ecosystem NUE

• Ratio of biomassN 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

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Vitousek 1982
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Plant nutrient uptake and use