Month Day Topic
Sept.
25
Decomposition
30
Soil organic matter
Oct.
2
Exam
7
Nutrient cycles
9
Nutrient uptake and
use
14
Nitrogen inputs
16
Nitrogen dynamics
21
Nitrogen loss
23
Phosphorus
C,M&M
7
7
1-7
8
8
9
9
9
9
Plant nutrient uptake and use
4. Use
3. Loss
2. Uptake
1. Movement
to the root
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
2. Nutrient uptake
• Active transport moves ions across root
cell membranes
Up a concentration gradient
Ion specific carriers
Large component of root respiration
2. Nutrient uptake
• Controlled by supply rate at “steady
state”
• After disturbance, controlled by root
length and root activity
• Enhanced by mycorrhizae
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
2. Nutrient uptake
• Form
• NH4+, NO3- , Amino acids
• PO42-
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
Plant nutrient uptake and use
4. Use
3. Loss
2. Uptake
1. Movement
to the root
3. Nutrient Loss
• Litterfall > leaching > herbivory > exudates
• 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
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
A*
Tn
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
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
Vitousek 1982
Plant nutrient uptake and use
4. Use
3. Loss
2. Uptake
1. Movement
to the root