Plant Nutrient Uptake, 10-08-08

8/13/2019 Plant Nutrient Uptake, 10-08-08

1/19

Month Day Topic C,M&M

Sept. 25 Decomposition 7

30 Soil organic matter 7

Oct. 2 Exam 1-7

7 Nutrient cycles 8

9 Nutrient uptake and

use

8

14 Nitrogen inputs 9

16 Nitrogen dynamics 9

21 Nitrogen loss 9

23 Phosphorus 9


2/19

1. Movement

to the root

2. Uptake

4. Use

3. Loss

Plant nutrient uptake and use


3/19


4/19

1. Nutrient movement to the root: diffusion

and mass flow

Root interceptionis not important

Mass flowis most important for Ca, Mg,

S, micronutrients

Diffusionis most important for N (NO3-),

P, K


5/19

2. Nutrient uptake

Up a concentration gradient

Active transport moves ions across root

cell membranes

Ion specific carriers

Large component of root respiration


6/19

2. Nutrient uptake

After disturbance, controlled by root

length and root activity

Controlled by supply rateat steady

state

Enhanced by mycorrhizae


7/19


8/19

2. Nutrient uptake: Mycorrhizae

Diffusion through mycorrhizae more rapid

than through soil water

80% angiosperms, all gymnosperms

C exchanged for nutrients (4-20% GPP)

Extend root surface into bulk soil

Increase surface area

Ectos AM ericoid orchid


9/19

2. Nutrient uptake

Form

NH4+, NO3

- , Amino acids

PO42-


10/19


11/19

2. Nutrient uptake

But at an ecosystem scale, nutrient

supply is the ultimate constraint on

nutrient uptake

Plant demand for nutrients increases

allocationto nutrient uptake

Increase specific root length Increase density of ion carriers

C investment in mycorrzhiae


12/19

1. Movement

to the root

2. Uptake

4. Use

3. Loss



13/19

3. Nutrient Loss

Plants resorb0-90% of N&P at leaf

senescence (roots? wood?)

Litterfall> leaching > herbivory > exudates

Resorptionis not clearly linked to plant

nutrient status (but is to water status)

Resorptionis sometimes linked to

growthform


14/19

4. Plant nutrient use (THINK: difference between uptakeand loss)

Plant nutrient use efficiency:

Biomass produced per unit nutrient

Nutrient supply effects growth more than iteffects nutrient concentration

Mean residence time of nutrient

Plant NUE =

N productivity x N Turnover Time

TnA*


15/19


16/19

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

4. Plant nutrient use


17/19

5. Ecosystem NUE

Greatest where production is nutrientlimited

Plants maximize Ecosystem NUEin

poor soils by reducing nutrient loss

through longer-lived tissues, not through

increased resorption

Ratio of biomass:N lost in litterfall

(Vitousek 1982)


18/19

Vitousek 1982


19/19

1. Movement

to the root

2. Uptake

4. Use

3. Loss


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Plant Nutrient Uptake, 10-08-08