Chapter 8 Terrestrial Plant Nutrient Use

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Chapter 8Terrestrial Plant Nutrient Use
Monday, March 9
Essay question 6 assigned.

• Principles of
• Terrestrial Ecosytem Ecology
• Chapin, Matson and Mooney

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Chapter 8Terrestrial Plant Nutrient Use
selections from

• Principles of
• Terrestrial Ecosytem Ecology
• Chapin, Matson and Mooney

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Plants spend gt50 of GPP obtaining water and
nutrients. Plants should always allocate GPP to
obtainingmost limiting resource.
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Nutrient supply is a critical control over NPP
But natural systems dont get fertilizer
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Most nutrients absorbed by plants are recycled
from detritus
Table 8.1, text
N and P 90 recycled!
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All boxes except soil solution are solids and
DO NOT directly provide nutrients to plants
Consumers
Vegetation
Soil organic matter
Litter
Decomposers
Soil solution
1 2 Minerals
Exchangeable
Sorbed
Parent material
Parent material
Leaching
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• Nutrient uptake
• Root mining.
• a. Mass flow from
• soil solution

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Recall the amount of water needed to make a gram
of plants C3 600 cc H20 C4 300 cc H20 CAM 80
cc H20 This water also carries the essential
elements.
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How much production should we expect from 50 cm
of rain per year? Assume C3 It takes 500 g H20
to make a net gain of one gram of plant
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One cm rainfall event on a square Meter produces
10,000 g H20 We get 50 over the year.
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Does the soil solution provide enough
nutrients? Inorganic N in water is 0.2 ppm
N For our prairie example 500,000 g H20
.0000002 of N 0.1 g of N Plants need 4-6 g of
N per year. Not enough!
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The Rhizosphere portion of soil directly
affected by root and root activity.
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Sweet corn (Weaver and Bruner 1927)
over 180 cubic feet of soil are occupied by
the roots of a single plant.
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Roots grow into areas of high nutrient
availability. (most root production near
surface)
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Root elongation is main way plants can increase
nutrient uptake

• Increased rootshoot ratio
• Increased investment in roots
• Root proliferation in nutrient hot spots
• Root growth occurs where it does the most good
• Longer root hairs

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Nutrient uptake 1. Root mining. a) Mass flow
b) diffusion, c) growth/contact,
phosphatase enzyme use. (release phosphotase
enzyme to mine soil for phosphate (HPO4) Has
same problem microbes have with exoenzymes.
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Nutrient Uptake, cont. 2. Hire help !
Mycorrhizal fungi 15 m fungi per cm of
root! up to 20 of GPP to fungi
(rare) certain mycorrhizalspecies have a
protease enzymeprovide amino
acids to plant! may connect different
plant species together.
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The evolution of superorganisms???
(arrows represent flow of nutrients)
plant
litter
plant
Heterotrophic fungi
Mycorrhizal fungi
A closed, external nutrient cycle
Mutualism (but net gain could be less than that
provided other plantaffecting competition
outcome???)
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Nutrient Uptake, cont. 3. Root exudates to use
free living microbes to mineralize
something. 10-30 of GPP exudes
into rhizosphere.! If only composed of
CHO compounds, what is microbial response?
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Nutrient Uptake, cont. Secretion of CHO outside
of roots can be a plant benefit only if
mineralization occurs. (more nutrients made
available to plant) Plants rely on soil
predators of bacteria to provide the goodies!?
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RECALL The release of inorganic nutrients
during decomposition is MINERALIZATION. When
microbes and invertebrates function as
decomposers, if they absorb the nutrients during
the process, the term is called
IMMOBILIZATION. Its fairly common to measure
decomposition (using litterbags) and watch mass
disappear (decomposition) but see NO loss of
nutrients.
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Life in a litterbag Nutrients
Bulk precip
Microflora
Litter
(microbes adhere to litter surface Cannot
separate nutrient content of microbes from
litter.)
Microbivores and Detritivores
Fragmentation and leaching
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Amount of nutrient in decaying substrate
immobilization mineralization
100
Amount Of Nitrogen remaining
time
Strange but true absolute amount of nitrogen
will Increase during the first stages of
decomposition
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Amount of nutrient in decaying substrate
immobilization mineralization
Where does this N come from?
100
Amount remaining
time
Strange but true absolute amount of nitrogen
will Increase during the first stages of
decomposition
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photosynthate
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Rhizosphere is major zone of decomposition in
mineral soil High inputs of labile C prime
decomposition Microbes break down SOM for
nitrogen
Figure 7.11
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• Root uptake tricks
• mass flow
• diffusion
• direct contact (?)
• 2) Mycorrhizae pay-off
• pay fungus to do the job
• 3) Microbial mayhem?
• dump photosynthate (CHO)
• and hope to get nutrients?

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4
Hydraulic Lift (see pg 84, text)
The dilemma plant has no way of
getting nutrients from dry soil
nutrients
water
(no nutrients)
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Hydraulic Lift
moon
Solution at night water leaks out of roots
in upper dry zone.
Text book misses an opportunity hereits not
just water oozing into the soil!
nutrients
water
(no nutrients)
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Hydraulic Lift
During day water is withdrawn. Net
result provides nutrients. (this result could be
a logical consequence of root herbivory?)
Plants Capable of small organic molecule
uptake, too!
nutrients
water
(no nutrients)
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• Summary of root uptake mechanisms
• Root growth/activity
• mass flow, diffusion, contact, hydraulic
  lift
• 2) Hire mycorrhizae to use as roots
• (cold regions have fewest mycorrhizae)
• 3) Benefit from root exudates of organic
• carbon. (requires mineralization of
  microbes)

Plants allocate gt50 GPP to belowground
activities
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All of these uptake mechanisms should deplete
soil nutrients from all non-organic
sources? How are these replaced from losses due
to leaching, physical export, surface erosion,
etc?
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All boxes except soil solution are solids and
DO NOT directly provide nutrients to plants
Soil organic matter
Consumers
Vegetation
Litter
Decomposers
Soil solution
1 2 Minerals
Exchangeable
H
H
Sorbed
Parent material
Parent material
Leaching
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