Transcript Nutrient Cycles 1. 2. 3. 4. Nutrient requirements Biogeochemical cycles Rates of decomposition Plant adaptations in low nutrient conditions.

Nutrient Cycles
1.
2.
3.
4.
Nutrient requirements
Biogeochemical cycles
Rates of decomposition
Plant adaptations in low nutrient
conditions
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Nutrient Requirements for Plant Growth
• Taken up in gaseous form, Oxygen (O2), Carbon
CO2, and from roots - Water (H2O).
– Derived from water and carbon dioxide
• Rest are taken up from soil solutions
– Macro-nutrients –Nitrogen (N), Phosphorous
(P), Potassium (K),
– Calcium (Ca), Magnesium (Mg), Sulfur (S)
– Micro-nutrients – Boron (B), Copper (Cu), Iron
(Fe), Manganese (Mn), Molybdenum (Mo),
Zinc (Zn)
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Nutrient Cycles
1.
2.
3.
4.
Nutrient requirements
Biogeochemical cycles
Rates of decomposition
Plant adaptations in low nutrient
conditions
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Biogeochemical Cycling
The cycling of nutrients through
ecosystems via food chains and food
webs, including the exchange of nutrients
between the biosphere and the
hydrosphere, atmosphere and geosphere
(e.g., soils and sediments)
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•Ecosystems produce and process energy
primarily through the production and exchange
of carbohydrates which depends on the carbon
cycle.
•Once energy is used, it is lost to the ecosystem
through generation of heat
•Carbon is passed through the food chain
through herbivory, predation, and
decomposition, it is eventually lost to the
atmosphere through decomposition in the form
of CO2 and CH4 . It is then re-introduced into
the ecosystem via photosynthesis.
•However, the amount of carbon present in a
system is not only related to the amount of
primary production, as well herbivory and
predation (e.g., secondary production), it is also
driven by the rates of decomposition by microorganisms
•Atmospheric carbon is rarely limiting to plant
growth
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•When we look at other nutrients, a somewhat different picture emerges than with the energy
cycle – e.g., phosphorous in a food chain within a small pond.
•Algae remove dissolved phosphorous from the water
•The phosphorous is then passed through different trophic levels through herbivory and
predation.
•At each level there is some mortality, and then the phosphorous is passed to decomposers
•These organisms release phosphorous into the water where it is again taken up by primary
producers and the whole cycle starts up again
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Key Elements of Biogeochemical Cycles
a.
Where do the nutrients that ecosystems use come from?
b.
What happens to the nutrients within the ecosystem itself?
c.
What happens to the nutrients once they leave the ecosystem?
d.
Once nutrients are cycled through an ecosystem, how do they get back?
e.
What are the rates of exchange of nutrients between the different pools?
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Nutrient Pools and Nutrient Flux
• Nutrient pool – a specific component or
compartment where a nutrient resides
– Can be a single organism, a population, a
community, a trophic level, and an abiotic
feature (e.g., lake, soil, atmosphere, etc.)
• Nutrient flux – the rate of exchange (e.g.,
unit of material per unit time) of
nutrients between pools
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•Example of changes in the amounts of tracer phosphorous being exchanged within an
aquatic food web
•The values themselves represent changes in the pool levels, where each one of the
lines represents a different pool
•Understanding the feeding relationship allows us to build a nutrient cycle model for
this ecosystem
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Model of phosphorous cycle for an aquatic ecosystem – flux rates per day shown.
1. This system is not closed – inputs, probably from run-off from land.
2. Exports include  herbivores moving outside of system and dead plant/animal material
moving out of system, probably through sedimentation.
3. Rate of uptake by plants is directly proportional to net primary production.
4. Exchange of nutrients by higher trophic levels is controlled by processes regulating
secondary production.
5. Rates of inputs and outputs of nutrients from an ecosystem are driven by both biotic10and
abiotic factors.
Types of Biogeochemical Cycles
Three major categories of biogeochemical
cycles based on slowest-changing
pool(=reservoir):
1. Gaseous cycles of C, O, H20
Global scale
2. Gaseous cycle of N, (S)
3. Sedimentary cycles of the remaining nutrients
Local scale
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Sedimentary Cycles
Gaseous Cycles
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Major Components of Nitrogen Cycle
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Biological Nitrogen Fixers
• Cyanobacteria – blue-green algae
• Free living soil bacteria
• Mycorrhizae
– Symbiotic bacteria living in root
nodules
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Root nodules on ? Cassia fasciculata
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NO from lightning
Lightning + N2 + O2  NO + O2  Nitrate (NO3)
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Phosphorous Cycle
Phosphate – PO4-3
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Potassium
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Sources of Nutrients
Atmosphere
Parent
Material
Run-off,
Ground water
Floods
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Nutrient Cycles
1.
2.
3.
4.
Nutrient requirements
Biogeochemical cycles
Rates of decomposition
Plant adaptations in low nutrient
conditions
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Simple Model of Soil Decomposition/
microbial respiration
H2O, O2
Litter
Energy
Organic Soil
Nutrients
CO2 or CH4
Microbial
Population
Dissolved
Nutrients
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Factors Controlling Microbial
Respiration
1. Availability of oxygen
CO2 versus CH4 production
2. Temperature
3. Moisture
4. Quality of material comprising dead
organic matter
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1
0.9
0.8
Respiration
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Soil Moisture
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2
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Simple Model of Simple Model of Soil
Decomposition/ microbial respiration
H2O, O2
Litter
Energy
Organic Soil
Nutrients
CO2 or CH4
Microbial
Population
Dissolved
Nutrients
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k is the fraction of
a material that decomposes
in a given year
Decomposition as a Function of Lignin Content
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Residence Time
• Residence time is the length of time it
takes for biomass or a nutrient to be
completely decomposed or recycled from
the forest floor
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Residence times
Coniferous forests have longer residence times than deciduous
 C/N control
Boreal forests have longer residence times than temperate forests
 temperature control
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Nutrient Cycles
1.
2.
3.
4.
Nutrient requirements
Biogeochemical cycles
Rates of decomposition
Plant adaptations in low nutrient
conditions
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Tree Nutrient Content
Temperate
Conifers
Temperate
Deciduous
Eucalyptus
%N
%P
%K
0.147
0.043
0.100
0.289
0.025
0.178
0.194
0.008
0.127
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Translocation of Nutrients
• Prior to shedding leaves in the fall,
translocation of nutrients often takes
place in trees
• This allows tree to retain essential
nutrients that are hard to come by
• Spruce trees remove more nutrients than
other coniferous trees
• An adaptation to poor nutrient sites
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Question – do plants growing on sites
with low soil nutrients have low
nutrient contents as well?
The answer is no –
• Plants on sites with low nutrients tend to
have higher nutrient contents
• They have a higher nutrient use efficiency
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Nutrient Use Efficiency (NUE)
• Some plants are more efficient at using
nutrients because it gives them selective
advantages in low nutrient conditions
NUE = A / L
A – the nutrient productivity (dry matter
production per unit nutrient in the plant)
L – nutrient requirements per unit of plant
biomass
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A common pattern found in ecosystem productivity is
saturation curve.
Productivity increases linearly with N availability, up to a
certain point, when other resources become limiting (e.g.,
light, water, temperature, other nutrients)
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Three types of relationships with respect to limitations of
nutrients:
A. Production is independent of resource availability
B. Production is a linear function of resource availability
C. At some point, another resource becomes limiting
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Factors Influencing
Nutrient Availability
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Presence of nitrogen fixers
Microbial activity
Fire
Precipitation patterns
Soil drainage
Soil temperature, moisture
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H2O - Precipitation
CO2
Fire
GHG
Photosynthesis
Internal
translocation
Aeolian,
Atmospheric
Deposition
N 2 , O2
Litterfall
nutrients
N fixers
Organic soil
Dissolved
nutrients
Through-fall
nutrients
Upper mineral soil
Lower mineral soil
CH4, CO2
Nutrients
Energy,
Nutrients
Microbes
Leaching, run off
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Boreal forest has the largest available nutrient pool in soil,
but lowest rates of production, where as tropical forest has
lowest soil pool, and highest production.
Forest Type
Living
Biomass
Pool
Primary
Production
Rates
Soil
Carbon/
Nutrient
Pool
Decomposition
Rates
Tropical
Highest
Highest
Lowest
Highest
Temperate
Middle
Middle
Middle
Middle
Boreal
Lowest
Lowest
Highest
Lowest
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Role of Disturbances in Nutrient Cycling
• Type of disturbance important
– Fire versus logging versus large-scale mortality
• Disturbances directly alter biotic and abiotic
controls on nutrient cycling
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Rates of primary production
Controls on evapotranspiration
Influences on surface runoff
Soil temperature/moisture  decomposition rates
• Linkages between terrestrial/aquatic systems
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Hubbard Brook watershed, upstate New Hampshire.
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Nutrient Cycles
1.
2.
3.
4.
Nutrient requirements
Biogeochemical cycles
Rates of decomposition
Plant adaptations in low nutrient
conditions
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Upland White Spruce Succession
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Nutrient Cycling in Upland White Spruce
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