Transcript INTRODUCTION - Penn State York Home Page

Nutrient Cycling and Retention
Chapter 19
www.sws.uiuc.edu/ nitro/biggraph.asp
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Focus Areas
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Nutrient Cycles
 Phosphorus
 Nitrogen
 Carbon
Rates of Decomposition
 Terrestrial
 Aquatic
Organisms and Nutrients
Disturbance and Nutrients
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Phosphorus Cycle
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Global phosphorus cycle does not include
substantial atmospheric pool.
 Largest quantities found in mineral
deposits and marine sediments.
 Much of this in forms not directly
available to plants.
 Slowly released in terrestrial and aquatic
ecosystems via weathering of rocks.
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Phosphorus Cycle
http://arnica.csustan.edu/carosella/Biol4050W03/figures/phosphorus_cycle.htm 4
Nitrogen Cycle
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Includes major atmospheric pool - N2.
 Nitrogen fixers can use atmospheric supply
directly (only prokaryotes).
 Energy-demanding process; reduces to N2 to
ammonia (NH3).
 Industrial N2- fixation for fertilizers equals the
biological process annually.
 Denitrifying bacteria release N2 in anaerobic
respiration (they “breath” on nitrate).
 Decomposer and consumers release waste N in
form of urea or ammonia.
 Ammonia is nitrified by bacteria to nitrate.
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Nitrogen Cycle
http://muextension.missouri.edu/xplor/envqual/wq0252.htm
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Carbon Cycle
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Moves between organisms and atmosphere
as a consequence of photosynthesis and
respiration.
 In aquatic ecosystems, CO2 must first
dissolve into water before being used by
primary producers.
 Although some C cycles rapidly, some
remains sequestered in unavailable forms
for long periods of time.
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Carbon Cycle
http://www.ucar.edu/learn/images/carboncy.gif
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Rates of Decomposition
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Rate at which nutrients are made available
to primary producers is determined largely
by rate of mineralization.
 Occurs primarily during decomposition.
 Rate in terrestrial systems is
significantly influenced by temperature,
moisture, and organic chemical
compositions (labile versus refractory).
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Decomposition in Temperate
Woodland Ecosystems
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Gallardo and Merino found differences in
mass loss by the target species reflected
differences in the physical and chemical
characteristics of their leaves.
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Decomposition in Temperate Forest
Ecosystems
Melillo et.al. used litter bags to study
decomposition in temperate forests.
 Found leaves with higher lignin:nitrogen
ratios lost less mass.
 Suggested higher N availability in soil
might have contributed to higher
decomposition rates.
 Higher environmental temperatures
may have also played a role.
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Decomposition in Aquatic Ecosystems
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Gessner and Chauvet found leaves with a
higher lignin content decomposed at a
slower rate.
 Higher lignin inhibits fungi colonization of
leaves.
Suberkropp and Chauvet found leaves
degraded faster in streams with higher
nitrate concentrations.
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Decomposition in Aquatic Ecosystems
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Nutrient Cycling in Streams
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Webster pointed out nutrients in streams are
subject to downstream transport.
 Little nutrient cycling in one place.
 Nutrient Spiraling
 Spiraling Length is the length of a stream
required for a nutrient atom to complete a
cycle.
 Related to rate of nutrient cycling and
velocity of downstream nutrient
movement.
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Nutrient Spiraling in Streams
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Stream Invertebrates and Spiraling Length
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Grimm showed aquatic invertebrates
significantly increase rate of N cycling.
 Suggested rapid recycling of N by
macroinvertebrates may increase primary
production.
 Excreted and recycled 15-70% of
nitrogen pool as ammonia.
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Stream Invertebrates and Spiraling Length
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Animals and Nutrient Cycling in
Terrestrial Ecosystems
MacNaughton found a positive relationship
between grazing intensity and rate of
turnover in plant biomass in Serengeti Plain.
 Without grazing, nutrient cycling occurs
more slowly through decomposition and
feeding of small herbivores.
Huntley and Inouye found pocket gophers
altered N cycle by bringing N-poor subsoil to
the surface.
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Animals and Nutrient Cycling in
Terrestrial Ecosystems
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Disturbance and Nutrient Loss From the
Hubbard Brook Forest
Likens and Bormann
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Disturbance and Nutrient Loss
from Diverse Forest Types
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Vitousek studied effects of disturbance and
environmental conditions on N loss.
 Trenching increased concentrations of
nitrate in soil water up to 1,000 x.
 Nitrate losses are generally greatest at
sites with rapid decomposition.
 Uptake by vegetation is most
important in ecosystems with fertile
soils and warm, moist conditions.
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Flooding and Nutrient Export by Streams
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Meyer and Likens found P exports were
highly episodic and associated with periods
of high flow.
 Annual peak in P input associated with
spring snowmelt.
 Most export was irregular because it
was driven by flooding caused by
intense periodic storms.
Inter-annual variation in balance of inputs
and exports indicate tha low flow years are
storage years.
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Flooding and Nutrient Export by Streams
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Human influences on nutrient cycling
Loss of nutrients via deforestation
• Addition of nutrients
 Fertilizers
 Nitrogen in atmosphere from coal burning
Consequences
 Reduced biodiversity
 Reduction of mycorrhizal fungi
 Eutrophication of lakes
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http://www.epa.gov/maia/html/eutroph.html
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(Peierls et al., 1991)
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