NUTRIENT CYCLING AND RETENTION
Chapter 19
Molles: Ecology 2nd Ed.
Chapter Concepts
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Decomposition rate influenced by
temperature, moisture, and chemical
composition of litter and environment
Plants and animals modify distribution and
cycling of nutrients in ecosystems
Disturbance increases ecosystem nutrient
loss
Molles: Ecology 2nd Ed.
Phosphorus Cycle
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Global phosphorus cycle doesn’t include
substantial atmospheric pool
 Largest quantities of P are in mineral
deposits and marine sediments
 Much of this not directly available to
plants
 Slowly released in terrestrial and aquatic
ecosystems – weathering of rocks
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.
Nitrogen Cycle
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Includes major atmospheric pool – N2
 Only nitrogen fixers can use atmospheric
supply directly
 Blue-green algae, soil bacteria, bacteria
of legume roots, some fungi
 = energy-demanding process
 N2 reduced to ammonia (NH3)
Molles: Ecology 2nd Ed.
•
Nitrogen fixers fix nitrogen = anaerobic
(stinks)
Once N fixed – available to organisms
 Upon death of organism, N can be
released by fungi and bacteria during
decomposition
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.
Carbon Cycle
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Moves between organisms and atmosphere
due to photosynthesis and respiration
 In aquatic ecosystems, CO2 dissolves into
water – then used by primary producers
 Although some C cycles rapidly, some
remains stored in unavailable forms for
long time
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.
Decomposition Rates
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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 influenced by
temperature, moisture, and chemical
compositions
Molles: Ecology 2nd Ed.
Decomposition in Temperate Forest Ecosystems
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Melillo et.al. (1982)
Litter bags to study decomposition in
temperate forests:
 Leaves with higher lignin:nitrogen ratios
lost less mass
 = higher N availability in soil might have
contributed to higher decomposition
rates
Molles: Ecology 2nd Ed.
Fig. 19.7
Molles: Ecology 2nd Ed.
Decomposition in Aquatic Ecosystems
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Gessner and Chauvet (1994)
Stream in French Pyrenees
Leaves with more lignin decomposed slower
 Higher lignin inhibits fungi colonization of
leaves
Molles: Ecology 2nd Ed.
Suberkropp and Chauvet
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Tulip tree leaves degraded faster in Alabama
streams with higher nitrate concentrations
Molles: Ecology 2nd Ed.
Nutrient Cycling in Streams
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Webster (1975) – nutrients in streams are
subject to downstream transport
 Little nutrient cycling in one place
 Nutrient Spiraling
Fig 19.13
Molles: Ecology 2nd Ed.
Webster (1975)

Spiraling Length = length of stream
required for a nutrient atom to complete a
cycle
 Related to rate of nutrient cycling and
velocity of downstream nutrient
movement
Fig 19.13
Molles: Ecology 2nd Ed.
Nutrient Cycling in Streams
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Spiraling Length:
S = VT
S = Spiraling Length
V = Average velocity of nutrient atom
T = Average time to complete cycle
 Short lengths = high nutrient retentiveness
 Long lengths = low nutrient retentiveness
Fig 19.13
Molles: Ecology 2nd Ed.
Stream Invertebrates and Spiraling Length
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Grimm (1988):
 Sycamore Creek, AZ
 Collector-gatherer insect larvae
 Mayflies + chironomids
 Aquatic invertebrates increase rate of N
cycling
Molles: Ecology 2nd Ed.
•
How much N do invert’s contribute to
nutrient dynamics of stream?
Rapid recycling of N by macroinvertebrates
increases primary production
 Excreted and recycled 15-70% of
nitrogen pool as ammonia
Molles: Ecology 2nd Ed.
Fig. 19.14
Molles: Ecology 2nd Ed.
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Animals and Nutrient Cycling in
Terrestrial Ecosystems
Huntley and Inouye (1988)
 Pocket gophers alter N cycle by bringing
N-poor subsoil to surface
Molles: Ecology 2nd Ed.
MacNaughton et al. (1988)
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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
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.
Plants and Ecosystem Nutrient Dynamics
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Fynbos is a South African temperate
shrub/woodland known for high plant diversity
and low soil fertility
 Two species of Acacia introduced to
stabilize shifting sand dunes
Molles: Ecology 2nd Ed.
Witkowski (1991)
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Compared nutrient dynamics under canopy
of native shrub and introduced Acacia
 Amount of litter similar, but nutrient
content was significantly different
 Acacia – N fixer
Molles: Ecology 2nd Ed.
Introduced Tree and Hawaiian Ecosystem
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Native flora = 1,200 species
 > 90% endemic
 ~ 4,600 new species introduced
to Hawaii
 Firetree
 Myrica faya
Molles: Ecology 2nd Ed.
Vitousek and Walker (1989)
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Invading N-fixing tree Myrica faya is altering
N dynamics of Hawaiian ecosystems
 Introduced in late 1800’s as ornamental or
medicinal plant – later used for watershed
reclamation
 Nitrogen fixation by Myrica large N input
 Leaves contain high N content
– High decomposition rate
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.
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Disturbance and Nutrient Loss From the
Hubbard Brook Forest
Vitousek et al.
19 forests around N. America
 11 deciduous, 8 coniferous
 Acidic to neutral soils
Effects of disturbance and environmental
conditions on N loss
Molles: Ecology 2nd Ed.
Vitousek studies:
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Square meter plots
 Dig trenches around them, line w/plastic
Trenching increased concentrations of
nitrate in soil water up to 1,000X
 Nitrate losses higher at sites with rapid
decomposition
 Uptake by vegetation most important
in ecosystems with fertile soils and
warm, moist conditions
Molles: Ecology 2nd Ed.
Similar study on disturbance by forest clearcutting:
Fig 19.21
Molles: Ecology 2nd Ed.
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
Molles: Ecology 2nd Ed.
Summary
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•
•
Decomposition rate influenced by
temperature, moisture, and chemical
composition of litter and environment
Plants and animals modify distribution and
cycling of nutrients in ecosystems
Disturbance increases ecosystem nutrient
loss
Molles: Ecology 2nd Ed.
Molles: Ecology 2nd Ed.