Chap.20 Ecosystem Energetics
Chap.21 Decomposition and nutrient cycling
Chap.22 Biogeochemical cycles
Smith & Smith (2015) Elements of ecology. 9th. Ed. Pearson.
Part Six Ecosystem Ecology
生態體系 生態學
鄭先祐 (Ayo) 教授
生態科學與技術學系
國立臺南大學 環境與生態學院
Chap.22 生物地理化學循環
Biogeochemical Cycles
Smith & Smith (2015) Elements of ecology. 9th. Ed. Pearson.
鄭先祐 (Ayo) 教授
生態科學與技術學系
國立臺南大學 環境與生態學院
Impala (Aepyceros melampus) standing in the shade of acacia trees.
Their urine and droppings make the impala important contributors
to the internal nitrogen cycle of these trees.
3
Chapter 22 Biogeochemical Cycles
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 Many chemical reactions take place in abiotic
components of the ecosystem.
 Atmosphere
 Water
 Soil
 Parent material
 The biogeochemical cycle is the cyclic flow of
nutrients from the nonliving to the living and back
to the nonliving components of the ecosystem.
4
22.1 There Are Two Major Types of
Biogeochemical Cycles
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Two types of biogeochemical cycles
1. In gaseous biogeochemical cycles, the main pools of nutrients
are the atmosphere and the oceans
 Global
 Nitrogen, carbon dioxide, oxygen
2. In sedimentary biogeochemical cycles, the main pool of
nutrients is the soil, rocks, and minerals
 Inorganic sources of minerals are released to living animals
through weathering and erosion
 Phosphorus
 Hybrid of gaseous and sedimentary cycles occur
 Sulfur
5
22.1 There Are Two Major Types of
Biogeochemical Cycles
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 Both gaseous and sedimentary cycles
 Involve biological and nonbiological processes
 Are driven by the flow of energy through the
ecosystem
 Are tied to the water cycle
 Biogeochemical cycles could not exist without the
water cycle.
 All biogeochemical cycles have a common structure
 Inputs
 Internal cycling
 Outputs
6
Fig. 22.1 A generalized representation of the
biogeochemical cycle of an ecosystem. The three
common components– inputs, internal cycling,
and outputs– are shown in bold.
7
22.2 Nutrients Enter the Ecosystem via
Inputs
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 The input of nutrients depends on the cycle.
 Nutrients with a gaseous cycle enter the
ecosystem via the atmosphere.
 Nutrients with a sedimentary cycle enter the
ecosystem via weathering of rocks and
minerals.
8
22.2 Nutrients Enter the Ecosystem via
Inputs
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Supplementing soil nutrients (of terrestrial habitats) are
carried by rain, snow, air currents, and animals.


Wet fall are those nutrients supplied by precipitation.
Dry fall are the nutrients brought in by airborne particles
and aerosols.
The sources of nutrients for aquatic ecosystems


From the surrounding land in the form of drainage water,
detritus, sediment.
Form the atmosphere in precipitation.
9
22.3 Outputs Represent a Loss of
Nutrients from the Ecosystem
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 The output (export) of nutrients depends on the
cycle.
 Release of CO2 from expiration of heterotrophic
organisms.
 Organic matter can be carried out of an ecosystem
 Through surface flow of water or underground
flow of water.
 By herbivores.
 Nutrients are released slowly from organic matter
as it is decomposed.
10
22.3 Outputs Represent a Loss of
Nutrients from the Ecosystem
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 Human harvesting (farming and logging)
 Nutrient loss must be replaced by fertilizers.
 Fire converts a portion of the standing biomass and
soil organic matter to ash.
 Leaching and erosion of soil.
11
22.4 Biogeochemical Cycles Can Be
Viewed from a Global Perspective
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 Often, the output from one ecosystem represents
an input to another.
 The exchange of nutrients among ecosystems
requires us to view the biogeochemical processes
on a broad spatial scale.
 This is particularly true of nutrients that go
through a gaseous cycle.
12
22.5 The Carbon Cycle Is Closely Tied to
Energy Flow
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 Carbon is so closely tied to energy flow that the
two are inseparable.
 Ecosystem productivity = grams C fixed/m2/year
 Inorganic carbon dioxide is the source of all
carbon.
 The inorganic carbon is fixed into the living
component through photosynthesis.
 Carbon dioxide is again released following
respiration.
13
22.5 The Carbon Cycle Is Closely Tied to
Energy Flow
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 Terrestrial cycling of carbon
 Input: photosynthesis
 Output: respiration, decomposition, combustion
 Net primary productivity = carbon uptake
(photosynthesis) – carbon loss (respiration)
 Net ecosystem productivity = difference in
rates
14
22.5 The Carbon Cycle Is Closely Tied to
Energy Flow
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The rate of carbon cycling is determined by the rates of
primary productivity and decomposition.
The rates of primary productivity and decomposition
are directly affected by temperature and precipitation .


In warm, wet ecosystems (e.g., tropical rain forest),
production and decomposition rates are high and carbon
cycles through the ecosystem quickly.
When dead material has not completely decomposed in the
past (e.g., in swamps) the matter has formed fossil fuels.
15
22.5 The Carbon Cycle Is Closely Tied to
Energy Flow
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 Aquatic cycling of carbon
 Input: photosynthesis, diffusion, transport
 Output: respiration, decomposition, diffusion.
 Significant amounts of carbon can be bound as
carbonates incorporated into exoskeletons (e.g.,
shells) of many aquatic organism.
 Carbon dioxide concentration fluctuates
throughout the day
 This is a function of the difference in
photosynthetic activity in response to sunlight
and temperature.
16
Fig. 22.2 The
carbon cycle as
it occurs in
both terrestrial
and aquatic
ecosystems.
17
Fig. 22.3 Daily flux of CO2 in a forest. Note the consistently high level of
CO2 on the forest floor– the site of microbial respiration.
Atmospheric CO2 are highest at night, when photosynthesis shuts down and
respiration pumps CO2 into the atmosphere.
18
22.6 Carbon Cycling Varies Daily and
Seasonally
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The production and use of carbon dioxide fluctuates
with the seasons.

This is a function of temperature and timing of the growing
and dormant seasons.
With the onset of the growing season, the atmospheric
concentration begins to drop as plants withdraw carbon
dioxide through photosynthesis.


The fluctuations are greater in terrestrial environments as
compared to aquatic ecosystems
Fluctuations are much greater in the Northern Hemisphere
due to the larger land area.
19
Fig. 22.4 Variation in atmospheric concentration of CO2 during a
typical year at Barrow, Alaska. Concentrations increase during the
winter months, declining with the onset of photosynthesis during the
growing season (May-June).
20
22.7 The Global Carbon Cycle Involves Exchanges among
the Atmosphere, Oceans, and Land
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 Earth's carbon budget is linked to the
atmosphere, land, and oceans and to the mass
movements of air currents
 The Earth contains 1023 grams (or 100 million
gigatons) of carbon!
 All but a small fraction of this carbon is buried
in sedimentary rock and is not actively
involved in the global carbon cycle.
21
22.7 The Global Carbon Cycle Involves Exchanges
among the Atmosphere, Oceans, and Land
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Carbon pool involved in the global carbon cycle
amounts to 55,000 gigatons (Gt)




Fossil fuels: 10,000 Gt
Oceans: 38,000 Gt (mostly as bicarbonate and carbonate
ions)
 Dead organic matter: 1650 Gt
 Living matter (mostly phytoplankton): 3 Gt
Terrestrial
 Dead organic matter (in soil): 1500 Gt
 Living matter: 560 Gt
Atmosphere: 750 Gt
22
Fig. 22.5 The global carbon cycle,
The sizes of the major pools of
carbon are labelled in red, and arrows
indicate the major exchanges (fluxes)
among them.
23
22.7 The Global Carbon Cycle Involves Exchanges
among the Atmosphere, Oceans, and Land
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The surface water acts as the site of main exchange
of carbon dioxide between atmosphere and ocean

Uptake of CO2 depends on its reaction with carbonate ions
(CO32–) to form bicarbonates (HCO3–)
Carbon circulates physically by means of currents and
biologically through photosynthesis and movement
through the food chain.


Net uptake of carbon in oceans = 1 Gt/year
Net loss of carbon in oceans (due to sedimentation) = 0.5
Gt/year.
24
22.7 The Global Carbon Cycle Involves Exchanges
among the Atmosphere, Oceans, and Land
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 Recent studies suggest that the terrestrial surface
is a carbon sink, with a net uptake of CO2 from
the atmosphere.
 Uptake of CO2 from the atmosphere by
terrestrial systems is determined by
photosynthesis.
 CO2 losses from terrestrial systems are a
function of respiration (especially
decomposition).
25
22.7 The Global Carbon Cycle Involves Exchanges
among the Atmosphere, Oceans, and Land
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 More carbon is stored in soils than in living matter.
 The average carbon/volume of soil increases
from the tropical regions poleward to the boreal
forest and tundra.
 The greatest accumulation of organic
matter occurs in areas where decomposition
is inhibited (e.g., frozen or waterlogged soils)
26
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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 Nitrogen is an essential constituent of protein, a
building block of all living tissue
 Nitrogen is available to plants in two forms
 Ammonium (NH4+)
 Nitrate (NO3–)
 The Earth's atmosphere is 80 percent nitrogen in
the form of N2
 This form is unavailable to plants for
assimilation.
27
Fig. 22.6 The
nitrogen cycle in
terrestrial and
aquatic
ecosystems.
28
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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 Nitrogen enters the ecosystem via two pathways.
1. Atmospheric deposition via wetfall and
dryfall provides nitrogen in a form already
available for plant uptake.
 High-energy fixation occurs when gaseous
nitrogen (N2) is converted to ammonia and
nitrate by energy from cosmic radiation,
meteorite trails, or lightning — this
accounts for only 0.4 kg N/ha annually.
2. Atmospheric nitrogen can be converted into
a usable form biologically — this accounts for
10 kg N/ha annually.
29
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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This fixation is carried out by:



Symbiotic bacteria living in mutualistic
associations with plants.
Free-living aerobic bacteria
Cyanobacteria (blue-green algae)
Nitrogen fixation requires considerable
energy.

To fix 1 g of nitrogen, nitrogen-fixing bacteria
must expend about 10 g of glucose!
30
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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Rhizobium bacteria are symbiotic organisms and form
nodules in the roots of host plants.

Associated with leguminous plants
Free-living soil bacteria (Azotobacter, Clostridium)
are prominent in converting nitrogen into a usable form.
Cyanobacteria (Nostoc, Calothrix) fix nitrogen in
terrestrial and aquatic ecosystems.
Certain lichens may also fix nitrogen.
31
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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 Ammonification occurs when ammonium (NH4+) is
converted to NH3 as a waste product of microbial activity.
 Loss of gaseous NH3 from the soil to the atmosphere is
influenced by soil pH.
 Nitrification is the stepwise conversion of NH4+ to NO2–
(by Nitrosomonas) and then conversion of NO2– to NO3–
(by Nitrobacter).
 Denitrification is the chemical reduction of NO3– to N2O
and N2 (by Pseudomonas) which are then returned to the
atmosphere
32
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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 Nitrification is the stepwise conversion of NH4+ to NO2– (by
Nitrosomonas) and then conversion of NO2– to NO3– (by
Nitrobacter).
 The nitrate may be taken up by plant roots or returned to the
atmosphere.
 Denitrification is the chemical reduction of NO3– to N2O and N2
(by Pseudomonas) which are then returned to the atmosphere
 This reduction requires anaerobic conditions
 This process is common in wetland ecosystems and bottom
sediments of aquatic ecosystems
33
Fig. 22.7 Bacterial processes involved in nitrogen cycling.
34
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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 Nitrate is the most common form of nitrogen
exported from terrestrial ecosystems in stream
water.
 The amount of nitrogen recycled is usually much
greater than inputs or outputs of nitrogen.
 Nitrogen fixation and nitrification are influenced
by environmental conditions.
 Bacterial activity is affected by temperature,
moisture, and soil pH.
 In highly acidic soils, bacterial action is inhibited.
35
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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 The internal cycling of nitrogen is fairly similar
from ecosystem to ecosystem
 Assimilation of NH4+ and NO3– by plants
 Return of nitrogen to the soil, sediments, and
water via decomposition.
 The nitrogen pool
 Atmosphere: 3.9 × 1021 g
 Terrestrial
 Biomass: 3.5 × 1015 g
 Soils: 95 × 1015 to 140 × 1015 g
36
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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 Nitrogen loss
 Terrestrial and aquatic denitrification: 200 × 1012
g/yr
 Sedimentation
 Nitrogen input
12 g/yr
 Freshwater drainage: 36 × 10
 Precipitation: 30 × 1012 g/yr
12 g/yr
 Biological fixation: 15 × 10
37
38
Fig. 22.8 The global nitrogen cycle, Each
flux is shown in units of 1012 g N/yr.
22.8 The Nitrogen Cycle Begins with
Fixing Atmospheric Nitrogen
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 Human activity has significantly influenced the global nitrogen
cycle.
 Conversion of native forests and grasslands to agricultural
fields.
 Application of chemical fertilizers to agricultural fields.
 Auto exhaust and combustion add N2O, NO, and NO2 to the
atmosphere, which leads to an increase in ozone
concentration of the stratosphere.
39
22.9 The Phosphorus Cycle Has No
Atmospheric Pool
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 Phosphorus (P) can only be cycled from land to
sea and is not returned via the biogeochemical
cycle.
 The main reservoirs of P are rock and natural
phosphate deposits.
 Phosphorus is released by weathering, leaching,
erosion, and mining.
 In most soils, only a small fraction of total
phosphorus is available to plants.
40
Fig. 22.9 The phosphorus cycle in aquatic and terrestrial ecosystems.
41
22.9 The Phosphorus Cycle Has No
Atmospheric Pool
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 In freshwater and marine ecosystems, the
phosphorus cycle moves through three states
 Particulate organic phosphorus (PP)
 Dissolved organic phosphates (PO)
 Inorganic phosphates (Pi)
42
22.9 The Phosphorus Cycle Has No
Atmospheric Pool
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Organic phosphates are taken in by all forms of
phytoplankton, which are eaten by zooplankton.
Zooplankton may excrete as much phosphorus daily as
it stores in its biomass.
Some phosphorus is deposited in sediments  surface
waters may become depleted while the deep waters
become saturated.

This phosphorus can be returned to the surface waters and
accessed by organisms when upwelling occurs.
43
22.9 The Phosphorus Cycle Has No
Atmospheric Pool
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 The phosphorus cycle
 Little atmospheric component although airborne transport of
~1 × 1012 g P/yr
 River transport = 21 × 1012 g P/yr (only 10 percent is
available for NPP)
 Ocean waters are a significant global pool of P simply due to
large volume.
 Organic phosphorus in the surface waters is recycled very
rapidly.
 The phosphorous deposited in sediments or deep waters is
unavailable to phytoplankton until upwelling.
44
45
Fig. 22.10 The global phosphorus cycle. Each flux is shown in
units of 1012 g P/yr.
Ecological Issues Nitrogen Saturation
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 NPP in most terrestrial forest ecosystems is limited
by soil nitrogen availability.
 Anthropogenic activity and high-intensity
agriculture have increased inputs of nitrogen
oxides in the atmosphere far above natural inputs.
 Generally, nitrogen is deposited in the region
where it originated and thus will vary with
geography and human population density.
46
Fig. 1 Estimated inorganic nitrogen deposition from nitrate and
ammonium in 1998.
47
Ecological Issues Nitrogen Saturation
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 Soil nitrogen concentration influences the rate of N
uptake and plant tissue concentration.
 Up to a point, as nitrogen concentration increases,
net primary productivity increases.
 As the ecosystem approaches "nitrogen
saturation," the soil and plant community suffer
negative impacts.
 Release of other important soil cations (e.g., Mg)
as ammonium concentration increases.
 Soil acidification that may contribute to toxic
levels of aluminum ions.
48
Fig. 2 Hypothesized response of temperate forest ecosystems to long-term
nitrogen additions. In stage 1, N-mineralization increases, which results in
increased NPP. In stage 2, NPP and N-mineralization decline due to
decreasing Ca:Al and Mg:N ratios and to soil acidification. Nitrification also
increases as excess ammonium is available. Finally, in stage 3, nitrate leaching
increases dramatically.
49
22.10 The Sulfur Cycle Is Both
Sedimentary and Gaseous
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 The sulfur cycle has both sedimentary and
gaseous phases.
 In the long-term sedimentary phase, sulfur is
tied up in organic and inorganic deposits and is
released by weathering and decomposition.
 The gaseous phase permits sulfur to circulate on
a global scale.
50
Fig. 22.12 The sulfur cycle. Note the two components:
sedimentary and gaseous. Major sources from human activity are
the burning of fossil fuels and acidic drainage from coal mines.
51
22.10 The Sulfur Cycle Is Both
Sedimentary and Gaseous
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 Atmospheric sulfur sources (as H2S)
 Combustion of fossil fuels
 Volcanic eruptions
 Ocean surface exchange
 Decomposition
 Atmospheric sulfur dioxide (SO2) is carried back to
the surface in rainwater as weak sulfuric acid
(H2SO4)
52
22.10 The Sulfur Cycle Is Both
Sedimentary and Gaseous
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 Sulfur is incorporated into plants via
photosynthesis and building of sulfur-bearing
amino acids.
 Excretion and death return sulfur from living
material back to the soil and sediments.
 Bacteria release it as hydrogen sulfite or sulfate
 Colorless, green, and purple bacteria each have
a unique interaction with sulfur.
53
22.10 The Sulfur Cycle Is Both
Sedimentary and Gaseous
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 Pyritic rocks (硫化鐵礦)(those that contain FeS) can
be a source of sulfur if weathered or uncovered by
humans (during coal mining).
 These products (e.g., sulfuric acid) can be
extremely detrimental to aquatic ecosystems.
 The annual flux of sulfur compounds (SO2, H2S,
sulfate particles) through the atmosphere ~300 ×
1012 g
 Wetfall and dryfall of sulfate particles
54
22.11 The Global Sulfur Cycle Is Poorly
Understood
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 Oceans are a large source sulfate aerosols, though
most are redeposited in precipitation and dryfall.
 Dimethylsulfide [(CH3)2S] is the major sulfur gas
emitted (16 × 1012 g S/yr) from the oceans and
is generated by biological processes.
 H2S is the dominant sulfur form emitted from
freshwater wetlands and anoxic soils.
 Forest fires emit 3 × 1012 g S annually.
 Volcanic activity contributes to the global cycle of
sulfur.
55
Fig. 22.12 The global
sulfur cycle. Each flux
is shown in units of
1012 g S/yr.
56
22.12 The Oxygen Cycle Is Largely
Under Biological Control
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 The major source of oxygen (O2) that supports life is the
atmosphere and may originate from two processes
+
 Breakup of water vapor = 2 H2O  O2 + 4 H
 Photosynthetic production
 The input of oxygen must have exceeded its loss (due to
respiration) for an overall abundance of oxygen.
 Water and carbon dioxide are other sources of oxygen.
 Oxygen is also biologically exchangeable in various molecules
that are transformed by living organisms (e.g., hydrogen sulfide
to sulfates).
57
Fig. 22.13 A simple model for
the global biogeochemical
cycle of O2. Data are
expressed in units of 1012
moles of O2 per year or the
equivalent amount of reduced
compounds. Note that a small
misbalance in the ratio of
photosynthesis to respiration
can result in a net storage of
reduced organic materials in
the crust and an accumulation
of O2 in the atmosphere.
58
22.12 The Oxygen Cycle Is Largely
Under Biological Control
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 Due to oxygen's reactivity, its cycling in the ecosystem is
complex.
 Carbon dioxide + calcium  carbonates
 Nitrogen compounds  nitrates
 Iron compounds  ferric oxides
 Ozone (O3) is an atmospheric gas
 In the stratosphere (10 to 40 km above Earth) it acts as a UV
shield
 Close to the ground, it is a pollutant
59
22.12 The Oxygen Cycle Is Largely
Under Biological Control
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 In the stratosphere, O2 is freed by solar radiation and freed
oxygen atoms rapidly combine with O2 to form O3 (this reaction
is reversible).
 Under natural conditions, a balance exists between ozone
formation and destruction.
 Human activity has interrupted this balance, and various
molecules (e.g., CFCs) reduce the production of O3
60
22.13 The Various Biogeochemical
Cycles Are Linked
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 The biogeochemical cycles are linked through their common
membership in compounds that form an important component of
their cycles
 Nitrate and oxygen in nitrate
 Autotrophs and heterotrophs require nutrients in different
proportions for different processes
 Stoichiometry (化學計量學) is the branch of chemistry that
deals with the quantitative relationships of elements in
combination.
61
Chap.22 Biogeochemical cycles
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