chapter 7: pathways of elements in the ecosystem

Chapter 7: Chapter 7: Pathways of Pathways of

Elements in the Elements in the EcosystemEcosystem

Robert E. RicklefsRobert E. Ricklefs

The Economy of Nature, Fifth EditionThe Economy of Nature, Fifth Edition

BackgroundBackground

Cycling of elements and flux of energy in Cycling of elements and flux of energy in ecosystems are fundamentally different:ecosystems are fundamentally different: chemical elements are reused repeatedlychemical elements are reused repeatedly energy flows through the system only onceenergy flows through the system only once

Many aspects of elemental cycling make Many aspects of elemental cycling make sense only when we understand that sense only when we understand that chemical transformations and energy chemical transformations and energy transformations go hand in hand.transformations go hand in hand.

(c) 2001 by W. H. Freeman and Company

Assimilatory and Assimilatory and Dissimilatory ProcessesDissimilatory Processes

Assimilatory processes:Assimilatory processes: incorporate inorganic forms of elements into incorporate inorganic forms of elements into

organic forms, requiring energyorganic forms, requiring energy example: photosynthesis (reduction of example: photosynthesis (reduction of

carbon)carbon)

Dissimilatory processes:Dissimilatory processes: transform organic forms of elements into transform organic forms of elements into

inorganic forms, releasing energyinorganic forms, releasing energy example: respiration (oxidation of carbon)example: respiration (oxidation of carbon)


Energy transformations and Energy transformations and element cycling are linked.element cycling are linked.

Organisms play important roles in cycling of Organisms play important roles in cycling of elements when they carry out chemical elements when they carry out chemical transformations:transformations: most biological energy transformations are most biological energy transformations are

associated with biochemical oxidation and associated with biochemical oxidation and reduction of C, O, N, and Sreduction of C, O, N, and S

these assimilatory and dissimilatory these assimilatory and dissimilatory processes are often linked, one providing processes are often linked, one providing energy for the otherenergy for the other


Coupled reactions are the basis of Coupled reactions are the basis of energy flow in ecosystems.energy flow in ecosystems.

A typical coupling of assimilatory/ A typical coupling of assimilatory/ dissimilatory reactions might involve:dissimilatory reactions might involve: oxidation (dissimilation) of carbon in oxidation (dissimilation) of carbon in

carbohydrate (energy-yielding), linked tocarbohydrate (energy-yielding), linked to reduction (assimilation) of nitrate-N to amino-reduction (assimilation) of nitrate-N to amino-

N (energy-requiring)N (energy-requiring)

Some processes may involve many steps.Some processes may involve many steps.

Energy is lost at each step (inefficiency).Energy is lost at each step (inefficiency).


Ecosystems may be modeled as Ecosystems may be modeled as linked compartments.linked compartments.

An ecosystem may be viewed as a set of An ecosystem may be viewed as a set of compartments among which elements are compartments among which elements are cycled at various rates:cycled at various rates: photosynthesis moves carbon from an photosynthesis moves carbon from an

inorganic compartment (air or water) to an inorganic compartment (air or water) to an organic compartment (plant)organic compartment (plant)

respiration moves carbon from an organic respiration moves carbon from an organic compartment (organism) to an inorganic compartment (organism) to an inorganic compartment (air or water)compartment (air or water)


Elements move among Elements move among compartments at different rates.compartments at different rates.

Inorganic carbon released through Inorganic carbon released through respiration may be taken up quickly respiration may be taken up quickly through photosynthesis. The organic through photosynthesis. The organic carbon fixed may be respired again quickly carbon fixed may be respired again quickly by plants.by plants.

Organic carbon stored in deposits of coal, Organic carbon stored in deposits of coal, oil, or peat is not readily accessible and oil, or peat is not readily accessible and may remain in storage for millions of years.may remain in storage for millions of years.

Inorganic carbon may also be taken out of Inorganic carbon may also be taken out of circulation for millions of years by circulation for millions of years by precipitation as calcium carbonate in precipitation as calcium carbonate in aquatic systems.aquatic systems.


A Physical Model for the A Physical Model for the Water CycleWater Cycle

The biosphere contains 1,400,000 The biosphere contains 1,400,000 teratons (TT, 10teratons (TT, 101212 metric tons) of water, metric tons) of water, 97% of which resides in the oceans.97% of which resides in the oceans.

Other water compartments include:Other water compartments include: ice caps and glaciers (29,000 TT)ice caps and glaciers (29,000 TT) underground aquifers (8,000 TT)underground aquifers (8,000 TT) lakes and rivers (100 TT)lakes and rivers (100 TT) soil moisture (100 TT)soil moisture (100 TT) water in atmosphere (13 TT)water in atmosphere (13 TT) water in living things (1 TT)water in living things (1 TT)


The water cycle is solar-The water cycle is solar-powered.powered.

The water cycle consumes one-fourth of the The water cycle consumes one-fourth of the total solar energy striking the earth during total solar energy striking the earth during a year:a year: precipitation over land exceeds evaporation precipitation over land exceeds evaporation

by 40 teratons/yr; surplus returns to the by 40 teratons/yr; surplus returns to the ocean in riversocean in rivers

evaporation over the oceans exceeds evaporation over the oceans exceeds precipitation by 40 teratons/yr; surplus is precipitation by 40 teratons/yr; surplus is delivered by winds to the land massesdelivered by winds to the land masses


The residence time of water varies The residence time of water varies by compartment.by compartment.

The atmosphere contains 2.5 cm of The atmosphere contains 2.5 cm of moisture at any time; annual flux into moisture at any time; annual flux into and out of the atmosphere is 65 cm/yr:and out of the atmosphere is 65 cm/yr: residence time is compartment size/flux, or residence time is compartment size/flux, or

2.5 cm / 65 cm/yr = 0.04 yr, about 2 weeks.2.5 cm / 65 cm/yr = 0.04 yr, about 2 weeks.

Soils, rivers, lakes and oceans have Soils, rivers, lakes and oceans have same flux rates as atmosphere, but same flux rates as atmosphere, but they contain about 100,000 times as they contain about 100,000 times as much water, yielding a mean residence much water, yielding a mean residence time of 2,800 yrtime of 2,800 yr..


The carbon cycle is linked The carbon cycle is linked to global energy flux.to global energy flux.

The carbon cycle is the focal point of The carbon cycle is the focal point of biological energy transformations.biological energy transformations.

Principal classes of carbon-cycling Principal classes of carbon-cycling processes:processes: assimilatory/dissimilatory processes assimilatory/dissimilatory processes

(mainly photosynthesis and respiration)(mainly photosynthesis and respiration) exchange of COexchange of CO22 between atmosphere and between atmosphere and

oceansoceans sedimentation of carbonatessedimentation of carbonates


Photosynthesis and Photosynthesis and RespirationRespiration

Approximately 85 GT of carbon enter into Approximately 85 GT of carbon enter into balanced assimilatory/dissimilatory balanced assimilatory/dissimilatory transformations each year.transformations each year.

Total global carbon in organic matter is Total global carbon in organic matter is about 2,650 GT (living organisms plus about 2,650 GT (living organisms plus organic detritus and sediments).organic detritus and sediments).

Residence time for carbon in biological Residence time for carbon in biological molecules = 2,650 GT / 85 GT/yr = 31 yr.molecules = 2,650 GT / 85 GT/yr = 31 yr.


Ocean-Atmosphere Ocean-Atmosphere ExchangeExchange

Exchange of carbon across the atmosphere-Exchange of carbon across the atmosphere-ocean interface links carbon cycles of ocean interface links carbon cycles of terrestrial and aquatic ecosystems.terrestrial and aquatic ecosystems.

Dissolved carbon pool is 30,000 GT, nearly Dissolved carbon pool is 30,000 GT, nearly 50 X that of atmosphere (640 GT).50 X that of atmosphere (640 GT).

Net atmospheric flux (assimilation/ Net atmospheric flux (assimilation/ dissimilation and exchange with oceans) is dissimilation and exchange with oceans) is 119 GT/yr for mean atmospheric residence 119 GT/yr for mean atmospheric residence time (640 GT / 119 GT/yr) of about 5 years.time (640 GT / 119 GT/yr) of about 5 years.


Precipitation of Precipitation of CarbonatesCarbonates

Precipitation (and dissolution) of Precipitation (and dissolution) of carbonates occurs in aquatic systems:carbonates occurs in aquatic systems: precipitation (as calcium and magnesium precipitation (as calcium and magnesium

carbonates) leads to formation of limestone carbonates) leads to formation of limestone and dolomite rockand dolomite rock turnover of these sediments is far slower than turnover of these sediments is far slower than

those associated with assimilation/dissimilation those associated with assimilation/dissimilation or ocean-atmosphere exchangeor ocean-atmosphere exchange

carbonate sediments represent the single carbonate sediments represent the single largest compartment of carbon on planet largest compartment of carbon on planet (18,000,000 GT)(18,000,000 GT)


Precipitation of Calcium and Precipitation of Calcium and Carbon Through the AgesCarbon Through the Ages

COCO22 dissolves in water to form carbonic dissolves in water to form carbonic acid, which dissociates into hydrogen, acid, which dissociates into hydrogen, bicarbonate, and carbonate ions:bicarbonate, and carbonate ions:

COCO22 + H + H22O O H H22COCO33

HH22COCO33 H H++ + HCO + HCO33-- 2H 2H++ + CO + CO33

2-2-

Calcium ions combine with carbonate Calcium ions combine with carbonate ions to form slightly insoluble calcium ions to form slightly insoluble calcium carbonate, which precipitates:carbonate, which precipitates:

CaCa2+2+ + CO + CO332-2- CaCO CaCO33


Slow Release of Sedimentary Slow Release of Sedimentary Calcium and CarbonCalcium and Carbon

Calcium removed from the water column in Calcium removed from the water column in the oceans is replaced by calcium dissolved the oceans is replaced by calcium dissolved from limestone sediments on land by from limestone sediments on land by slightly acidic water of rivers and streams.slightly acidic water of rivers and streams.

Carbon is also slowly released from oceanic Carbon is also slowly released from oceanic sediments as limestone is subducted sediments as limestone is subducted beneath continental plates, and CObeneath continental plates, and CO22 is is outgassed in volcanic eruptions.outgassed in volcanic eruptions.


Reef-Builders extract Reef-Builders extract carbon from water.carbon from water.

In neutral conditions of marine ecosystems, In neutral conditions of marine ecosystems, extraction of COextraction of CO22 from water column drives from water column drives precipitation of CaCOprecipitation of CaCO33::

CaCOCaCO33 + H + H22O + COO + CO22 Ca Ca2+2+ + 2HCO + 2HCO33--

Reef-building algae and coralline algae Reef-building algae and coralline algae incorporate calcium carbonate into their incorporate calcium carbonate into their hard structures, forming reefs.hard structures, forming reefs.


Changes in the Carbon Changes in the Carbon Cycle Over TimeCycle Over Time

Atmospheric COAtmospheric CO22 concentrations have concentrations have varied considerably over earth’s history:varied considerably over earth’s history: during the early Paleozoic era (550-400 Mya), during the early Paleozoic era (550-400 Mya),

concentrations were 15-20 X those at presentconcentrations were 15-20 X those at present concentrations declined to ca. present level by concentrations declined to ca. present level by

300 Mya, then increased again to 5 X present 300 Mya, then increased again to 5 X present level through the early Mesozoic era (250-150 level through the early Mesozoic era (250-150 Mya) and have declined gradually sinceMya) and have declined gradually since

early Paleozoic and early Mesozoic eras were early Paleozoic and early Mesozoic eras were extreme greenhouse times, unlikely to be extreme greenhouse times, unlikely to be equaled by effects of current human equaled by effects of current human enhancement of atmospheric COenhancement of atmospheric CO22


Nitrogen - A Most Nitrogen - A Most Versatile Element!Versatile Element!

Ultimate source (largest reservoir) of this Ultimate source (largest reservoir) of this essential element is molecular Nessential element is molecular N22 gas in the gas in the atmosphere, which can also dissolve in water atmosphere, which can also dissolve in water to some extent.to some extent.

Nitrogen is absent from native rock.Nitrogen is absent from native rock.

Nitrogen enters biological pathways through Nitrogen enters biological pathways through nitrogen fixation:nitrogen fixation: these pathways are more complicated than those these pathways are more complicated than those

of the carbon cycle because nitrogen has more of the carbon cycle because nitrogen has more oxidized and reduced forms than carbonoxidized and reduced forms than carbon


AmmonificationAmmonification

Plants assimilate inorganic nitrogen into Plants assimilate inorganic nitrogen into proteins, which may be passed through proteins, which may be passed through various trophic levels.various trophic levels.

Ammonification (dissimilation of N) is Ammonification (dissimilation of N) is carried out by all organisms:carried out by all organisms: initial step is breakdown of proteins into initial step is breakdown of proteins into

constituent amino acids by hydrolysisconstituent amino acids by hydrolysis carbon (not nitrogen) in amino acids is then carbon (not nitrogen) in amino acids is then

oxidized, releasing ammonia (NHoxidized, releasing ammonia (NH33))


NitrificationNitrification

Nitrification is oxidation of ammonia:Nitrification is oxidation of ammonia: first step is oxidation of ammonia to nitrite first step is oxidation of ammonia to nitrite

(NO(NO22--), carried out by ), carried out by NitrosomonasNitrosomonas in soil and in soil and

NitrosococcusNitrosococcus in oceans in oceans nitrite is then oxidized to nitrate (NOnitrite is then oxidized to nitrate (NO33

--) by ) by NitrobacterNitrobacter in soil and in soil and NitrococcusNitrococcus in oceans in oceans

nitrification is an aerobic process; the nitrification is an aerobic process; the nitrifying organisms involved are nitrifying organisms involved are chemoautotrophic bacteriachemoautotrophic bacteria


DenitrificationDenitrification

Denitrification is the reduction of nitrate to Denitrification is the reduction of nitrate to nitric oxide (NO), which escapes as a gas:nitric oxide (NO), which escapes as a gas: occurs in waterlogged, anaerobic soils, oxygen-occurs in waterlogged, anaerobic soils, oxygen-

depleted sediments, and bottom waters in depleted sediments, and bottom waters in aquatic ecosystemsaquatic ecosystems

carried out by heterotrophic bacteria such as carried out by heterotrophic bacteria such as Pseudomonas denitrificansPseudomonas denitrificans

further N-reductions may lead to production of further N-reductions may lead to production of nitrous oxide (Nnitrous oxide (N22O) and molecular nitrogen (NO) and molecular nitrogen (N22), ), both gasesboth gases

denitrification may be one of the principal causes denitrification may be one of the principal causes of low availability of nitrogen in marine systemsof low availability of nitrogen in marine systems


Nitrogen FixationNitrogen Fixation

Loss of nitrogen to atmosphere by Loss of nitrogen to atmosphere by denitrification is offset by nitrogen fixation:denitrification is offset by nitrogen fixation: fixation is carried out by:fixation is carried out by:

free-living bacteria such as free-living bacteria such as AzotobacterAzotobacter symbiotic bacteria such as symbiotic bacteria such as RhizobiumRhizobium, living in root , living in root

nodules of legumes and other plantsnodules of legumes and other plants cyanobacteriacyanobacteria

N-fixation is an energy-requiring process, with N-fixation is an energy-requiring process, with energy supplied by oxidation of organic detritus energy supplied by oxidation of organic detritus (free-living bacteria), sugars supplied by plants (free-living bacteria), sugars supplied by plants (bacterial symbionts), or photosynthesis (bacterial symbionts), or photosynthesis (cyanobacteria)(cyanobacteria)


Significance of Significance of Nitrogen FixationNitrogen Fixation

Nitrogen fixation balances denitrification on Nitrogen fixation balances denitrification on a global basis:a global basis: these fluxes amount to about 2% of total these fluxes amount to about 2% of total

cycling of nitrogen through ecosystemscycling of nitrogen through ecosystems

Nitrogen fixation is often very important on Nitrogen fixation is often very important on a local scale:a local scale: N-fixers dominate early colonizers on N-fixers dominate early colonizers on

nitrogen-poor substrates, such as lava flows nitrogen-poor substrates, such as lava flows or areas left bare by receding glaciersor areas left bare by receding glaciers


The Phosphorus CycleThe Phosphorus Cycle

Phosphorous is an essential element, Phosphorous is an essential element, constituent of nucleic acids, cell constituent of nucleic acids, cell membranes, energy transfer systems, membranes, energy transfer systems, bones, and teeth.bones, and teeth.

Phosphorus may limit productivity:Phosphorus may limit productivity: in aquatic systems, sediments act as a in aquatic systems, sediments act as a

phosphorus sink unless oxygen-depletedphosphorus sink unless oxygen-depleted in soils, phosphorus is only readily available in soils, phosphorus is only readily available

between pH of 6 and 7between pH of 6 and 7


Phosphorus Phosphorus TransformationsTransformations

Phosphorus undergoes relatively few Phosphorus undergoes relatively few transformations:transformations: plants assimilate P as phosphate (POplants assimilate P as phosphate (PO44

3-3-) and ) and incorporate this into organic compoundsincorporate this into organic compounds

animals and phosphatizing bacteria break animals and phosphatizing bacteria break down organic forms of phosphorus and release down organic forms of phosphorus and release the phosphorus as phosphatethe phosphorus as phosphate

phosphorus does not:phosphorus does not: undergo oxidation-reduction reactions in the undergo oxidation-reduction reactions in the

ecosystemecosystem circulate through the atmosphere, except as dustcirculate through the atmosphere, except as dust


The Sulfur Cycle 1The Sulfur Cycle 1

Sulfur is an essential element and, like Sulfur is an essential element and, like nitrogen, has many oxidation states and nitrogen, has many oxidation states and follows complex chemical pathways.follows complex chemical pathways.

Sulfur reduction reactions include:Sulfur reduction reactions include: assimilatory sulfate reduction to organic assimilatory sulfate reduction to organic

forms and dissimilatory oxidation back to forms and dissimilatory oxidation back to sulfate by many organismssulfate by many organisms

reduction of sulfate when used as an reduction of sulfate when used as an oxidizer for respiration by heterotrophic oxidizer for respiration by heterotrophic bacteria in anaerobic environmentsbacteria in anaerobic environments


The Sulfur Cycle 2The Sulfur Cycle 2

Sulfur oxidation reactions include:Sulfur oxidation reactions include: oxidation of reduced sulfur when used as an oxidation of reduced sulfur when used as an

electron donor (in place of oxygen in water) electron donor (in place of oxygen in water) by photosynthetic bacteriaby photosynthetic bacteria

oxidation of sulfur by chemoautotrophic oxidation of sulfur by chemoautotrophic bacteria that use the energy thus obtained for bacteria that use the energy thus obtained for assimilation of COassimilation of CO22


Sulfur in Coal and Oil Sulfur in Coal and Oil DepositsDeposits

Iron sulfide (FeS) commonly associated with Iron sulfide (FeS) commonly associated with coal and oil deposits can result in coal and oil deposits can result in environmental problems:environmental problems: oxidation of sulfides in mine wastes to oxidation of sulfides in mine wastes to

sulfate, which combines with water to form sulfate, which combines with water to form sulfuric acid, associated with acid mine sulfuric acid, associated with acid mine drainagedrainage

oxidation of sulfides in coal and oil releases oxidation of sulfides in coal and oil releases sulfates into atmosphere, which then form sulfates into atmosphere, which then form sulfuric acid, a component of acid rainsulfuric acid, a component of acid rain


Microorganisms assume diverse Microorganisms assume diverse roles in element cycles.roles in element cycles.

Decomposition in anaerobic organic Decomposition in anaerobic organic sediments is dependent on certain sediments is dependent on certain specialized microbes, the denitrifiers:specialized microbes, the denitrifiers:

these heterotrophic organisms use oxidized these heterotrophic organisms use oxidized forms of N, S, and Fe as electron acceptors forms of N, S, and Fe as electron acceptors (oxidizers) in the absence of oxygen(oxidizers) in the absence of oxygen

for example, some anaerobic bacteria utilize for example, some anaerobic bacteria utilize nitrate as an alternative electron acceptor for nitrate as an alternative electron acceptor for the oxidation of glucose:the oxidation of glucose:

glucose + NOglucose + NO33-- CO CO22 + H + H22O + OHO + OH-- + N + N22 + energy + energy


Biological Nitrogen Biological Nitrogen FixationFixation

Biological nitrogen fixation (by bacteria and Biological nitrogen fixation (by bacteria and cyanobacteria) is essential to cyanobacteria) is essential to counterbalancing N losses associated with counterbalancing N losses associated with denitrification.denitrification.

Nitrogen is often implicated as a limiting Nitrogen is often implicated as a limiting nutrient in terrestrial and aquatic systems.nutrient in terrestrial and aquatic systems.

Nitrogen fixation is critical to ecosystem Nitrogen fixation is critical to ecosystem development in primary succession.development in primary succession.

Continued nitrogen input is essential for Continued nitrogen input is essential for long-term health of natural ecosystems.long-term health of natural ecosystems.


Autotrophic DiversityAutotrophic Diversity

All autotrophs are capable of assimilating All autotrophs are capable of assimilating (reducing) carbon in CO(reducing) carbon in CO22 into organic forms into organic forms (initially glucose):(initially glucose): photoautotrophs accomplish this by capturing photoautotrophs accomplish this by capturing

energy from sun through photosynthesis:energy from sun through photosynthesis: green plants, algae, and cyanobacteria use green plants, algae, and cyanobacteria use

water as an electron donor (reducing agent) and water as an electron donor (reducing agent) and are aerobicare aerobic

purple and green bacteria use Hpurple and green bacteria use H22S or organic S or organic compounds as electron donors and are compounds as electron donors and are anaerobicanaerobic


ChemoautotrophsChemoautotrophsChemoautrophs are not photosynthetic, Chemoautrophs are not photosynthetic,

reducing inorganic carbon (from COreducing inorganic carbon (from CO22), but ), but using energy obtained from aerobic using energy obtained from aerobic oxidation of inorganic substrates:oxidation of inorganic substrates: methane - methane - Methanosomonas, MethylomonasMethanosomonas, Methylomonas hydrogen - hydrogen - Hydrogenomonas, MicrococcusHydrogenomonas, Micrococcus ammonia - nitrifying bacteria ammonia - nitrifying bacteria Nitrosomonas, Nitrosomonas,

NitrococcusNitrococcus nitrite - nitrifying bacteria nitrite - nitrifying bacteria Nitrobacter, Nitrobacter,

NitrococcusNitrococcus hydrogen sulfide, sulfur, sulfate - hydrogen sulfide, sulfur, sulfate - ThiobacillusThiobacillus ferrous iron salts - ferrous iron salts - Ferrobacillus, GallionellaFerrobacillus, Gallionella


Deep-Sea Vent Deep-Sea Vent EcosystemsEcosystems

Deep-sea vent ecosystems are far below Deep-sea vent ecosystems are far below the penetration of any light, dependent the penetration of any light, dependent on chemoautotrophic production:on chemoautotrophic production: hot water coming from vents is charged with hot water coming from vents is charged with

hydrogen sulfide, Hhydrogen sulfide, H22SS chemoautrophic bacteria use oxygen from chemoautrophic bacteria use oxygen from

seawater to oxidize Hseawater to oxidize H22S, then use the energy S, then use the energy thus obtained for assimilatory carbon thus obtained for assimilatory carbon reductionreduction

other members of vent communities (clams, other members of vent communities (clams, worms, crabs, fish) ultimately depend on worms, crabs, fish) ultimately depend on primary production of these bacteriaprimary production of these bacteria


Living things are intimately Living things are intimately involved in elemental cycles.involved in elemental cycles.

Elements are cycled through ecosystems Elements are cycled through ecosystems primarily because metabolic activities primarily because metabolic activities result in chemical transformations.result in chemical transformations.

Each type of habitat presents a different Each type of habitat presents a different chemical environment, especially with chemical environment, especially with respect to:respect to: presence/absence of oxygenpresence/absence of oxygen possible sources of energypossible sources of energy

Numerous adaptations have arisen to Numerous adaptations have arisen to meet these challenges.meet these challenges.


Summary 1Summary 1

Unlike energy, nutrients are retained in Unlike energy, nutrients are retained in ecosystems and may cycle indefinitely.ecosystems and may cycle indefinitely.

The movements of energy and elements, The movements of energy and elements, especially carbon, parallel one another in especially carbon, parallel one another in ecosystems.ecosystems.

Energy transformations result from the Energy transformations result from the coupled oxidation and reduction reactions coupled oxidation and reduction reactions of various elements.of various elements.


Summary 2Summary 2

The water cycle is a physical analogy for The water cycle is a physical analogy for element cycling in ecosystems; many elements element cycling in ecosystems; many elements are also transported by the water cycle.are also transported by the water cycle.

The carbon cycle involves both biological and The carbon cycle involves both biological and nonbiological processes fundamental to nonbiological processes fundamental to functioning of the biosphere.functioning of the biosphere.

The nitrogen cycle involves many The nitrogen cycle involves many transformations and oxidation states. transformations and oxidation states. Microorganisms play essential roles throughout.Microorganisms play essential roles throughout.


chapter 7: pathways of elements in the ecosystem

Documents

inorganic carbon

inorganic forms of elements

chemical elements

water compartments

carbohydrate energy

flux of energy

inorganic compartment

chemical transformations