NUTRIENT CYCLES
Prof. Murray, Univ of Illinois at Chicago
NUTRIENT CYCLES: ECOSYSTEM TO
ECOSPHERE
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Nutrient cycling occurs at the
local level through the action
of the biota.
Nutrient cycling occurs at the
global level through geological
processes, such as,
atmospheric circulation,
erosion and weathering.
NUTRIENT CYCLES
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The atoms of earth and life are the same; they just find
themselves in different places at different times.
Most of the calcium in your bones came from cows,
who got it from corn, which took it from rocks that
were once formed in the sea.
The path atoms take from the living (biotic) to the
non-living (abiotic) world and back again is called a
biogeochemical cycle.
Nutrients: The Elements of Life
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Of the 50 to 70 atoms
(elements) that are found
in living things, only 15 or
so account for the major
portion of living biomass.
Only around half of these
15 have been studied
extensively as they travel
through ecosystems or
circulate on a global scale.
O OXYGEN
K POTASSIUM
P PHOSPHORUS
C CARBON
Si SILICON
Cl CHLORINE
H HYDROGEN
Mg MAGNESIUM
Fe IRON
N NITROGEN
S SULFUR
Mn MANGANESE
Ca CALCIUM
Al ALUMINUM
Na SODIUM
A GENERALIZED MODEL OF
NUTRIENT CYCLING IN AN
ECOSYSTEM
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The cycling of nutrients in an
ecosystem are interlinked by
an a number of processes that
move atoms from and
through organisms and to and
from the atmosphere, soil
and/or rocks, and water.
Nutrients can flow between
these compartments along a
variety of pathways.
Nutrient Compartments in a Terrestrial
Ecosystem
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The organic compartment consists of the living
organisms and their detritus.
The available-nutrient compartment consists of
nutrients held to surface of soil particles or in
solution.
The third compartment consists of nutrients held in
soils or rocks that are unavailable to living organisms.
The fourth compartment is the air which can be
found in the atmosphere or in the ground.
Uptake of Inorganic Nutrients from
the Soil
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With the exception of CO2 and O2
which enter though leaves, the
main path of all other nutrients is
from the soil through the roots of
producers.
Even consumers which find Ca, P, S
and other elements in the water
they drink, obtain the majority of
these nutrients either directly or
indirectly from producers.
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E.g. you get calcium from milk which
came from the diet of the cow –
producers.
The Atmosphere Is a Source of
Inorganic Nutrients
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The atmosphere acts as a
reservoir for carbon dioxide
(CO2), oxygen (O2) and water
(H2O).
These inorganic compounds can
be exchanged directly with the
biota through the processes of
photosynthesis and respiration.
The most abundant gas in the
atmosphere is nitrogen
(N2);about 80% by volume. Its
entry into and exit from the
biota is through bacteria.
Some Processes By Which Nutrients
Are Recycled
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Cycling within an
ecosystem involves a
number of processes.
These are best
considered by focusing
attention on specific
nutrients.
CARBON, HYDROGEN AND OXYGEN
CYCLES IN ECOSYSTEMS
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C, H & O basic elements of life; making up from
about 98% of plant biomass.
CO2 and O2 enter biota from the atmosphere.
Producers convert CO2 and H2O into
carbohydrates (CH2O compounds) and release O2
from water.
Producers, consumers and decomposers convert
CH2O compounds, using O2, back into CO2 and
H2O.
CARBON, HYDROGEN AND OXYGEN
CYCLES IN ECOSYSTEMS
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Carbon and oxygen cycle come out of the air as carbon
dioxide during photosynthesis and are returned during
respiration.
Oxygen is produced from water during photosynthesis and
combines with the hydrogen to form water during
respiration.
PHOSPHOROUS CYCLE IN
ECOSYSTEMS
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Phosphorus, as phosphate (PO4-3), is an
essential element of life.
It does not cycle through atmosphere,
thus enters producers through the soil
and is cycled locally through producers,
consumers and decomposers.
Generally, small local losses by leaching
are balanced by gains from the
weathering of rocks.
Over very long time periods
(geological time) phosphorus follows a
sedimentary cycle.
NITROGEN CYCLE IN ECOSYSTEMS
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Nitrogen (N2) makes up 78%
of the atmosphere.
Most living things, however,
can not use atmospheric
nitrogen to make amino-acids
and other nitrogen containing
compounds.
They are dependent on
nitrogen fixing bacteria to
convert N2 into NH3(NH4+).
Sources of Nitrogen to the Soil
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Natural ecosystems
receive their soil nitrogen
through biological fixation
and atmospheric
deposition.
Agricultural ecosystems
receive additional nitrogen
through fertilizer addition.
Biological Sources of Soil Nitrogen
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Only a few species of
bacteria and cyanobacteria
are capable of nitrogen
fixation.
Some are fee-living and
others form mutualistic
associations with plants.
A few are lichens.
Atmospheric Sources of Soil Nitrogen
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Lightning was the major source of
soil nitrogen until recent times
when the burning of fossil fuels
became a major source of
atmospheric deposition.
Nitrogen oxides come from a
variety of combustion sources that
use fossil fuels.
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In urban areas, at least half of these
pollutants come cars and other
vehicles.
Agricultural Supplements to Soil
Nitrogen
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Various forms of commercial
fertilizer are added to
agricultural fields to
supplement the nitrogen lost
through plant harvest.
Crop rotation with legumes
such as soybeans or alfalfa is
also practiced to supplement
soil nitrogen.
Biological Nitrogen Fixation
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Nitrogen fixation is the largest
source of soil nitrogen in natural
ecosystems.
Free-living soil bacteria and
cyanobacteria (blue-green “algae”)
are capable of converting N2 into
ammonia (NH3) and ammonium
(NH4+).
Symbiotic bacteria (Rhizobium) in
the nodules of legumes and certain
other plants can also fix nitrogen.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Nitrification
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Several species of
bacteria can convert
ammonium (NH4+)
into nitrites (NO2-).
Other bacterial species
convert nitrites (NO2-)
to nitrates (NO3-).
Uptake of Nitrogen by Plants
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Plants can take in either ammonium
(NH4+) or nitrates (NO3-) and make
amino acids or nucleic acids.
These molecules are the building blocks
of proteins and DNA, RNA, ATP, NADP,
respectively.
These building blocks of life are passed
on to other trophic levels through
consumption and decomposition.
Ammonification
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Decomposers convert
organic nitrogen (CHON)
into ammonia (NH3) and
ammonium (NH4+).
A large number of species
of bacteria and fungi are
capable of converting
organic molecules into
ammonia.
Denitrification
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A broad range of bacterial
species can convert
nitrites, nitrates and
nitrous oxides into
molecular nitrogen (N2).
They do this under
anaerobic conditions as a
means of obtaining
oxygen (O2).
Thus, the recycling of N is
complete.
NITROGEN CYCLE IN ECOSYSTEMS
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Molecular nitrogen in the air can be
fixed into ammonia by a few species of
prokaryotes.
Other bacterial species convert NH4into NO2- and others to N03-.
Producers can take up NH4- and to
N03- use it to make CHON.
Decomposers use CHON and
produce NH4-.
Recycling is complete when still other
species convert N03- and NO2- into
N2.
NUTRIENT LOSS IN ECOSYSTEMS I
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The role of vegetation in nutrient
cycles is clearly seen in clear cut
experiments at Hubbard Brook.
When all vegetation was cut from a
38-acre watershed, the output of
water and loss of nutrients
increased; 60 fold for nitrates, and
at least 10 fold for other nutrients.
Freeman describes the
experiments on page 1254 and in
Figure 54.15.
NUTRIENT LOSS IN ECOSYSTEMS II
NUTRIENT LOSS IN ECOSYSTEMS III
GLOBAL NUTRIENT CYCLES
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The loss of nutrients from
one ecosystem means a
gain for another.
(Remember the law of
conservation of matter.)
When ecosystems become
linked in this manor,
attention shifts to a global
scale. One is now
considering the
ECOSPHERE or the whole
of planet earth.
GLOBAL WATER CYCLE
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Oceans contain a little less than 98% of the earth’s
water.
Around 1.8% is ice; found in the two polar ice caps
and mountain glaciers.
Only 0.5% is found in the water table and ground
water.
The atmosphere contains only 0.001% of the earth’s
water, but is the major driver of weather.
GLOBAL WATER CYCLE
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The rate at which water cycles
is shown in Figure 54.16
(Freeman, 2005).
Evaporation exceeds
precipitation over the oceans;
thus there is a net movement of
water to the land.
Nearly 60% of the precipitation
that falls on land is either
evaporated or transpired by
plants; the remainder is runoff
and ground water.
GLOBAL WATER CYCLE
GLOBAL CARBON CYCLE
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All but a small portion of the
earth’s carbon (C) is tied up in
sedimentary rocks; but the
portion that circulates is what
sustains life.
The active pool of carbon is
estimated to be around 40,000
gigatons.
Of active carbon, 93.2 % found in
the ocean; 3.7% in soils; 1.7% in
atmosphere; 1.4% in vegetation.
GLOBAL CARBON CYCLE
GLOBAL NITROGEN CYCLE I
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99.4% of exchangeable N is found
in the atmosphere; 0.5% is
dissolved in the ocean; 0.04% in
detritus ; 0.006% as inorganic N
sources; 0.0004% in living biota.
Figure 54.19 in Freeman (2005)
gives major pathways and rates of
exchange.
GLOBAL NITROGEN CYCLE II
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Humans are adding large amounts of N to
ecosystems.
Among the fossil fuel sources, power plants and
automobiles are important sources of
atmospheric nitrogen deposition in the US.
Investigations of native plant and natural
ecosystem responses to nitrogen deposition and
global warming will be a focus of study.
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E.g. invasive species tend to be more devastating to
ecosystems with high soil nitrogen content
GLOBAL NITROGEN CYCLE