Lecture 9a
Biogeochemical Cycles
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Biogeochemical CyclesCycling of energy, and
various chemical elements
and compounds through the
biosphere due to the
feeding of organisms on
each other
This includes: carbon,
nitrogen, phosphorus,
water...almost anything that
temporarily inhabits a living
thing
Ecosystem Ecology
Food Webs:
The "levels" which organisms eat which one's
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"lower" on the chain"—
are called TROPHIC LEVELS
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(from the Greek troph, meaning "food" or "nourishment")
The Food Web reflects the flow of ENERGY
and NUTRIENTS through ecosystems via
the trophic levels.
The efficiency with which trophic levels
convert energy from the previous trophic
levels varies greatly with ecosystem, but
usually ranges between 5% - 20%.
Organisms in the food web
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Autotrophs: Organisms that can
feed themselves by harnessing light
energy to make organic molecules
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carbohydrates, proteins, lipids, and
nucleic acids out of inorganic raw
materials (such as carbon dioxide,
water, nitrogen compounds, etc.)
Autotrophs = Primary Producers,
because they are the first link in
the food web/chain. Without their
ability to capture light and
"harness" it as solid, organic
matter, life as we know it would
not exist.
Heterotrophs: Organisms that feed on
other organisms to obtain energy.
+
=
Carbon
Cycle
All organic matter
(carbon
compounds) on the
earths surface is
eventually
oxidized (burned)
and changed to
carbon dioxide and
water.
C6H12O6
Photosynthesis
Soil Food Web
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The community of
organisms living all or
part of their lives in the
soil
Fueled by primary
producers
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plants, lichens,
moss,
photosynthetic
bacteria, and algae
http://www.agron.iastate.ed
u/~loynachan/mov/
Or foodchain.rm
Photosynthesizers
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Plants
Algae
Bacteria
Role:
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Capture solar energy to fix CO2
Add organic matter to soil (biomass such as
dead cells, plant litter)
Decomposers
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Bacteria
Fungi
Protozoa
Role:
 Breakdown residue
 Immobilize nutrients
their biomass
 Create new organic compounds
 Bind soil aggregates
in
Mutualists
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Two organisms living in beneficial association
Bacteria
Fungi
Role:
 Enhance plant growth
 Fix nitrogen
Pathogens/Parasites
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Bacteria
Fungi
Nematodes
Role:
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Promote disease
Consume roots
Parasitize nematodes
or insects
Root-feeders
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Nematodes
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Role:
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Consume plant roots
Crop yield losses
Shredders
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Earthworms
Arthropods (millipedes)
Role:
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Breakdown residue
Enhance soil structure
Provide habitat
bacteria in gut
Most millipedes eat decaying
leaves & dead plant matter,
Measurement of Microbial Activity
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Counting
 Direct counts
 Plate counts
Activity levels
 Respiration
 Nitrification
rates
 Decomposition
rates
Cellular
constituents
 Biomass C, N, or P
 DNA/RNA
fingerprinting
Ratio of Fungi to Bacteria
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Disturbed have a strong
bacterial dominance.
Non-disturbed, fungi start
to move in until habitats
like prairies or your lawn
have a relatively even
proportion of fungi and
bacteria in residence.
If shrubs and trees take
over, the fungi in the soil
build up and are strongly
fungi dominated.
http://www.waldeneffect.org/blog/Fungi_to_bacteria_ratio/
.
Soil management affects the fungal and bacterial populations in soil
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Fungi and bacteria differ in their responses to
changes in agricultural practices.
Fungi are usually more sensitive to these
changes. The fungal-to-bacterial ratio is
therefore an indicator of environmental changes
in the soil.
When plant residues are surface applied - fungi
prosper because their hyphae are able to grow
into the litter layer.
Tillage - destroys large amounts of the fungal
hyphae.
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Incorporation of plant residues into the soil favors
the bacterial population because the contact
surface between the substrate and bacteria is
increased.
Fungi are the predominant cellulose
decomposers. Bacteria, which have a smaller C:N
ratio than fungi, need food rich in nitrogen (e.g.
green manure, legume residues).
A high nitrogen fertilizer favors the bacterial
community in a soil
Substrate additions with a relatively wide C:N
ratio enables growth of the fungal population.
Garden Plants
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carrots, lettuce, and
crucifers enjoy strongly
bacteria dominated soils
tomatoes & corn like
soils that are closer to
1:1 (though still leaning
a bit toward bacteria)
perennials, shrubs, and
trees like the soil to be
full of fungi at ratios from
10:1 to 50:1.
Soil Biota
only 1 to 5% of all biota on Earth have been named and classified.
many unknown species are thought to reside in the soil.
possible number of existing species of different groups are
staggering:
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1.5 million species of fungi,
300,000 species of bacteria,
400,000 species of nematodes
40,000 species of protozoa
Soil has potential for commercial exploitation in biotechnology, in
areas such as medicine, industrial processes, agriculture and
bioremediation of polluted wastes, waters and land.
Most clinically relevant antibiotics today originate from soildwelling actinomycetes and the potential uses of other biota and
their products are being actively pursued.
For example, enediynes are a natural toxin produced by soil
bacteria which have been found to be one the most effective
known anticancer agents
Rates of Plant Residue Decomposition
Kind of material
(FAST --> Sugar, starches, proteins --> SLOWER hemicelluloses, cellulose, -->
SLOWEST Fats waxes --> lignin
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Rate decreases after the easy
material has decomposed
Soil Conditions - water, temp.,
oxygen, nitrogen, phosphorus,
Decay Products = Energy
(heat), carbon dioxide, N,P,S &
Humus
Carbon Dioxide & Global Warming
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The use of fossil fuels and
practice of deforestation to
meet the world's energy
demands has lead to increasing
concentrations of carbon
dioxide (CO2) and methane
(CH4) in the atmosphere.
Both gases absorb terrestrial
infrared radiation and have
the potential to affect earth's
climate by warming it.
Sources of Atmospheric Carbon
Atmospheric carbon
represented a steady state
system, where influx equaled
outflow, before the
Industrial Revolution.
Currently, it is no longer a
steady state system because
the influx exceeds the
outflow.
Therefore, we are experiencing
an increase in atmospheric
carbon, mainly in the form of
CO2
Dennis L. Hartmann
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The characteristics of
the atmosphere that
enable it to raise the
temperature of the
surface of Earth are:
1) atmosphere is
transparent to sunshine
2) but is almost opaque
to infrared radiation.
So the atmosphere lets
in the heat from the sun,
but is reluctant to let it
escape again due to the
“greenhouse gasses”
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If CO2 is suddenly
added to the
atmosphere, it takes
between 50 and 200
years for the amount
of atmospheric CO2 to
establish a new
balance, compared to
several weeks required
for water vapor.
DYAD
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What are you going to do about “Climate
Change”?
Soil Carbon Sinks
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Large amounts of carbon have
been released into the
atmosphere through the
conversion of grasslands and
forests to agricultural and
grazing land, as well as
through unsustainable land
practices.
Soils can regain lost carbon by
absorbing or "sequestering" it
from the atmosphere. But the
ability of soils to act as
carbon "sinks“ depends on
sound land management.
Holding carbon in the soil!
Soil Carbon “C”
: easy come, easy go!
Deep plowing of organic
matter might increase
Carbon storage for the
upper foot of soil.
Gaining Carbon
Conservation tillage and cover crops
may result in net carbon sequestration.
Losing Carbon
Intensive tillage results in carbon loss.
Fossil carbon cycle.
Biological carbon cycle.
Atmospheric Carbon as CO2
CO2
Energy from
fossil fuels
CO2
Energy from
bio-fuels
CO2
C
Plant biomass and
roots left on or in
the soil contribute
to Soil Carbon or
Soil Organic Matter
and all associated
environmental and
production
benefits.
Nonrenewable
Renewable
Soil is meant to be covered.
Manage soil carbon - make the world a better place.
D.C. Reicosky USDA - ARS -Morris Lab