Lecture 9aBiogeochemical Cycles

Biogeochemical Cycles- Cycling 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 "lower" on the chain"— are called TROPHIC LEVELS

(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 Autotrophs: Organisms that can

feed themselves by harnessing light energy to make organic molecules 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 The community of

organisms living all or part of their lives in the soil

Fueled by primary producers plants, lichens,

moss, photosynthetic bacteria, and algae

http://www.agron.iastate.edu/~loynachan/mov/

Or foodchain.rm

Photosynthesizers

Plants Algae Bacteria Role:

Capture solar energy to fix CO2

Add organic matter to soil (biomass such as dead cells, plant litter)

Decomposers

Bacteria Fungi Protozoa Role:

Breakdown residue Immobilize nutrients in

their biomass Create new organic compounds Bind soil aggregates

Mutualists Two organisms living in beneficial association Bacteria Fungi Role:

Enhance plant growth Fix nitrogen

Pathogens/Parasites

Bacteria Fungi Nematodes Role:

Promote disease Consume roots Parasitize nematodes

or insects

Root-feeders

Nematodes

Role: Consume plant roots Crop yield losses

Shredders

Earthworms Arthropods (millipedes)

Role: Breakdown residue Enhance soil structure Provide habitat

bacteria in gut

Most millipedes eat decaying leaves & dead plant matter,

Measurement of Microbial Activity

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

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/

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Soil management affects the fungal and bacterial populations in soil 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. 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

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: 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 soil-dwelling 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

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

Kind of material (FAST --> Sugar, starches, proteins --> SLOWER hemicelluloses, cellulose, --> SLOWEST Fats waxes --> lignin

Carbon Dioxide & Global Warming 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

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”

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

What are you going to do about “Climate Change”?

Soil Carbon Sinks 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!

Gaining Carbon Losing Carbon

Conservation tillage and cover crops may result in net carbon sequestration.

Soil Carbon “C” : easy come, easy go!

Intensive tillage results in carbon loss.

Deep plowing of organic matter might increaseCarbon storage for the upper foot of soil.

Atmospheric Carbon as CO2

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.

Energy from bio-fuels

CO2 CO2

Biological carbon cycle.Fossil carbon cycle.

CO2

CEnergy from fossil fuels

RenewableNonrenewable

Soil is meant to be covered.

Manage soil carbon - make the world a better place.

D.C. Reicosky USDA - ARS -Morris Lab