2 - Chapter 30 - Microorganisms in Terrestrial Ecosystems

Where is microbial diversity greater

in soil compared to aquatic environments

how much of soil function is mediated by microbes

90%

level of microbial diversity is supported by what

by complex physical and chemical environments (soil particles, pore space)

what is pore space important for

critical for movement of water and gases, optimum environment for microbial growth

Categories of soil constituents (living organisms)

Plant root system, worms, insects, rodents, microbes

what are the categories of soil

mineral and organic soil

describe mineral soil

contains less than 20% organic carbon, most soils in this category

describe organic soil

contains at least 20% organic carbon

how are mineral particles formed

weathering of rock, degradative metabolic activities of microbes

what elements are in mineral particles

mostly silicon, aluminum, iron. some calcium, magnesium, potassium, titanium, manganese, sodium, nitrogen, phosphorus, and sulfur

how is organic material formed

plant and animal wastes and remains

what is humus

what is left after the last decomposition stage, can’t degrade further

when does humus result

when plant material has been incompletely degraded by microbes

what is humus a blend of

complex blend of phenolic compounds, polysaccharides, and proteins

what does humus do once formed

integrates the permanent structure of soil, contributes to its improvement

what does humus allow for

soil organisms to feed and reproduce, often described as the “life force”

what kind of bacteria make up organic matter?

both dead and living

SOM

soil organic matter

importance of soil organic matter

retains nutrients, maintains soil structure, holds water for plant use, levels change depending on environmental conditions and agricultural management practices

categories of soil constituents

water and gases

water as a soil constituent is dependent on?

precipitation, climate, drainage, living organisms present

adsorbed onto soil particles

water

what might water contain as nutrients?

dissolved organic and inorganic components

what gases are present (gas as a soil constituent)

CO2, O2, N2

where is gas in the soil found

in the spaces between the soil particles where there is no moisture

where is some extra CO2 found

dissolved in water

what is the inverse relationship of gas and water?

Amount of gas is inversely related to the amount of moisture present

what is microbial content of soil influenced by

amount and type of nutrition, available moisture, degree of aeration, temperature, pH, agriculture practices, local environment (floods, tornadoes), climate variations, microbial community (relationships)

degradation of plant material and SOM depends on:

release of CO2 and biomass production, small fraction becomes SOM

Production of SOM: easily degraded compounds like carbohydrates and proteins are broken down

½ becomes CO2 and rest is incorporated as biomass

Production of SOM: complex carbohydrates like cellulose are degraded

fungi and bacteria produce cellulase

Production of SOM: resistant material like lignin is degraded by fungi

lignin (irregular branched carbohydrate) is formed from polymers of phenylpropene units

what is lignin degradation slower than

cellulose degradation

what oxygen conditions does most lignin degradation occur under?

majority is aerobic

how does lignin degrade under anaerobic condition

very slowy

how are peat bogs and muck soils formed

ligning degradation accumulates

what percentage is converted to biomass under lignin degredation?

no more than 10%

practical importance of lignin degradation

preservation of wood pilings below the water table

what factors is degradation of organic matter influenced by

nutrients present in environment, abiotic conditions, microbial community present

what is mineralization

decomposition of organic matter to simpler inorganic compounds

what is nutrient immobilization

the nutrients that are converted into biomass become temporarily unavailable for nutrient cycling

oxic conditions

oxidized accumulate (nitrate, sulfate, CO2)

anoxic condition

reduced accumulate (ammonium, sulfide, methane)

carbon enters common pool of organic matter that can be…

oxidized back to CO2

oxidized example

CO and CO2

what does the carbon cycle begin with

carbon fixation

how much carbon is fixed aerobically vs anaerobically?

at least half of carbon on earth is fixed aerobically and anaerobically (CO2 into organic matter) by microbes

how is inorganic and organic carbon reduced anaerobically to methane

by archaea

what are the most important sources of methane

rice paddies, ruminant animals, coal mines, sewage treatment plants, landfills, marshes

what ration is nitrogen level in soil typically considered in

carbon to nitrogen ratio C/N

what C/N ratio allows for maximal decomposition

30, allows microbe to convert ammonium and nitrate to biomass

what does a C/N of 30 or less result in

loss of soluble nitrogen from the system

what is a C/N above 30 considered?

nitrogen limited

what factors affect nitrogen levels in soil

agricultural fertilizers, fossil fuel combustion, occult nitrogen accretion (nitrogen from atmospheric sources)

what is the nitrogen saturation point

point beyond any nitrogen added to soil will not be incorporated into organic matter and remain in mobile form

when is the soil said to reach the nitrogen saturation point

when addition of nitrogen under low C/N does not stimulate growth

what reaction is nitrogen fixation

reduction of N2 to organic nitrogen

what origin is all naturally produced organic nitrogen from?

prokaryotic

nitrogen fixation is carried out by microbes with what oxygen requirements

aerobes or anaerobes

microbes present in all 5 major nutritional types

autotrophs, photoautotroph, chemautotroph, heterotroph, photoheterotrophs, chemoheterotrophs

what nitrogen cycling reactions are only performed by microbes

NH3 to NO2,

NO2 to NO3,

NO3 to N2,

N2 to NH3

N2

nitrogen

NH3

ammonia

NH4+

ammonium

NO2-

nitrite

NO3-

nitrate

N2O

nitrous oxide

NO and NO2 in atmospheric fixation

nitric oxide and nitrogen dioxide

what is the product of nitrogen fixation

ammonia

how is ammonia immediately incorporated into organic matter

as an amine (proteins, nucleic acids, biomolecules)

what shuttles amino acids with newly fixed nitrogen to the plant

bacteroids

when is organic N converted to NH4+

during decay and mineralization of organic matter

what does mineralization require

an assemblage of microbes

what is nitrification

deamination of amino acids

what type of process is nitrification

2 step chemolithotrophic process (NH4+ to NO2- to NO3-)

nitrate reduction

nitrate can be reduced and incorporated into cell biomass

what are the types of nitrate reduction

assimilatory nitrate reduction, dissimilatory nitrate reduction, denitrification

assimilatory nitrate reduction

NO3- is reduced and incorporated into organic nitrogen (amino acids, proteins, nucleic acids)

Some reduction to NO2- in anaerobic conditions (not assimilated into biomass)

delete

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denitrification (NO3- to N2 and N2O)

NO3- removed from ecosystem and returned to atmosphere as dintrogen gas or nitrous oxide; possible nitrite

what forms are referred to as Nox

NO and N2O

global warming potential of Nox

280x that of CO2

how does fertilizer manufacturing reduce N2 to NH4+

uses hydrogen gas

what happens to extra NH4+ not taken up by plants

runoff can cause eutrophication

nitrification/denitrification cycles fueled by fertilizer are responsible for high Nox levels

how much percentage of fixation process is lightning responsible for

5-8%

what is the anammox process

anaerobic ammonium oxidation

anaerobic oxidation of NH4+ (electron donor) using NO2- as the electron acceptor

what does the anammox process result in

production of nitrogen gas (N2)

NH4+ + NO2- to N2 (chemolithotrophy)

shortcut to production of nitrogen gas without having to cycle through nitrate

anammox process

what is the limiting element in most freshwater systems

phosphorous

phosphorus binding to soil is dependent on what?

cation exchange capacity (CEC) and soil pH

what is cation exchange capacity (CEC)

sum total of exchangeable cations that a soil can adsorb

a fundamental life supporting process

cation exchange with photosynthesis

excessive amounts of phosphorous can contribute to what?

eutrophication of water sources

Penicillium bilaiae is a species of native soil fungus that can be used as a?

plant growth promoting microorganism (PGPM)

organic acids excreted by the microorganism can..

solubilize soil bound phosphate

how can Penicillium bilaiae live in symbiosis with plant species

enhances phosphate uptake by the root structure while feeding off plant waste products (metabolites)

how can soil phosphorous be increased?

agricultural inoculant

bacteria and archaea in forest soil and grassland soil

f: 4 × 10^7 per gram

g: 2 × 10^9 per gram

1 gram of soil is more diverse than

~ 16,000 unknown species

how many microbes per gram of soil

billions