SOIL - CHAPTER 4

Soil Organism

Creatures that spend all of their lives in the soil environment

Macrofauna

moles, mice, ants,beetles,termites,grubs,millipedes and earthworms

Mesofauna

springtails and mites

Microfauna

nematodes and single celled protozoans

Flora

plant roots, algae and diatoms

Microorganism

fungi, bacteria and actinomycetes

Species Diversity

the mix of species present

Functional Diversity

the capacity to use a wide variety of substrate and provide a range of ecosystem services.

Functional Redundancy

several organisms can carry out each ecosystem service: Leads to ecosystem stability and resilience

Keystone species

a species that is unique in filling an ecological niche and is therefore integral to the functioning of that system

Global Biodiversity

great genetic resource of soil organisms

Stability

the ability of soil, even in the face of wide variations in the environmental conditions and inputs, to continue to perform such functions of: cycling of nutrients; assimilation of organic waste; maintenance of soil structure.

Resilience

the ability of soil to bounce back to functional health after severe disturbance has disrupted normal processes

Soil Food Web

The community of organism living all/part of their lives in the soil

Autotrophs

organism that can feed themselves by harnessing light energy to make organic molecules such as carbohydrates; proteins, lipid and nucleic acid out of inorganic raw materials

Heterotrophs

organism capable of deriving energy for the life processes only from decomposition of organic compound and incapable of using inorganic compound such as sole sources of energy

Photosynthesizers

First trophic level - algae Ø Role: capture solar energy to fix carbon dioxide

Decomposers

Second trophic level - bacteria, fungi, protozoa Ø Role: breakdown residue, immobilizes nutrient in their biomass, create new organic compound, bind soil aggregates

Mutualist

Second trophic level; Two organisms living in beneficial association -bacteria, fungi- Ø Role: enhance plant growth, fix N

Symbiosis with mycorrhiza

Facilitates the uptake of P, other nutrients and water uptake Ø Glomus spp. P.tinctorious etc

Biological Nitrogen Fixation (BNF)

Process by which microorganism in the soil fix atmospheric N and make it available for assimilation by plants. Ø Rhizobium, Azospirillum etc.

Pathogen/Parasites

Second trophic level - bacteria, fungi, nematode, arthropods Ø Role: promote diseases, consume roots

Root- feeders

Second trophic level - nematodes, arthropods Ø Role: consume plant roots, crop yield loss

Shredders

Third trophic level - earthworm, arthropods Ø Role: breakdown residue, enhance soil structure and provide habitat for bacteria in gut

Organism abundance

Soil organism number are influenced primarily by amount and quality of food available and management practices

physical factor

moisture temperature

biotic factor

predation and competition

chemical characteristics of soil

acidity, alkalinity and salinity

Earthworm

Digest organic and mineral matter passing their bodies-30t/ha/year

Earthworm

Excrete cast that has high amount of nutrients;

Earthworm

Facilitate aeration and drainage- through channels created

Earthworm

Increase size and stability of soil aggregates

Nematodes

Help decomposition of OM -they invade plant roots and cause the death of roots

Protozoa

They ingest other soil organism particularly bacteria -help hasten the release of some nutrient that have been immobilized by bacteria

Bacteria

Involved in OM decomposition as well as in various transformation of nutrients such as: ammonification, nitrification, denitrification, immobilization, biological N fixation etc.

Fungi

The most adaptable and versatile of soil organism

Fungi

Able to thrive in extreme acidity and alkalinity

Fungi

Able to decompose even the resistant organic compound such as lignin,cellulose.

Mycorrhizae

help plants in solubilization of P an its absorption

Actinomycetes

These organisms also attack and simplify complex and resistant organic compound such as cellulose, chitin and phospholipids

Autotrophic

use carbon dioxide as their source of C and derived energy for their metabolism from the oxidation of simple inorganic compound

Heterotrophic

oxidize organic matter to get C and energy

Chemoautotrophic

use inorganic chemical compound

Photoautotrophic

use sunlight as their source of energy

Aerobic

requires oxygen to survive

Anaerobic

not requires oxygen to survive

Facultative

organism that makes ATP by aerobic respiration if oxygen is present but capable of switching to fermentation

Microaerophiles

need low concentration of oxygen

Aerotolerant

does not need oxygen but is not poisoned by oxygen

Mesophilic

(20-45 0C)

Thermophilic

(45- 80 0C)

Psychrophillic or cryophilic

( -20 -10 0C)

Hyperthermophilic

(\> 115 0C)

Acidophiles

grow best in acidic condition

Neutrophiles

grow best at neutral pH

Alkaliphiles

grow best in alkaline condition

Halophiles

requires some NaCl for growth

Mild

requires 1-6% salt

Moderate

requires 6-15% salt

Extreme

requires 15-30% salt

Halotolerant

grow best in the absence of NaCl

Osmophiles

organisms able to live in environment high in sugar

Xerophiles

organisms which live in dry environment

Carbon Cycle

All organic matter eventually is oxidized (burned) and convert back to carbon dioxide and water

Decomposition of Organic Compounds in Aerobic Soils

1. Carbon compound are enzymatically oxidized to produce CO2, H2O, energy and decomposer biomass.

Decomposition of Organic Compounds in Aerobic Soils

2. The essential nutrient element such as: N, P and S are release and/or immobilized by series of specific reaction that are relatively unique each element.

Decomposition of Organic Compounds in Aerobic Soils

3. Compound resistant to microbial action are formed, either: through modification of compounds in the original tissue or by microbial synthesis

Decomposition in Anaerobic Soils

The product of anaerobic decomposition include a wide variety o partially oxidized organic compound such as: organic acids, alcohols, methane gas.

Decomposition in Anaerobic Soils

Anaerobic decomposition releases relatively little energy for organism involved.

Decomposition in Anaerobic Soils

Issues related to the product of anaerobic decomposition; they produce foul odor/ inhibit plant growth; the methane gas produce in wet soils is a major contributor to greenhouse effect

Nitrogen Cycle

Form of N in the soil

Organic N

amino acid

Organic N

amino sugar

Inorganic N

NH4+(ammonium)

Inorganic N

N2O (nitrous oxide)

Inorganic N

NO3-(nitrate) N

Inorganic N

O2 (nitrogen dioxide)

Inorganic N

NO2-(nitrite)

Inorganic N

NO (nitric oxide)

Inorganic N

N2(nitrogen gas)

Inorganic N

NH3 (ammonia)

Mineralization

conversion of organic N into inorganic forms

Immobilization

the conversion of inorganic N back to organic N; Available N is used by soil microorganism and assimilated into their bodies

Biological Nitrogen Fixation

Conversion/ reduction of nitrogen gas into ammonia

Biological Nitrogen Fixation

Can only be done biologically by high specialized group of micro organism in the presence of the enzyme nitrogenase which catalyzes the reduction of nitrogen gas into ammonia

Biological Nitrogen Fixation

N2 + 6e-+ 8H+ 2NH3 + H2

Symbiotic Nitrogen Fixation

Association between higher plant (macrosymbiont) and a microorganism (microsymbiont) to acquire N from atmosphere Example: Rhizobium

Symbiotic Nitrogen Fixation

The irritation causes nodules to form in roots. The bacteria in the roots trap atmospheric N which transform into NH3. NH3 combines with organic compound to form amino acids and proteins. In turn, the plant supplies the carbohydrates and energy for their metabolism.

Non- Symbiotic Nitrogen Fixation

Conversion of atmospheric N by microorganism without associated plant host

Nitrification

Biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of nitrite to nitrate

Denitrification

Biochemical reduction of nitrate to gaseous N by anaerobic soil organism

Ammonification

Result of the breakdown of organic matter such as dead animals and plants or waste material like excrement

Ammonification

Microorganism produce ammonia and related compounds as a by-product of their metabolisms

Sulfur Cycle

Like N, sulfur also undergoes mineralization, immobilization, oxidation-reduction through microbial activities.

Sulfur Cycle

S become available to plant through decomposition of S- containing compound like: cysteine and methionine.

Sulfur Cycle

Under aerobic environment, S may be oxidized by Thiobacillus thioxidans to SO42-with release of energy.

Sulfur Cycle

Under anaerobic conditions as in paddy soils, sulfate may be reduced by the bacteria Desulfovibrio desulfuricans.

Sulfur Cycle

They use the oxygen in sulfate to oxidize organic compound; The end product is H2S; The characteristic offensive odor of flooded soils is primarily emanating from H2S

Pesticide Degradation

Biochemical degradation by soil organisms is the single most important method by which pesticide are removed from the soil.

Pesticide Degradation

Certain polar groups on the pesticide molecules, such as –OH, -COO and NH2 provide points of the attack for the organisms