Soil Biology - Soil Organisms

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Importance of soil biology:
• Decomposition / SOM transformations
• Conversion of nutrients from organic to inorganic (plant available forms)
• Release of nutrients
• C cycling
• N cycling
• Soil structure (burrowing, mixing, fecal pellets, cementing agents)
classification of soil organisms is based on:
1. size
2. function
heterotrophs
use organic compounds as a source of E and C
autotrophs
C from CO2 and E from photosynthesis/oxidation of various elements/compounds
algae
have chlorophyll and perform photosynthesis; live at or close to the soil surface
types of algae
1. green algae
2. diatoms
3. yellow-green algae
fungi
are heterotropic (mainly) aerobic organisms; responsible for much of organic
matter decomposition in most soils
types of fungi
1. yeast
2. molds
3. mushroom fungi
bacteria
the most diverse and abundant
group of soil organisms; organic matter decomposers; some are capable of fixing atmospheric N
actinomycetes
are "filamentous bacteria" that decompose soil organic matter; some produce antibiotics
cyanobacteria (aka blue-green algae)
• Have chlorophyll and perform photosynthesis
• Some can fix atmospheric N (Anabaenasp.)
• Some are symbionts with lichens,protozoa, diatoms, algae
vertebrates
(mice, moles, ground squirrels, etc.) mix soil through their burrowing activity
annelids (segmented worms)
most important representatives are earthworms
Arthropods (spiders, mites, springtails, insects)
shred plant residues, mix it with soil, and stimulate decomposition within their intestines
protozoa
are "primitive animals" that feed on bacteria, fungi, or fragments of organic matter
nematodes (thread worms)
after consuming bacteria, nematodes excrete much of the excess N as inorganic N (ammonia), hence increasing mineralization
Micro-organism are most numerous in soils with:
1.field capacity moisture
2. temp near 30C
3. near pH7
4. high nutrient content
essential nutrients
C, H, O, H, P, K, Ca, Mg, S, Fe, Mn, Zn and Cu
Biochemical reactions
such as OM decomposition are mediated by enzymes
enzymes
are products of soil organisms
biochemical reactions in well aerated soils
release various important nutrients
biochemical reactions in poorly aerated soils
release less desirable products
Respiration and fermentation
carried out by heterotrophic organisms that obtain energy from the oxidation of OM
oxidation-reduction
all biochemical reactions of C, N, and S
OIL RIG
Oxidation Is Loss (of electron)
Reduction Is Gain (of electron)
Rhizosphere
Narrow region of soil directly influenced by root secretions and associated soil micro-organisms
- sloughed off plant cells, roots secretions (enzymes, proteins, sugars)
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