This is a nice summary of the soil science subject. It is partly based upon the book "essential soil science; a clear and concise introduction to soil science" by M.R. Ashman and G. Puri and also of the lectures and powerpoints given at Avans hogeschool.
Soil microbes and nutrient cycles
We divide microbes in the soil into three groups: Microbiota (bacteria, protozoa, fungi, algae),
mesobiota(nematodes, rotifers, springtails, mites) and macrobiota(earthworm, slugs, snail, insects).
Microbiota
This group is <2mm in size.
Bacteria:
Unicellular, prokaryotic (no organelles and all DNA are in the cytoplasm, some have primitive
forms for organelles)
Often found around the plant roots, because there is a lot of nutrients and oxygen
Often anchored to soil particles (gum or electromagnetically)
Morphology: rod-, round-, or line-shaped
Gram-positive and gram-negative bacteria. This is determined by the thickness and chemical
combination of the cell wall.
Some photosynthesize using CO2 and water from the air to make hydrocarbon, others bind
nitrogen from the atmosphere, they are called N-fixers.
Fungi:
Highest biomass of all the soil organisms.
They are eukaryotic
They produce strings of cells called hyphae, which creates a network of hyphae-treads called
mycelia.
A big part of the soil is decomposed fungi.
To survive harsh conditions they can:
o Increase the thickness of their cell wall, called chlamydospores.
o Or forming a structure called sclerotium. A hardened mass containing food.
Fungi like acid conditions
Well-known for breakdown of woody tissue.
Algae:
Algae are single-celled organisms that are found single, in colonies or as filament strands.
They live mainly in aquatic environment, and often found in the top layers of the soil.
They are photosynthetic and can play an important role in primary colonization.
Protozoa:
Bacterial grazers (eat bacteria for food).
Reliant on moisture and thus mostly present in the water film surrounding the soil particles.
Can survive harsh conditions by forming cysts, which suspend the activity until conditions
improve.
Mesobiota
Mesobiota consist of nematodes, rotifers, springtails, mites and some other types.
Nematodes:
Are the most important soil organisms that help with the nutrient recycling.
The nematodes are mostly aquatic and between 0,5 and 1,5 mm.
Macrobiota
These are organisms larger than 1 cm, including earthworm, slugs, snail, insects.
Earthworm:
Is the most important macrobiota to recycle nutrients in the soil because they break down
organic matter to smaller pieces and increasing the surface area and speeding up the
decomposition by bacteria and fungi.
They are also so called grazers, they eat smaller organisms that are in the soil.
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