Agriculture Reference
In-Depth Information
Table 5.2
Essential Features of the Main Groups Within the Decomposers
Group of
microorganisms
Growth habit
Reproduction
Numbers in the soil
Physiological characteristics
Archaea
Single-cell organisms,
0.1-15 μm in size
Asexual by binary
or multiple
fission
Unknown
No membrane-bound nucleus; both autotrophs and
heterotrophs occur (see table 5.3); first examples found
in extreme environments (hot springs, highly saline,
acidic or alkaline sites)
Bacteria
Single-cell organisms,
0.2-1 μm in size;
favored by moist
conditions
Asexual; rapid
multiplication
by cell division
1-4 billion/g soil;
most species
unidentified
Similar cell structure to Archaea but different cell
biochemistry; heterotrophic and autotrophic nutrition;
some parasites and symbionts; aerobes and anaerobes;
collectively almost limitless variety in metabolism and
ability to use diverse substrates for growth
Fungi
Some are single-celled
(yeasts), but most form
filaments 1-10 μm in
diameter (the hyphae)
that collectively form a
mycelium
Asexually by
cell division
and sexually
by producing
spores on
fruiting bodies
<1 million/g soil;
biomass is larger
than bacteria
Membrane-bound nucleus; heterotrophic; saprophytic
and parasitic; some specialized symbionts as in lichens
and mycorrhizas; more tolerant of soil pH(CaCl
2
)
<5 than most bacteria and many can decompose
recalcitrant C compounds (hemicellulose, lignin, and
chitin)
Actinomycetes
(Actinobacteria)
Grow as networks of fine
hyphae less than 0.5 μm
in diameter; more
delicate than the fungi
Slow growing
No reliable numbers
for soil
Membrane-bound nucleus; heterotrophs; can decompose
hemicellulose, lignin, and chitin; some are pathogens;
some thermophilic types grow in composts at
temperatures >50ºC
Algae
Filamentous or single
celled; grow on land and
in water
Asexual and
sexual
100,000-1 million/g
soil
Membrane-bound nucleus; photosynthetic or
heterotrophic (in the absence of light); Cyanobacteria
or “blue-greens” fix atmospheric N
2
and prefer neutral
to alkaline soils; green algae prefer acid soils
Compiled from Delong (1998), Angle (2000), and Thorn (2000).
