10. Soil Ecology Flashcards
Global distribution of soil animal species is influenced by ….(2)
Forest: low pH + high C:N =
Grasslands: high pH + low C:N=
soil pH and the ratio of C to N in the soil
anthropods»>
nematodes»>
Tremendous diversity is possible because of the nearly limitless variety of … and the wide range of … found in soils
The populations of soil organisms tend to be concentrated in zones of favorable conditions, rather than …
foods
habitat conditions
evenly distributed throughout the soil.
The …can be considered a fundamental unit of habitat for meso- and microorganisms, providing a complex range of …
soil aggregate
hiding places, food sources, environmental gradients, and genetic isolation on a microscale.
Biological diversity is an indicator of …
soil health
–> almost every phylum represented in soil
The mesofauna and macrofauna enhance the activity of the microbes in several ways.: (3)
First, their chewing action fragments the litter, cutting through the resistant waxy coatings on many leaves to expose the more easily decomposed cell contents for microbial digestion.
Second, the chewed plant tissues are thoroughly mixed with microorganisms in the animal gut, where conditions are ideal for microbial activity.
Third, the mobile animals carry microorganisms with them and help the latter to disperse and find new food sources to decompose.
Earthworms present something of a soil conundrum because the same activities that promote organic matter incorporation and nutrient cycling and aid plant growth also promote increased emissions of carbon dioxide and nitrous oxide, two major gases that drive global warming .
earthworm incorporation of plant litter substantially increased plant uptake of nitrogen, but also stimulated the loss of nitrogen as nitrous oxide gas.
The zone of greatest microbial activity usually occurs ….
just a few cm below the soil surface where oxygen is high and the soil is not too dry
organism abundance is controlled by the
supply of decomposable o.m. (food supply)
functional diversity:
competition
resilience
stability
want diversity in both species and functions
greater abundance of organisms:
closer to surface
= greater activity closer to surface
–> algae confined to surface (need light)
Fungi, bacteria, roots = deeper
Nematodes
Most abundant animal on earth: 4 of every 5 animals
➢ Free living worms, parasitic worms, worms that eat
decaying tissue, roundworm eating roundworms, etc.
➢ Range in size from micro-metres to metres (placental
parasite in sperm whales)
➢ 25,000 named species, but total estimated at about 1
million
➢ Most abundant in marine sediments, then in soils.
➢ Specialist parasites in half of all animals
➢ Researched: parasites and root infection agents
Earthworms
Most important macro-faunal component of soils
- Ingest soil & detritus, feeding on bacteria &
fungi in these materials - Improve physical conditions – macropores
- Increase availability of nutrients - casts (= more fertile)
*Enhanced by o.m., lime, good drainage (aeration) - Discouraged by: Tillage, very sandy, v. acid condition
Termites
Social insects, comparable biomass to earthworms most common in drier tropics conditions
not as beneficial as earthworms
produce methane (CH4) from bacteria in gut
build-up nutrient rich mounds
more and rework large amounts of soil material and incorporate large amounts of o.m.
Ants
nearly 9000 species of soil dwelling ants
collect plant material: detrivores and herbivores
can farm aphids (protecting aphid on plants, symbiotic relationships with ants-aphid)
microanimals (2 most important ones)
- nematodes
tiny, unsegmented roundworms
numerous feeding niches
root attacks-agriculture problems - Protozoa
mobile, single cell
most varied and numerous soil fauna
amoeba, ciliates, flagellata
responsible for numerous water-borne diseases
Both predation on fungi + bacteria
–> helps accelerate nutrient cycling (speed IP b.d. of o.m.)
algae
single cell
photosynthesizing (restricted close to surface)
aid soil aggregation + stability
plant roots
feeder roots and root hairs often considered to be soil organisms (die, live in soil, source of food)
add o.m. exudates
support microbial activity
rhizosphere (immediate vicinity of roots) = greater abundance of microbes (than soil body)
–>get substances from root exudates)
soil fungi
Includes single cell yeasts that live in anaerobic
conditions.
Most are filamentous; masses of hyphae =mycelia, and fruit are mushrooms
–> hyphae= networks of filaments colonizing soil
- More important than bacteria in producing humus & stabilizing soil aggregates
- Some control pathogens, some are pathogenic on
higher plants - Some are symbiotic mycorrhizae on plant roots
– Assist plants in obtaining nutrients (in return for energy
supply – sugars)
fairy rings
dark green growth of grass, caused by the advancing hyphal front releasing nutrients and stimulating the growth of the grass. Inside this is usually a zone of poor grass growth caused by the available nutrients being taken up by the fungus. Further towards the centre of the ring the grass growth becomes better again as the old hyphae die and nutrients are released
naturally occurring ring or arc of mushrooms. They are found mainly in forested areas, but also appear in grasslands and/or rangelands
2 types mycorrhizae
- Endo (arbuscular)
inside cell wall
most abundant type - ecto
outside, external to cell wall (in between them)
–> increase scavenging area for nutrients
Actinomycetes
cell size and structure similar to bacteria
mostly aerobic heterotrophs, break down o.m.
important for decomposition + composting
Bacterias
more diverse
many aerobic heterotrophs
some autotrophs (fixing N + S supplies)
–> with cyanobacteria = responsible for much of the N fixing on earth
symbiotic root associations
Rhizobacteria: nodules on legume roots that can capture atmospheric N + fix it
Mycorrhizal fungi: connects plants (assist nutrient uptake + transfer), makes exchange possible by making root systems interact
Legume: receives N from rhizobacteria so it can make amino acids/proteins. transfers N to non-legume. Receives P from non-legume
Nonlegume: receives N from legume, transfers P to legumes
Ecological interactions
Competition between various organisms is keen –
production of iron-binding siderophores and antibiotics (to disadvantage competitors)
- Some soil mgmt practices might inhibit soil organisms
– tillage is mostly negative - Some pesticides (e.g. fumigants) are detrimental, but
others are neutral or a food source - O.M. is beneficial to populations & diversity
- Maintain healthy diversity is probably beneficial in that a full system of competitors is present
Insecticide effect on litter break down is indirect:
through loss of control of nematode bacterivores
affects break down rates
affects representation of organisms in soil
Mgmt decreasing biodiversity and populations
fumigants
nematicides
some insecticides
compaction
soil erosion
heavy metals, industrial wastes
monocropping
extensive tillage
plastic mulches
Mgmt increasing biodiversity and populations
balanced fertilizer use
lime on acid soils
proper irigation
improved drainage, aeration
animal manures, compost
sewage sludge
crop rotations
reduced, or zero tillage
cover crops
grass-legume pastures
residues returned to soil surface
organic mulches
Energy supply is largely the …. also need nutrients; competition for nutrients
pool of organic matter;
Vital processing plant; … (3) assisted with symbiotic forms
produce humus;
re-cycle carbon and mineral nutrients, in plant-available inorganic forms;
mediate redox reactions
