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.)
