Soil Biology Flashcards
What is a soil food web?
a community made up of the complex diversity of organisms that spend all or part of their lives in the soil or consume organisms that live in the soil
What does the diagram of the food web show us?
The transfer of energy between trophic levels
6 roles of organisms in soil quality?
- Organic Matter: decompose OM + build OM
- Decomposition of surface residue and OM
- Structure/aggregate stability: by decomposing OM + burrowing/excreting
- Humification: breaking down OM into a more stable form
- Nitrate leaching: facilitate the processes of nitrification, N-fixation, and denitrification
- Nutrient cycling: break down chemical bonds to convert unavailable forms of minerals into soil nutrients that are in available forms for plants
9 functions of soil organisms (how they are classified) + at least 2 examples of each
- photosynthesizers - plants, algae, bacteria
- decomposers - bacteria, fungi
- mutualists - bacteria, fungi
- pathogens - bacteria, fungi
- parasites - nematodes, micro-arthropods
- root-feeders - nematodes, macroarthropods
- bacterial-feeders - protozoa, nematodes
- shredders - earthworms, arthropods
- higher level predators - nematode-feeding nematodes, larger arthropods
4 components of living soil? + definitions
- Living organisms: the part of the soil that is still alive like plants and their roots, fungi, bacteria, nematodes, arthropods, protozoa
- Fresh residue: OM that resides on the soil surface after organisms have died; fungi, root-feeder nematodes + bacteria feed on this aka DETRIVORES
- Active Fraction: OM that is partially or actively being decomposed. A lot of nutrients stored in previously alive organisms are released back into the soil.
- Stabilized OM (Humus): OM that has been decomposed to a state in which it cannot be decomposed further because the bonds are too chemically complex for most organisms to break them down or the particles are physically protected inside soil aggregates making this fraction very stable.
Labile OM
OM that is easily decomposed
Root exudates
soluble sugars, amino acids, and compounds secreted by plant roots
particulate OM/light fraction OM
thought to represent the active fraction of OM; larger and lighter than other types of OM
lignin
hard to decompose compound part of the fibres of older plants, usually wood
fungi can use the carbon ring structures in lignin as food
recalcitrant OM
OM that only few organisms can decompose - like lignin or humus
humus or humified OM
- complex OM that has been decomposed so much that not many organisms can continue to break it down - either too chemically complex or physically hidden in aggregates
- very stable
- very important in building tiny aggregates and improves water + nutrient holding capacity
list and define the 5 species of soil organisms
- Arthropods
- Bacteria
- Fungi
- nematodes
- protozoa
Define Arthropods
invertebrate animals with jointed legs
includes insects, crustaceans, arachnids, etc.
Define Bacteria
microscopic, single-celled organisms that are mostly non-photosynthetic (except cyanobacteria + actinomycetes)
Define fungi
multi-celled, non-photosynthetic organisms that are neither plants nor animals
fungal cells form long chains called hyphae and many reproductive fruiting bodies (mushrooms or molds)
some fungi are single-celled - ex. yeast
2 different kinds of fungi: saprophytic + mycorrhizal
What are the 2 different kinds of fungi? What do they do?
- Saprophytic: decompose dead OM
- Mycorrhizal: form symbiotic associations with plant roots - they supply the plant nutrients in exchange for energy from the plant
T or F: soil organisms are distributed uniformly throughout the soil
FALSE - they occur where they can find appropriate space, nutrients, and water and definitely where the is OM.
Usually though within the top few inches of the soil
What is the function of photosynthesizers and who is a photosynthesizer?
CAPTURE ENERGY from the sun to fix CO2
add OM to soil (fallen leaves, dead roots, dead plants)
-plants, algae, bacteria
What is the function of decomposers? Who is a decomposer?
BREAK DOWN RESIDUE
- immobilize nutrients
- create new organic compounds to make nutrients available to plants
- produce compounds that help with aggregate stability
- bind soil aggregates with fungal hyphae
- nitrifying and denitrifying bacteria convert nitrogen
- compete with or inhibit disease-causing organisms
bacteria + fungi
What is the function of a mutualist? Who is a mutualist?
ENHANCE PLANT GROWTH
- mycorrhizal fungi form symbiotic relationships with some plant roots to supply them with nutrients for growth
- some bacteria fix N2
- protect plants from disease-causing organisms
bacteria +fungi
What is the function of a pathogen? who is a pathogen?
PROMOTE DISEASE
- consume roots and other plant parts to cause diseases
bacteria + fungi
What is the function of a parasite? who is a parasite?
PROMOTE DISEASE
- parasitize nematodes or insects, including disease-causing organisms
nematodes + microarthropods
What is the function of a root-feeder? who is a root-feeder?
CONSUME PLANT ROOTS
-potentially cause significant crop yield losses
nematodes and macroarthropods
What is the function of a bacterial-feeder? who is a bacterial-feeder?
GRAZING
- release plant available nitrogen (NH4) and other nutrients are released when they feed on bacteria
- control many root-feeding or disease-causing pests
- stimulate and control the activity of bacteria
protozoa + nematodes
What is the function of fungal-feeders? who are they?
GRAZING
-release plant available nitrogen (NH4) and other nutrients
- control root feeders and disease pests
- stimulate and control population of fungi
nematodes and microarthropods
What is the function of shredders? who are they?
BREAK DOWN RESIDUE + ENHANCE SOIL STRUCTURE
- shred plant litter as they feed on bacteria and fungi
- provide habitat for bacteria in their guts and fecal pellets
- enhance soil structure as they produce fecal pellets while burrowing through the soil (their casts are tiny aggregates)
nematode-feeding nematodes and larger arthropods
5 places organisms are found in the soil, who is found where and what are they doing there?
- Rhizosphere: plant roots, bacteria, protozoa, nematodes - most of the nutrient cycling + disease suppression of plants occurs here
- Plant litter: fungi, bacteria, shredders - hyphae sends N to litter layer + fungi break down the complex carbon structures; bacteria break down less complex carbon compounds in the surface residue; shredders break up plant litter into smaller pieces to benefit fungi and bacteria
- Humus: fungi - makes enzymes that can decompose the complex compounds in humus
- Surface of soil aggregates: aerobic bacteria, fungi, earthworms - `
- Spaces between soil aggregates: arthropods, nematodes, protozoa - cannot burrow through aggregates so they burrow in the pores between to move
T or F: microbial biomass decreases with depth?
TRUE
when are soil organisms active in temperate systems?
late spring when the temperatures and moisture conditions are optimal for growth
Define the structure of a food web
the composition and relative numbers of organisms in each group within the soil system
What organisms dominate agricultural and grassland food webs?
bacteria
What organisms dominates forest food webs?
fungi - much more so in coniferous
Give an example of organisms reflecting their food source?
bacterial-feeding nematodes will be more abundant in a bacterial-dominated food web than fungal-feeding nematodes
Give an example of a land mgmt. practice that changes food webs?
reduced tillage in agricultural soils will increase the ratio of fungi to bacteria, as well, earthworms + arthropods will become more abundant
What are the 2 methods of counting food web components? Which groups can be counted?
- direct counts: counting individuals you can see with your eye or a microscope
- plate counts: count number of bacterial or fungal colonies grown from a soil sample
bacteria, protozoa, arthropods, and nematodes
What are the 3 measurements of food web activity/biological activity?
- respiration: measuring CO2 production from soil organisms
- nitrification rates: measuring the activity of those species involved in converting ammonium to nitrate (nitrification)
- decomposition rates: measuring the speed of disappearance of OM
What are cellular constituents? How are they measured? (4)
the total biomass of all soil organisms or specific characteristics of the community can be inferred by measuring components of the orgs
- Biomass, carbon, nitrogen or phosphorous: measuring the amount of nutrients in living cells to estimate total biomass
- Enzymes: measuring enzymes in live cells or attached to soil
- Phospholipids + other lipids provide a “fingerprint” of the community and quantify the biomass of groups like fungi or actinomycetes
- DNA + RNA: also provide a fingerprint of the community and can detect the presence of specific species or groups
What is food web complexity? Give an example
the number of different functional groups of soil organisms - diversity
ex. a soil with 10 species of bacterial-feeding nematodes is less complex than a soil with 10 nematode species that include bacterial, fungal, and predatory nematodes
What can alter food web complexity?
land management practices that alter the structure of the soil
ex. crop selections, tillage, residue management, pesticide use, irrigation
6 benefits of soil complexity?
- Nutrient cycling
- nutrient retention
- Improved structure, infiltration and water-holding capacity
- disease suppression
- degradation of pollutants
- biodiversity
What is successful land management? Give examples of ways to maintain soil health
requires techniques that protect all resources, soil water, air, organisms, and humans.
- increasing crop rotation and diversity can increase food sources and variety of soil organisms that enhance crucial soil processes
- breaking up agricultural fields to create more habitats for arthropods
- reduced use of pesticides will prevent a decline in food web complexity
how is carbon sequestered in the soil for decades-hundreds of years?
carbon is sequestered in the soil as ORGANIC MATTER.
as soil orgs decompose OM, they release carbon into the atmosphere as CO2 or convert it to a variety of forms of OM.
Stable forms of OM (humus) can stay in the soil for hundreds of years as it can be protected inside soil aggregates and cannot physically be reached or chemically broken down further as it is too complex
