Nitrogen Cycle

Alfisols

UNDER FORESTS! temperate humid and subhumid regions (southern IL); moderately leached soils with relatively high native fertility

Sizes of soil organisms

macrofauna (>2mm), mesofauna (0.01-2mm), microfauna (<0.1mm)

Functional diversity

presence of several organisms who carry out a wide array of biochemical processes

Functional redundancy/equivalence

presence of several organisms who each carry out thousands of enzymatic and physical processes; multiple species share similar or identical roles in ecosystem functionality --> leads to stability and resilience

Stability

the ability of soils to continue to perform functions

Resilience

the ability of soil to bounce back to functional health after a severe disturbance has disrupted normal processes

Genetic resources

yeasts and antibiotics; biodiversity in soils often greater than above soils

primary producers

vascular plants

primary consumers

-herbivores
-detritivores

herbivore

organisms consume live plants

detritivore

organisms feed on detritus (dead tissues of primary producers)

secondary consumers

organisms feed on the bodies of primary consumers

microbivorous feeders

animal that eats microbes (bacteria) as their primary food source; secondary consumers

mycrophytic feeders

use microflora as food source

Meso- and Micro-Fauna Decomposition Stimulation

1. 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. 2. chewed plant tissues are thoroughly mixed with microorganisms in the animal gut, where conditions are ideal for microbial activity 3. mobile animals carry microorganisms with them and help the latter to disperse and find new food sources to decompose.

Burrowing animals

• termites, earthworms, rodents
• make subsoil channels
• affects bulk density, % porosity, CO2 diffusion, Ksat, infiltration, percolation, and drainage

Earthworms

-consume detritus and organic matter (weight of soil equal to 2-30x their own weight per day

• burrows help plant roots penetrate soils

epigeic earthworm

live in the litter layer of OM rich soils

endogeic earthworm

move in horizontal burrows

anecic earthworm

vertical burrows

Earthworm Casts

earthworms ingest soils and expel them as globular soil aggregates
-high in polysaccharides that cause good aggregate stability
-increases soil aeration and drainage by forming macropores while increasing water retention
-mixing activity can alleviate compaction

Nutrients in earthworms

1. soils and organic matter are well digested by enzymes and host microflora in earthworms
2. worms assimilate N, P, and S into their body structures that can be released as a nutrient source when they die

Earthworms Expose Soil Surfaces

1. remove crop residue cover leaving surface soils bare of residues while building middens (plant residues + castings surrounding the opening of a worm burrow)
2. exposed soils vulnerable to erosion and crust formation

Earthworms Increase Chemical Leaching

Anecic worm vertical burrows carry percolating water downwards rapidly
-water transports pollutants downwards into groundwater

Dung beetles

bury animal dung in the soil
-protects nutrients from easy loss by runoff or volatilization
-good for nutrient cycling

Soil Species Importance ID

1. Abundance (3 of orgs)
2. weight/biomass per unit volume of soil
3. metabolic activity

Ants

located in humid regions to semiarid grasslands; nest building activity improves soil aeration, infiltration, and nitrogen cycling

Termites

-widely distributed across 2/3 of the world
-breakdown organic materials in soils
-extensively transport subsoils to the surface and mix plant residues with soils to build mounds
-may attract plant communities as resulting soils from mounds are high in clay, nutrients, and OM

Termite mounds

build mounds and incorporate large quantities of soil into them

1. Support column
2. spiral foundation block
3. larvae chambers
4. sustainable monoculture fungus farming --> symbiotic relationship w fungi who will digest cellulose for them
5. food storage areas
6. queen's chamber
   7+8. underground tunnels to maintain humidity and transport food/building materials

Nematodes

microfauna (4-100 micron), have relatively large populations in sandy, moist, or well-aggregated soils where they can move easily
-consumers

Nematode Effect on Plant Available N (Bacteriovors)

Nematodes consume bacteria, whose cells have more nitrogen than they can actually use. Soluble nitrogen is released into soils --> mineralization
-More N released with nematodes than without from graph

Protozoa

unicellular eukaryotic organisms (6-100micron); most varied but most numerous
-feed on soil bacteria (secondary to higher level consumers), indirectly control OM decay by controlling bacteria populations

What are simple exudates in plants?

Substances that leak out from plant cells.

What are secretions in the context of plants?

Simple compounds released by metabolic processes.

What are plant mucilages?

Complex organic molecules that originated from plant or bacteria degradation.

Mucigel

gel-like substance that helps a root push through the soil

What are higher plants a primary source of?

Organic matter

What percentage of soil volume do plant roots occupy?

1%

What percentage of total soil respiration is attributed to plant roots?

25-33%

How do plant roots stabilize soil aggregates?

By taking up water and stabilizing the organic mineral bonds

What effect does water uptake by plant roots have on soil?

It encourages soil shrinkage and cracking

Rhizosphere

zone of soil influenced by living roots, roughly 2mm out from root surface
-makes chemical and biological characteristics different from bulk soil (increased or decreased soil acidity)

Rhizodeposition

chemical additions to soil; three types of organic compounds
-solubilize nutrients = plant uptake
-support and facilitates colonization of bacteria

Low molecular weight organic compounds

organic acids, sugars, amino acids, and

High-molecular mucilages

secreted by root-cap cells and epidermal cells

Sloughed off cells

sourced from root cap and epidermis

Soil Algae

Photoautotrophic and eukaryotic organisms (2-20 micron)--> photosynthesize to create their own food
-colonize at the soil surface
-become OM inputs and produce polysaccharides to stabilize soil aggregates
-prefer moist to wet conditions

Types of Soil Algae

1. green
2. yellow-green
3. diatoms

Microbiotic crusts

important in arid and semi-arid regions by reducing evaporation and erosion

Soil Fungi

microfauna (<0.1mm)

1. yeast
2. mold
3. mushroom fungi
   -decompose OM
   -facilitate humus formation
   -enhance aggregate stability and soil fertility

Other fungi activities

-enhance structure for soil tilth (ease of tillage)
-predator
-produce complex organic compounds
-penicillium species produce modern antibiotic drug

Mold and fungi

filamentous, hyphae and mycelia (twisted hyphae)

Molds

develop in all pH ranges

Mushroom fungi

edible or poisonous
-hyphae penetrate soils and organic residues
-some species help decompose woody tissues

Mycorrhizae

association between fungi and plant roots; beneficial symbiotic relationship
-Fungi receive sugars, plants receive root system extension

How do plants benefit from mycorrhizae?

Absorption surface of infected roots are 10 times greater than the root system of an uninfected plant, so better nutrient uptake occurs and sometimes protection from pathogens

True or False: Mycorrhizae enhance nutrient uptake for plants

True

Endomycorrhizae

penetrate root cortex cells and set up finely branched, microscopic intracellular interfaces inside them

Ectomycorrhizae

grows around the root and between cortical cells (NOT PENETRATIVE)

Arbuscules

highly branched hyphae structures

Vesicles

storage organs

Soil Bacteria

single-celled prokaryotic organisms, (0.5-5micron)
-autotrophic or heterotrophic
-used for environmental remediation
-fix atmospheric nitrogen
-extremely numerous

What are Actinomycetes?

Filamentous organisms similar to fungi.

Are Actinomycetes prokaryotic or eukaryotic?

Prokaryotic (no nuclear membrane).

What is the size range of Actinomycetes?

0.5-5 microns.

What type of metabolism do Actinomycetes have?

Aerobic heterotrophs.

Where do Actinomycetes live?

On decaying organic matter in moist soils.

What role do Actinomycetes play in the ecosystem?

They decompose organic matter, liberating soil nutrients.

What do Actinomycetes produce that is significant for medicine?

Antibiotic compounds.

First Condition Affecting Soil Microorganism Growth

OM Requirements
-used as energy source by heterotrophs
bacteria can degrade sugars/starches
fungi and actinomycetes can degrade cellulose and lignin

Second Condition Affecting Soil Microorganism Growth

Oxygen Requirements
Aerobic organisms need oxygen for electron acceptor
-anaerobic organisms use other substances
-Facultative bacteria use anaerobic or aerobic metabolism

Third Condition Affecting Soil Microorganism Growth

Moisture and Temperature
-optimum moisture level = potential of -10 to -70kPa
-temp range = 20-40 degrees C

Fourth Condition Affecting Soil Microorganism Growth

Exchangeable Ca and pH
-high Ca and near neutral pH
-calcium = "general reset"

Plant pests and parasites

nematodes and insect larvae (soil fauna) feed on plants

Sting nematode

On bermudagrass, cause tufted root growth on root times, swollen root terminals, inhibited root growth, and root necrosis

Plant disease

microflora of fungi are most responsible for soil-borne crop disease

Plant Disease control

-quarantine system
-crop rotation and tillage
-Lower pH can control actinomycetes
-Air and temp management (wet, cold conditions favor rotting and diseases
-good drainage, planting on ridges
-solarization