SOIL ecology

What is soil?

Mixture of broken rocks, minerals, living organisms and decaying organic matter (humus), air and water

Types of organisms in soil

Decomposers

Root feeders

Shredders

Parasites

Predators

Example of root feeders

nematodes

Examples of shredders

Mites

Example of parasites

round worms, hook worms and whip worms

Example of predators

Beetles and spiders

What is the source of energy in the soil?

Detritus (decaying organic matter), which is ultimately derived from the sun

Detritus vs humus

Detritus (earlier stage or decomposition)

Humus (later stage of decomposition)

What are the abiotic factors that affect the biodiversity of soil?

Water

Mineral salts (Nitrates, phosphate, potassium salt)

pH

Temperature

How does mineral salts affect biotic factors?

Soil organisms help break down organic materials, releasing mineral salts in forms plant can use. In turn, plants and soil organisms rely on mineral salts for essential functions like energy production and nutrient cycling.

How does pH affect biotic factors?

Maintaining a balanced pH that is neither too acidic nor alkaline is imporant for ensuring the optimal functioning of the soil ecosystems. This is because important processes like decomposition carried out by bacteria/fungi requires an optimum pH. This in turn results in efficient nutrient cycling and healthy plant growth

How does water effect biotic factors?

Water acts as a medium that enables soil organisms to carry out their life processes and promote plant growth via symbiosis and disease suppression

How does temperature affect biotic factors of soil?

Most organisms are active between 0 degrees Celsius and 40 degrees Celsius, as there is a minimum and maximum temperature beyond which they cannot carry out their vital life processes.

Within this range, there is an optimum temperature at which they are most active, and this is required for vital processes

This ensures efficient nutrient cycling and plant growth.

Biotic factors that affect biodiversity of soil

Decomposers

Nematodes

Spring tail

Worms

Rhizobium

Explain decomposers (bacteria)

Decomposes organic matter in the earlier stage (later stage fungi tends to dominate)

Explain mutualism of bacteria in soil

Extracts nitrogen gas from the air and convert it into forms that plants can use (nitrogen fixers)

Elab decomposers (fungi)

Saprophytic fungi - decompose organic matter into mineral nutrients (e.g. ammonium, nitrate, phosphate) - taken up by plants

Helps to increase accumulation of humic-acid rich organic matter that is resistant to degradation and stays in soil for a long time.

Explain mutualism for fungi

Mycorrhizal fungi

• The hyphae penetrate deeper into the soil to access soil zones that roots cannot penetrate alone to absorb nutrients and water.

• Plants provide fungi with carbohydrates, while the fungi provides the plant with phosphate, nitrate and other minerals.

State some nematode roles

Bacteria feeders

fungal feeders

Predatory nematodes

Omnivores

Beneficial

Elab nematodes (bacteria)

Bacteria feeders:

• Elaphonema release plant-available nitrogen when they consume bacteria

Elab nematodes (fungi)

Nematodes puncture cell walls of fungal hyphae and withdraw cell fluid. This releases plant-available nitrogen from fungal biomass

Elab nematodes (predatory)

Predatory nematodes

• Predatory nematode consumes a smaller nematode

Elab nematodes (omnivores)

Omnivores:

• Root-feeding nematodes use their styleys to puncture the thick cell wall of plant root cells and siphon off the internal contents of the plant cell

• Causes economically significant damage to crops

Elab nematodes (beneficial)

Help

• Regulate population of soil organisms

• Mineralise nutrients into plant-available forms (e.g. excrete nutrient rich waste)

• food source for other soil organisms

• consume disease-causing organisms

Elab worms (what do they do)

The earthworm burrows within the soil, allowing for air and water to reach the roots of plants. This allows nutrients to be able to reach deep within the soil.

Earthworms are detritivores and they consume dead and decaying matter, like dried leaves. This allows for nutrient cycling to occur, returning complex organic matter into simple inorganic matter for the plants to use.

Importance of insects in soil (e.g. springtails)

Source of food for larger organisms. This enriches the ecosystem with a greater diversity and allow for more complex food webs, resulting in a more stable ecosystem. Some insects also act as vectors and are able to carry other microorganisms to populate other areas.

After eating, they produce many small faecal pellets which increase the surface area of partially decomposed material that can be colonised by primary decomposers, bacteria and fungi. The faeces are important source of nitrates in forest soil.

Elab rhizobium sp. (nitrogen fixing bacteria)

• They convert atmospheric nitrogen into nitrate that plant use to make proteins

Elab rhizobium mutual relationship

• Bacteria convert nitrogen into nitrate for the plants and in return receive nutrients.

• They also have a place to reside in the roots

Why do plants need nitrate?

Make proteins

How do soil organisms prevent erosion? (understand this)

Improves soil structure. They enhance soil aggregation, bind the soil with roots, decompose organic matter to add humus, and create pore spaces that increase water infiltration.

How do soil organisms drive decomposition of organic matter? (understand this)

They recycle nutrients and enhance soil fertility

• The organisms break down organic matter, releasing nutrients that form humus. Humus provides essential nutrients for and supports underground animals like worms and ants by providing a habitat and food supply.

What causes soil damage? (understand this)

caused by factors like pollution and erosion

Why is soil damage so bad? (understand this)

This depletes essential nutrients → soil microorganisms vital for decomposition and soil regeneration die → organic materials are not decomposed → soil formation stops → ecosystem unable to recover.

This loss affects all organisms dependent on healthy soil for habitat and resources.

Eutrophication process

When excess fertilisers (esp nitrates and phosphates), can run off into rivers and lakes.

Phosphate usually limit growth of plant and algae. When extra phosphate enter, especially with nitrates, algae multiply rapidly, blocking sunlight. This prevents aquatic plants from photosynthesising and producing oxygen, leading to their death and harming aquatic animals. Decomposition of dead organisms further depletes oxygen, making the water uninhabitable.