3.2 Soil food web and microbial life

Soil is alive with a complex web of microorganisms, from bacteria to fungi to tiny animals. These critters work together, breaking down organic matter, cycling nutrients, and forming partnerships with plants. It's a bustling underground city!

Understanding this hidden world is key to healthy soil and thriving plants. By nurturing beneficial microbes and their relationships, we can boost soil fertility, plant growth, and overall ecosystem health naturally.

Soil Microorganisms

Bacteria and Fungi

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• Bacteria are prokaryotic microorganisms that play a crucial role in soil health by breaking down organic matter, fixing nitrogen, and improving soil structure
• Soil bacteria can form symbiotic relationships with plants (rhizobia) to fix atmospheric nitrogen and make it available for plant uptake
• Fungi are eukaryotic microorganisms that decompose complex organic compounds in the soil, such as lignin and cellulose
• Fungi form extensive networks of hyphae in the soil, which help to improve soil structure, water retention, and nutrient transport

Protozoa and Nematodes

• Protozoa are single-celled eukaryotic organisms that feed on bacteria, fungi, and other microorganisms in the soil
• Protozoa help to regulate microbial populations and release nutrients through their feeding activities
• Nematodes are microscopic roundworms that can be beneficial or harmful to plants depending on the species
• Beneficial nematodes feed on bacteria, fungi, and other soil organisms, contributing to nutrient cycling and pest control

Arthropods

• Arthropods are invertebrate animals with exoskeletons, such as insects, spiders, and mites
• Soil-dwelling arthropods, like springtails and mites, aid in decomposition by breaking down organic matter and facilitating microbial activity
• Some arthropods, such as predatory mites and beetles, help control pest populations in the soil

Beneficial Soil Relationships

Mycorrhizae

• Mycorrhizae are symbiotic associations between certain fungi and plant roots
• In this relationship, the fungus receives carbohydrates from the plant, while the plant benefits from increased nutrient and water uptake facilitated by the fungal hyphae
• Mycorrhizal associations can improve plant growth, stress tolerance, and disease resistance

Rhizosphere and Symbiosis

• The rhizosphere is the narrow region of soil directly influenced by plant root secretions and associated soil microorganisms
• Plants release exudates containing carbohydrates, amino acids, and other compounds that attract and support beneficial microorganisms in the rhizosphere
• Symbiosis refers to mutually beneficial relationships between different organisms, such as plants and microorganisms (rhizobia, mycorrhizae) or between different microorganisms in the soil

Soil Processes

Nutrient Cycling

• Nutrient cycling is the process by which nutrients move through the soil, living organisms, and the environment
• Soil microorganisms play a vital role in nutrient cycling by decomposing organic matter, releasing nutrients, and making them available for plant uptake
• Important nutrient cycles in the soil include the carbon cycle, nitrogen cycle, and phosphorus cycle

Decomposition

• Decomposition is the breakdown of dead organic matter into simpler compounds by microorganisms and other soil organisms
• The decomposition process releases nutrients back into the soil, making them available for plants and other organisms
• Factors affecting decomposition rates include temperature, moisture, pH, and the quality of the organic matter (carbon-to-nitrogen ratio)