Fungi and Microorganisms in the soil

Fungi in Soil

What are Fungi?

Eukaryotic organisms, can

be unicellular yeasts or

multicellular filaments

Prefer low pH and high C/N

ratio environments

Examples: Amanita,

Tricholoma, Verticillium,

Phytophthora

Types of Fungi in Soil

Decomposers: Break down

organic matter, recycle

nutrients

Mutualists: Form

mycorrhizal symbiosis with

plants, provide minerals in

exchange for carbon

Pathogens: Cause diseases

in plants

Positive Effects of Fungi

Stabilize soil aggregates

Beneficial mycorrhizal

associations with plants

Decompose woody residues

using nitrogen

Protect plants against pests

and drought

Produce antibiotic

compounds

Negative Effects of Fungi

Pathogenic fungi cause

plant diseases

Affect competitive balance

between plant species

Actinomycetes in Soil

What are Actinomycetes?

Filamentous gram-positive

bacteria

Abundant in neutral to

alkaline soils

Size ranges from 0.5 to 1.5

μm

Examples: Streptomyces,

Micromonospora

Positive Effects of

Actinomycetes

Decompose resistant

organic material

Contribute to carbon and

nitrogen cycles

Fix nitrogen for host plants

Produce plant growth

regulators

Act as biocontrol agents

Negative Effects of

Actinomycetes

Affect diversity of other

microorganisms

Some species cause plant

diseases

Microorganisms Found in Soil

Introduction

Soil harbors a diverse group

of microorganisms due to

the variety of nutrients and

conditions present.

Major groups include

bacteria, fungi, viruses,

actinomycetes, protozoa,

cyanobacteria, and

nematodes.

Number and composition

changes with soil depth and

conditions like moisture,

nutrients, etc.

Rhizosphere has more

microorganisms than bulk

soil.

Bacteria

Definition: Prokaryotic,

unicellular, microscopic

organisms. Common shapes

include rods, spheres, and

spirals.

Abundant in soil, especially

rhizosphere. Up to 108-109

bacteria per gram soil.

Examples: Bacillus,

Pseudomonas, Clostridium,

Corynebacterium

Positive Effects: Nutrient

cycling, soil structure

improvement, succession

facilitation

Negative Effects:

Pathogenic strains can

reduce crop health and

yields

Fungi

Definition: Eukaryotic

organisms like molds,

yeasts, mushrooms.

Filamentous growth in soil.

Biomass ranges from 100-

1500 kg/ha. Up to 105

fungal species in a gram of

soil.

Examples: Aspergillus,

Penicillium, Fusarium,

Trichoderma

Positive Effects: Organic

matter decomposition,

nutrient cycling, soil

structure

Negative Effects: Some

cause plant diseases,

mycotoxins

Actinomycetes

Filamentous bacteria,

intermediate between

bacteria and fungi.

Abundant.

Examples: Streptomyces,

Nocardia

Positive Effects: Antibiotic

production, organic matter

decomposition

Negative Effects: Some

pathogenic, cause root rot

Protozoa

Microscopic eukaryotic

organisms. Feed on bacteria

and fungi.

Examples: Amoeba,

paramecium, ciliates

Positive Effects: Nutrient

mineralization, prey on

pathogens

Negative Effects: Some

parasitic species

Cyanobacteria

Photosynthetic prokaryotes.

Fix atmospheric nitrogen.

Examples: Nostoc,

Oscillatoria

Positive Effects: Nitrogen

fixation, carbon

sequestration

Negative Effects: Some

toxin-producing strains

Viruses

Infect bacteria, fungi, algae.

Very diverse.

Positive Effects: Gene

transfer between microbes

Negative Effects: Kill host

cells

Nematodes

Microscopic roundworms.

Abundant and diverse.

Examples: Root-knot, cyst,

stubby root nematodes

Positive Effects: Nutrient

cycling, prey on pathogens

Negative Effects: Some

parasitic varieties damage

roots

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