Soil microorganisms and soil health — A/L Biology

What must I remember about Soil microorganisms and soil health?

• Soil health is the sustained capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans, maintained largely by the biodiversity and biochemical activity of soil microorganisms.
• The Rhizosphere is the narrow zone of soil immediately surrounding plant roots (1-2 mm), enriched in root exudates (sugars, amino acids, organic acids) that support microbial densities up to 100 times higher than bulk soil.
• Decomposition and Humus formation: Soil fungi (saprotrophic Basidiomycota, Ascomycota) and Actinobacteria break down recalcitrant polymers (lignin, cellulose, hemicellulose) to synthesize stable colloidal Humus, enhancing soil cation exchange capacity (CEC) and moisture retention.
• Biogeochemical mobilization of essential nutrients: Biological nitrogen fixation (Rhizobium, Frankia, Nostoc), Phosphorus solubilization (phosphate-solubilizing bacteria Pseudomonas and Bacillus secreting gluconic acid), and Mycorrhizal symbiosis (VAM / AM fungi increasing phosphorus and micronutrient uptake).
• Biocontrol and Plant Growth-Promoting Rhizobacteria (PGPR): Soil microbes suppress soilborne phytopathogens through competitive exclusion, production of siderophores (chelating iron), antibiotics, and systemic acquired resistance (SAR) induction.

Test yourself (1 minute)

1. Vesicular-Arbuscular Mycorrhizae (VAM / AMF)

   Glomeromycota fungi penetrate root cortical cells forming branched arbuscules (nutrient exchange sites) and storage vesicles; vastly increase effective root absorption surface area for immobile phosphate ions.

2. Actinobacteria role

   Filamentous Gram-positive bacteria (e.g., Streptomyces) that degrade complex organic matter, produce soil odor geosmin, and synthesize critical clinical antibiotics.

3. Soil microbial biomass indicator

   Active soil microbial biomass carbon (SMBC) serves as the most sensitive early biological indicator of soil degradation, pesticide toxicity, or regenerative restoration.

Practise Soil microorganisms and soil health questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 9

What should I study first?

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Where does Soil microorganisms and soil health fit in the syllabus?

Year 2 · Term 3