Question

The most abundant soil microorganism is:

• A. Bacteria
• B. Nematodes
• C. Fungi
• D. Earthworm

Hint:

Remember the general abundance hierarchy of soil microbes by population size:
Bacteria \( > \) Actinomycetes \( > \) Fungi \( > \) Algae \( > \) Protozoa.
Bacteria are always the highest in absolute cell numbers.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Soil hosts a highly diverse and dense biological community comprising bacteria, fungi, actinomycetes, algae, protozoa, nematodes, and earthworms.
These organisms are classified by their abundance in terms of absolute cell numbers or total biomass per unit weight of soil.

Step 2: Detailed Explanation:
In terms of absolute numbers (cell count per gram of soil), bacteria are by far the most abundant microorganisms in soil.
A single gram of fertile surface soil can host between \( 10^8 \) to \( 10^9 \) bacterial cells.
They are single-celled prokaryotic organisms that multiply rapidly under favorable moisture, temperature, and nutrient conditions.
They play a vital role in soil organic matter decomposition, nutrient cycling, and biochemical transformations (such as nitrification and nitrogen fixation).
While fungi (C) are highly significant and often dominate the total soil microbial biomass in acidic forest soils, their absolute cell numbers are much lower than those of bacteria due to their larger, multicellular hyphal structure.
Nematodes (B) and earthworms (D) are multicellular soil fauna and are present in much lower numbers compared to unicellular microorganisms.

Step 3: Final Answer:
Bacteria is the most abundant soil microorganism.