Question

Which of the following microflora is most abundant in soil?

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

Hint:

Remember the distinction:
Highest Numerical Abundance $\rightarrow$ Bacteria
Highest Total Biomass in acidic/forest soils $\rightarrow$ Fungi

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Soil biology examines the diverse community of living organisms inhabiting the soil matrix, collectively referred to as the soil food web.
These organisms are classified based on their size into microflora (bacteria, fungi, actinomycetes, algae), microfauna (protozoa), mesofauna (nematodes, collembola), and macrofauna (earthworms, insects).
The microflora represent the primary decomposers and nutrient cyclers in the soil.
When evaluating which group is most abundant, we must distinguish between numerical abundance (population count per unit mass of soil) and biomass abundance (total weight of organisms per unit mass of soil).

Step 2: Detailed Explanation:
In terms of numerical abundance, Bacteria are by far the most abundant group of microflora in soil systems.
Under healthy, fertile soil conditions, one gram of agricultural soil can contain between \(10^8\) to \(10^9\) (one hundred million to one billion) individual bacterial cells.
This extreme abundance is due to their small size (typically \(0.5\text{ to }2.0\ \mu\text{m}\)), rapid reproduction rate (binary fission occurring every few hours under ideal conditions), and metabolic versatility, allowing them to occupy diverse ecological niches in micro-aggregates.
Let us compare this with the other listed groups:
1. Fungi:
While fungi have a much greater total biomass in most soils (due to their extensive network of hyphae), their numerical count (measured as fungal propagules or colony-forming units) is significantly lower than that of bacteria, typically ranging from \(10^5\) to \(10^6\) per gram of soil.
2. Viruses:
Although viruses (specifically bacteriophages) are numerically abundant in soils, they are obligate intracellular parasites and are generally classified as non-living genetic elements rather than active soil microflora.
3. Nematodes:
Nematodes are microscopic roundworms belonging to the soil mesofauna (not microflora).
Their population size is significantly smaller, typically ranging from \(10\text{ to }100\) individuals per gram of dry soil.

Step 3: Final Answer:
Therefore, numerically, Bacteria represent the most abundant group of microflora present in the soil.