Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Carbon mineralization is tightly coupled to the release of minerals N, P, and S
Reason (R) : It is driven by microbial requirements for C and nutrients for their maintenance, growth, and the production of extracellular metabolites including enzymes
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Biogeochemical cycles of C, N, P, and S are biologically linked because soil decomposers require all these elements in stoichiometric ratios (C:N:P:S ratio) to grow and reproduce.
This makes (R) the correct explanation of (A).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Mineralization is the microbial conversion of elements from organic forms (bound in plant/animal residues) to inorganic mineral forms (such as \(\text{NH}_4^+\), \(\text{NO}_3^-\), \(\text{H}_2\text{PO}_4^-\), \(\text{SO}_4^{2-}\)) that can be absorbed by plant roots.

Step 2: Detailed Explanation:
Let us analyze both statements:
- Assertion (A): "Carbon mineralization is tightly coupled to the release of mineral N, P, and S."
This is correct.
Organic matter consists of complex macromolecular complexes where carbon is bound covalently to nitrogen, phosphorus, and sulfur.
During decomposition, as carbon is mineralized to carbon dioxide (\(\text{CO}_2\)) through microbial respiration, the associated N, P, and S are simultaneously mineralized and released into the soil solution.
- Reason (R): "It is driven by microbial requirements for C and nutrients for their maintenance, growth, and the production of extracellular metabolites including enzymes."
This is also correct.
Soil microorganisms decompose organic residues to satisfy their physiological requirements for carbon (energy and biomass) and mineral nutrients (essential elements like N, P, S).
To access these elements, microbes synthesize and excrete extracellular enzymes that break down organic polymers.
Since microbial metabolic activity drives the simultaneous breakdown of organic compounds to meet nutrient requirements, this process couples carbon mineralization with the release of N, P, and S.
Therefore, both statements are true, and (R) is the correct biological explanation of (A).

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).