The rate of decomposition of organic matter is negatively affected by the presence of

Correct option is C

The correct answer is (C) Lignin

Explanation:
• Decomposition is the process by which soil organisms break down organic residues into simpler compounds. The speed of this process depends on the chemical composition of the material.
• Lignin is a complex, large structural polymer found in the cell walls of plants (especially woody tissues). It is extremely resistant to microbial attack due to its irregular structure and strong chemical bonds.
• Materials high in lignin decompose very slowly. Lignin also physically protects cellulose and hemicellulose from enzymes, further slowing the process.
• Therefore, a high lignin content has a strong negative correlation with the rate of decomposition.

Information Booster:
• [Image comparing the decomposition speed of different organic compounds: sugars > proteins > cellulose > lignin]
• The C:N ratio also affects decomposition; a high C:N ratio (low nitrogen) slows the process because microbes lack the nitrogen needed to build their populations.
• Lignin is a precursor to the formation of stable soil humus.

Additional Knowledge:
• Protein (Option A) and Water-soluble compounds (Option D): These are 'labile' fractions and are decomposed very rapidly by soil microbes.
• Fats and Waxes (Option B): These are more resistant than proteins but much less resistant than lignin.