Question

What is the final state of dead plant material and animal residues after complete decomposition?

1. They completely evaporate, leaving no residue.
2. They are gradually decomposed until their original identity is no longer recognizable, at which point they are considered soil organic matter (SOM).
3. They are transformed into living microbial biomass and remain as such indefinitely.

• A. 3 only
• B. All
• C. 1 only
• D. 2 only

Answer 1

Answer:

D. 2 only

• Leaching by water transfers soluble materials away from decomposing organic matter into the soil matrix. These soluble materials are absorbed by organisms, react with the mineral phase of the soil, or are lost from the system in solution.

• Fragmentation by soil animals breaks large pieces of organic matter into smaller ones, which provide a food source for soil animals and create fresh surfaces for microbial colonization. Soil animals also mix the decomposing organic matter into the soil.

• Chemical alteration of dead organic matter is primarily a consequence of the activity of bacteria and fungi, although some chemical reactions also occur spontaneously in the soil without microbial mediation.

• Dead plant material (litter) and animal residues are gradually decomposed until their original identity is no longer recognizable, at which point they are considered soil organic matter (SOM).