Decomposition of a bag of leaf litter.

Detritus mass falling through fragmentation, leaching, catabolism, humification and mineralisation, faster or slower with conditions.

Make a litter bag lose 80% of its mass in one season; then set conditions where organic matter piles up instead.

Thinking lignin-rich detritus decomposes fast, that leaching makes nutrients available, or that humus decomposes quickly.

• Decomposers break complex organic matter down into inorganic substances such as carbon dioxide, water and nutrients. This is decomposition.
• The earthworm is called the farmer's friend because it helps break down organic matter and loosens the soil.
• Detritus, the raw material, is made of dead plant remains (leaves, bark, flowers) and dead animal remains, including fecal matter.
• Fragmentation: detritivores such as the earthworm break detritus into smaller particles.
• Leaching: water-soluble inorganic nutrients move down into the soil horizon and are precipitated as unavailable salts.
• Catabolism: enzymes of bacteria and fungi break detritus down to simpler inorganic compounds. These three steps run at the same time on the detritus.
• Humification forms humus, a dark, amorphous substance that resists microbes and decomposes very slowly. Being colloidal, it acts as a nutrient reservoir.
• Mineralisation: some microbes degrade the humus further and release inorganic nutrients.
• Decomposition mostly needs oxygen. It is slower when detritus is rich in lignin and chitin, and faster when it is rich in nitrogen and water-soluble substances such as sugars.
• Of the climatic factors, temperature and soil moisture matter most, acting through soil microbes. Warm, moist conditions speed it up; low temperature and anaerobiosis slow it, so organic matter builds up.

Teaching this idea? Put the simulation on your own page or LMS with this code.