Decomposition

Decomposition

The breakdown of organic matter into simpler inorganic compounds

Decomposition is essential for …

Nutrient cycling, soil fertility, and energy flow

Decomposition converts …

Detritus to carbon dioxide, water, and mineral nutrients

Key players of composition:

Microorganisms, detritivores, scavengers

Types of detritivores

Microfauna, mesofauna, macrofauna, megafauna

Microfauna

Less than 0.1 mm. Includes bacteria, fungi, and protozoa.

Mesofauna

Between 0.1 to 2.0 mm. Includes mites and springtails.

Macrofauna

Between 2 to 20 mm. Includes nematodes and fly larvae.

Megafauna

Over 20 mm. Includes earthworms, snails, and millipedes.

Role of Microfauna

Enzymatic breakdown or organic molecules

Roles of Mesofauna

Shred litter, increases surface are3a for microbes. Important in soil structure

Roles of Macrofauna

Fragments litter, mix soil

Roles of Megafauna

Ingest and mix soil. Enhance soil aeration.

Affect rates of decomposition

Temperature, moisture, oxygen availability, chemical quality, biotic community

Warmer temperatures…

cause faster decomposition

Colder temperatures …

Cause slower decomposition (slower microbial activity)

Moist conditions …

Favor microbes

If moisture is too dry, …

Dormancy occurs

Very wet conditions

Aerobic (oxygen available) causes …

Rapid decomposition

Anaerobic (no oxygen available) causes …

Slow, partial decay (ex: peat bog).

Chemical quality - simple sugar, amino acids

Decompose quickly

Chemical Quality - Lignin, cellulose, waxes, tannins

Decompose slowly

Biotic Community - Rich soil fauna, microbial diversity

Faster decomposition

Biotic Community - Disturbed, polluted soil

Slower decay

Tropical rainforest - rate of decomposition and why

Very fast; warm, moist, high microbial activity

Temperate forest - rate of decomposition and why

Moderate; cooler seasons slow decomposition

Grasslands - rate of decomposition and why

Moderate to fast; High root turnover, moderate moisture

Boreal forest/Tundra - rate of decomposition and why

Very slow; cold, acidic soils, permafrost

Wetlands - rate of decomposition and why

Slow; anaerobic conditions

Decomposition process

Sequence of physical and biological processes. Transform organic matter into organic nutrients.

Decomposition steps:

Leaching, Fragmentation, Chemical Alteration (Catabolism), Mineralization, Humification

Leaching

Soluble compounds dissolved ad washed out of litter by water

Leaching Examples

Amino acids, salt, sugar

Leaching Importance

Happens early in the process, removes easily soluble nutrients, makes litter lighter and nutrient poorer.

Leaching Speed

Fastest in wet, rainy environments (tropical forests)

Fragmentation

Physical breaking down of litter into smaller pieces

Who does fragmentation?

Earthworms, termites, millipedes, beetles

Fragmentation Importance

Increase surface area for microbes, mixes organic matter into the soil (bioturbation).

Chemical Alteration

Microbes use enzymes to break down complex materials

Who does Chemical Alteration?

Bacteria, fungi

Chemical Alteration Targeted Molecules

Cellulose, starch, proteins, lipids, lignin

Mineralization

Conversion of organic nutrients into organic forms useable by plants, converting Nitrogen into Nitrate.

Mineralization Process

Microbial respiration and enzyme activity release CO2, water, and minerals

Mineralization Importance

Returns nutrients to the soil for reuse by primary producers

Humification

Formation of Humus

Humification Importance

Improves soil structure, improves water retention, stores Carbon long-term.

Decomposition Pathway

Dead organic matter, leaching, fragmentation, microbial breakdown, mineralization, Humification

Importance of Recyclers

Decomposes recycle nutrients back into the ecosystem, most nutrients (C, N, P) are used and reused multiple times within a system.

Without decomposes …

Nutrients would remain locked in dead organic matter, ecosystems would run out of usable nutrients

Importance of Decomposition

Reduce loss of nutrients and energy, decomposes get eaten by predators

Reduce loss of nutrients and energy

Decomposes are part of the detrital food chain, provide food for higher food levels.

Decomposers get eaten by predators

Retains nutrients and energy in the system, Herbivores and predators feeding on decomposers close the loop in energy transfer

Warm moist conditions in tropical rainforests

Rapid decomposition, nutrients quickly recycled and taken back up by plants, soil nutrient poor (little nutrients stay in the soil and most cycles up through biomass of trees)

Decomposition Aquatic Systems

Decomposition occurs in sediment; regenerates nutrients for algae and phytoplankton, drives primary productivity in lakes and oceans

Decomposes communities are …

Less studied ompared to plants and animals. Many species are microscopic or cryptic, hard to study and identify.

Which of the following have a fast decomposition rate?

Leaves with a high concentration of Proteins