Litter decomposition is defined as the process through which dead organic material is broken down into particles of progressively smaller size, until the structure can no longer be recognized, and organic molecules are mineralized to their prime constituents: H2O, CO2 and mineral components.
Main aim of litter decomposition study is to:
1. quantify rates of litter decay
2. develop mathematical models that better represent decay dynamics
3. identify litter quality factors that control decay rates, and eventually the equation defining the relationship
4. determine dynamics of nutrients and carbon-based compounds during litter decay
5. identify climatic factors that control decay, and eventually the equation defining the relationship
6. identify the interdependence between litter quality and climate
7. evaluate the role of soil organisms
The process of litter decomposition is of three main types:
(1) leaching of soluble compounds into the soil.
(2) fragmentation of litter into smaller sizes and
(3) catabolism by decomposer organisms (i.e. micro-organisms and fauna)
There are two groups of organisms that make use of dead organic matter (saprotrophs): decomposers (bacteria and fungi) and detritivores (animal consumers of dead matter).
Regulation of Decomposition:
Decomposition is regulated by factors like:
During decomposition the chemical composition of litter changes due to selective degradation of soluble and structural compounds, to the in-growth of fungal and bacterial cells within the litter and to the transfer, in and out of the litter, of mineral nutrients.
Overall, with progressing litter decay, structural compounds accumulate, while soluble nutrients may initially be leached and, subsequently, either immobilized or mineralized depending on microbial demand (Berg and Staaf, 1981).
The decomposability of litter decreases with time. Rates of leaf litter decay are controlled by climate: faster rates are measured under warmer and wetter conditions. Despite this being an obvious statement, it is still debated which climatic index best predicts decay rates. On the basis that temperature increase would speed up decomposition as long as there is water available in the soil, actual evapotranspiration (AET) has been proposed as the climatic index that – because AET also increases with temperature when there is water available for evaporation (Rosenberg et al., 1983)
Two of the major organic components of dead leaves and wood are cellulose and lignin. These pose considerable digestive problems for animal consumers, most of which are not capable of manufacturing the enzymatic machinery to deal with them. Cellulose catabolism (cellulolysis) requires cellulase enzymes. Without these, detritivores are unable to digest the cellulose component of detritus and so cannot derive from it either energy to do work or the simpler chemical modules to use in their own tissue synthesis. Cellulases of animal origin have been definitely identified in remarkably few species, including a cockroach and some higher termites.
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