Ecosystem Decomposition

BIOLOGY ECOSYSTEM DECOMPOSITION DECOMPOSITION :  Decomposition (Formation of Humas) : Decomposers break down comlex organic matter into inorganic substance like carbon dioxide, water and nutrients and the process is called decomposition. Dead plant remains such as leaves, bark, flower and dead remains of animals, including fecal matter, constitute detritus, which is the raw material for decomposition.  Detritus involves two types : (A) Above ground detritus : (Plant litter, dead plant parts & animal parts excretory substances). (B) Below ground detritus : Dead roots of plant, Dead animals in soil. The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation. Humification Humus Detritus Environmental Conditions Fragmentation, Leaching, Catabolism Mineralisation CO2, H2O Nutrients Fig: Processes involved in decomposition of detritus 1 BIOLOGY  Detritivores (eg., earthworm) break down detritus into smaller particles. This process is called fragmentation. By the process of leaching, water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavilable salts. Bacterial and fungal enzymes degrade detritus into simple inorganic substance. This process is called as catabolism.  It is important to not that all the above steps in decomposition operate simultaneously on the detrius. Humification and mineralisation occur during decomposition in the soil. Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.  Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors. In a particular climatic condition, decomposition rate is slower if detrius is rich in lignin and chitin and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars.  Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes. Warm and moist environment favour decomposition where low temperature (< 10ºC) and an anaerobiosis inhibit decomposition resulting in build up of organic materials.  Decomposition requires years at very high altitude or lattitudes. Rate of decomposition is low in prolonged dry soil like in tropical desert.  The actual rate of decomposition depands on environmental conditions and detritus quality.  Nutrient Immobilisation - In the process of decomposition, some nutrients get tied up with the biomass of microbes and become temporarily unavailable to other organisms. Such incorporation of nutrients in living microbes (bacteria and fungi) is called nutrient immobilisation.  Nutrients gets immobilized for variable periods and gets mineralised later after the death of microbes. This immobilization prevents nutrients from being washout form the ecosystem.  Two types of Humus (i) Mor (Coarse terxtured humus)- It is raw humus and is formed in acidic soil (PH - 3.8 4.0) 2 BIOLOGY in which decomposition of litter is slow because it has less number of decomposer organism. (ii) Mull – This is completely decomposed litter. i.e., humus because rate of decomposition is fast due to high PH of soil. (Best PH of the soil 5.5 to 6.5) A tree grows in the soil Some are eaten by insects and other animals. Nutrients and energy enter food web. A green leaf falls to the ground Leaves partially consumed by decomposers such as fungi and bacteria. They begin to lose from and become litter. Some nutrients leach into soil by chemical action Further decomposition by earthworms, bacteria, soil, mites, fungi, etc. Organic rich soil 3