Index >> Fundamentals of Microbial Ecology >> Types of Succession

Allogenic succession This occurs when a habitat is altered by environmental factors (seasonal changes), for example, when a salt marsh develops from a tidal mud rich in detritus. Pioneer organisms will be dominated by salt-loving organisms like some algae which will grow and add organic nutrients to the marsh followed by nitrogen fixing algae. Once primary succession is in place, it may be stable for decades. Ultimately coastal marshes can be converted completely into terrestrial communities.

Substrate succession This can be explained with the example of microbes involved in the development of structured soils from bare rock surfaces. The low level of soluble minerals, absence of organic matter and extremes of temperature and moisture on the rocks makes it almost uninhabited and remain a virgin environment. The pioneer organisms could be only the tolerant algae and cyanobacteria with mucilaginous walls or slime capsule and which can fix nitrogen (e.g. Porphyrosiphon notarisu, Gloeocapsa spp., Gloecocystis spp., Nostoc muscorum).

In soils which have the organic matter in the form of plant litter and animal bodies (soil arthropods) and which arrive with a resident microflora in them, substrate succession usually starts off with the breaking of dormancy of spores affected by the organic matter.

There is a great increase in the zymogenous population (Mucor, Rhizopus). Among the bacteria are Bacillus and Pseudomonas spp. These microorganisms have very high competitive saprophytic ability. As the easily utilisablesubstrates are consumed and the pH drops due to immobilisation of cations, population slowly changes to ascomycetes, actinomycetes and protozoans which lyse and degrade the fungal hyphae which was a part of initial invasion of substrate. The final stage in the succession is the invasion of the much depleted substrate by autochthonous organisms especially those degrading lignin.