An overview of the diversity of microorganisms involved in decomposition in soils

Abstract

Decomposition is a complex and prolonged process initiated before death and with rate constants varying with the nature of the substrate, and the characteristics of the environment. The process of decomposition is generally slow but presents a pattern suggesting sequential colonisation of senescent and dead tissue, associating weak parasites with senescing tissues and a primary and secondary saprophytic flora with the utilisation of simple carbohydrates and eventually of cellulose and lignin. A corpus of dead tissue is gradually broken down by the activities of the saprophytic soil fauna and the heterotrophic soil fungi, actinomycetes and bacteria. Among these, fungi are typically the pioneer colonisers and decomposers of dead tissues. Fungi are fitted for this pioneering role by their physical organisation into a network of mycelium which penetrate cellulose walls in plant tissue, even those strengthened by lignification, by a combination of enzyme action and growth pressure exerted by the hyphal apices, supported by rigid mycelium. The final results of this breakdown are the liberation of the essential mineral nutrients locked up in the dead organic matter, and yet needed by higher plants. Studies in the temperate region have shown that many of the practices involved in agricultural management decreases soil biodiversity and alters the structure of soil biological communities. In Kenya, very little work related to soil microbial diversity and decomposition as a process has been done. Research in soil science has focussed on fertility in relation to addition of organic and chemical fertilisers to the soil and the eventual crop yield, ignoring the effects of these additions to the soil inhabitants. There is a need, in Kenya and in other tropical countries, to focus more research on the gradual changes in diversity at finer levels of taxonomic resolution, and relating these changes to effects on ecosystem function as agriculture intensifies.