Soil functions and diversity

Saha S (2009) Soil functions and diversity in organic and conventional farming. A review. In Lichtouse E (ed) Sustainable agriculture reviews, vol 3. Springer, pp 41-76. In press. This volume... 

Soil Functions and Diversity in Organic and Conventional Farming... 

Fig. 10.1 Model representing components of soil ecosystem processes (Modified from Chapin et al. 1997). It depicts biotic control over the functioning of soil ecosystem. Biotic introductions, land use and atmospheric compositions influences species composition and diversity, which controls the biotic functional traits and ecosystem processes... 

The links between microbial diversity and soil functioning are unknown because it is difficult to measure microbial diversity. In addition, we generally measure soil functions by determining the rates of microbial processes, without knowing the microbial species effectively involved in the measured process (Nannipieri et al. 2003). The central problem of the link between microbial diversity and soil function is to understand the relations between genetic diversity and community structure and between community structure and function. 

Table 10.2 Summary of the effects of organic farming vis-a-vis conventional farming on different microbial diversity and soil functions... 

The relation between microbial diversity and soil functions is poorly understood because we cannot measure easily the microbial diversity, even if we can detect unculturable microorganisms by molecular techniques (Nannipieri et al. 2003). In addition, the present assays for measuring microbial functions determine the overall rate of entire metabolic processes, such as respiration, or specific enzyme activities, without identifying the active microbial species involved. The recent advances in RNA extraction from soil might permit us to determine active species in soil (Griffiths et al. 2000 Hurt et al. 2001). Further advances in understanding require us to determine the composition of microbial communities and microbial functions in microhabitats. 

Nannipieri P, Ascher J, Ceccherini MT, Landi L, Pietramellara G, Renella G (2003) Microbial diversity and soil functions. Eur J Soil Sci 54 655-670... 

Postma J, Schilder MT, Bloem J, van Leeuwen-Haagsma WK (2008) Soil suppressiveness and functional diversity of the soil microflora in organic farming systems. Soil Biol Biochem 40 2394-2406... 

Ros M, Klammer S, Knapp B, Aichberger K, Insam H (2006) Long term effects of compost amendment of soil on functional and structural diversity and microbial activity. Soil Use Manage 22 29-218... 

Bacteria inhabit every environment on the planet earth. They can be found in temperate as well as tropical areas, in deserts, ice caps, alkali lakes, oceans and hot springs. In one gram of soil, approximately 108 bacteria are present11 and these are estimated to represent over 10000 species. It is estimated that 50% of the biomass on this planet is microbial. Microorganisms represent by far the richest repertoire of functionally and chemically diverse producers of secondary metabolites in nature. 

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