Introduction

The continued threat to the world's natural resources is exacerbated by the need to feed more than six billion people mostly through unsustainable farming practices. Till today very little efforts have been devoted to exploring and characterizing the significance of belowground biodiversity, as most studies were related to aboveground components (Wardle 2002; Bardgett 2005). Both aboveground and belowground components of terrestrial ecosystems are closely related, with soil organisms being intimately linked to plant communities (Bardgett 2005). Indeed, plants provide a source of C and other nutrients for the soil decomposer community in the form of plant litter and root exudates and, in turn, the soil biota, particularly its microbiota, decomposes soil organic matter, stabilizes soil structure and, through its essential role in the cycling of elements, releases nutrients for plant growth (Porazinska et al. 2003). In addition, although abiotic factors have traditionally been interpreted as the engineers of the vegetation patterns observed in terrestrial ecosystems, more recently, biotic interactions in the soil have also been reported as major drivers of the composition of plant communities (Hooper et al. 2000; Wardle and Zackrisson 2005). Therefore, in order to understand the complex patterns of biodiversity in soil ecosystem and, above all, their relationship to ecosystem function, a combined aboveground-belowground approach is required.

There is growing concern about biodiversity conservation and its role in maintaining functional biosphere. A large number of experimental evidence has concluded that most organisms are functionally redundant and that the functional characteristics of component species are at least as important as the number of species for maintaining essential processes (Bardgett and Shine 1999; Andren and Balandreau 1999). As per "insurance hypothesis," some minimum number of species is essential for ecosystem functioning under steady conditions and that a large number of species is probably essential for maintaining stable processes in changing environments (Loreau et al. 2001). However, theories on terrestrial ecosystems have been developed from aboveground observations, whereas comparatively few studies have been made in soil (Griffiths et al. 2000; Ohtonen et al. 1997; Wardle and Giller 1996). The links between aboveground and belowground ecosystem have not been studied in details and so poorly understood. Hence biodiversity and soil functioning are therefore explainable in a limited manner.

Loss of biodiversity due to intensive agriculture has fuelled the debate over the sustainability of current farming practices. Initially within Europe these fears have crystallized and then it has spread globally. A growing number of studies show that organic farming leads to higher quality soil and more biological activity than conventional farming, although the conclusion is not unanimous.

In this brief review the relationship between microbial diversity and soil functionality is discussed in the context of organic and conventional farming. To provide comprehensive view of the complex relations between microbial diversity and soil functionality under organic and conventional management practices, we consider: (1) the functional diversity of microbes under organic and conventional management; (2) quantitative and qualitative differences in soil functions; (3) molecular tool to measure microbial diversity and related limitations; and (4) functional changes during conversion to organic agriculture.

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Organic Gardeners Composting

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