plant surface microbiology.pdf

4 Role of Functional Groups of Microorganisms on
the Rhizosphere Microcosm Dynamics
Galdino Andrade
1 Introduction
This chapter discusses the role of functional microorganism groups that live
in the rhizosphere and contribute to nutrient cycling. Soil ecology has much
to contribute to our knowledge of important processes at the ecosystem
level, such as how plant growth is affected by the rhizosphere biota, organic
matter dynamics and nutrient cycling, and soil structure dynamics (Brussaard
1998).
Many groups work directly on plant nutrition, such as rhizobia and mycorrhiza
fungi which are symbiotic. These groups have been studied extensively
in the last few decades, but little has been investigated about the relationship
between other functional groups, notwithstanding that many other interactions
exist in the rhizosphere that are ecologically important to maintain life
on Earth and consequently in the soil, since this is a part of the whole.
Many steps of nutrient cycling are made exclusively by microorganism
populations, and some of them may participate in one or more biogeochemical
cycles. The understanding of these interactions between different populations
according to specific phenotypes could give a better perspective about
the processes that are occurring. A percentage of the microbial community
can be grown in culture medium under laboratory conditions, if cultured
microorganisms are considered as a sample of microbial community in soil
microcosms. Grouping the microbial communities by phenotypes is more
realistic than determining the species that are involved in these process.
Although only a small amount of high quality data can be obtained, it is possible
to monitor the effects of hazardous chemical products, environmental
disturbance, and disturbances in nutrient cycling and soil fertility controlled
by these organisms, and also ecosystem health.
Functionality aspects are more important than biodiversity in natural or
sustainable agriculture systems. Some questions could be raised concerning
biodiversity. The first question that should be asked is: what is more important
to the Earth? The number of species that compose the functional group
Plant Surface Microbiology
A.Varma, L. Abbott, D. Werner, R. Hampp (Eds.)
© Springer-Verlag Berlin Heidelberg 2004