Agriculture Reference
In-Depth Information
Chapter 2
R
ESPONSES OF
S
OIL
M
ICROBIAL
C
OMMUNITIES TO
C
LIMATIC AND
H
UMAN
I
MPACTS IN
M
EDITERRANEAN
R
EGIONS
Efimia M. Papatheodorou
1
Department of Ecology, School of Biology, Faculty of Sciences, Aristotle
University,U.P.Box 119, 54 124 Thessaloniki, Greece
A
BSTRACT
In Mediterranean regions climatic seasonality and exerted for millennia human
impacts such as grazing and deliberate fire drive the structure and function of ecosystems.
Recently, intensive agriculture, invasion of exotic species and atmospheric CO
2
enrichment are also involved. The function οf soil subsystem is important for ecosystem
maintenance providing nutrients released through microbially mediated decomposition.
Specifically in shallow and nutrient-limited Mediterranean soils, the contribution of soil
microbial communities to decomposition is even more important.
The aim of this paper is to examine the effect of climatic and human impacts on
characteristics of the soil microbial communities; biomass, composition and activity.
Estimates of biomass based on immobilized C and N, total PLFA or counts of bacteria
and fungi. For describing structural diversity PLFA and FAME results are used, while for
functional diversity BIOLOG data are considered. Results provided by molecular
techniques support our discussion of genetic diversity. Finally, data on respiration and
enzyme activities are used to assess microbial activity.
The survey shows that vegetation type exerts an influence on soil microbial features.
However, in comparison with seasonality the effects of plant species are of lower
importance. Grazing, by affecting vegetation patterning and soil compactness, is expected
to exert a great influence on soil microbial characteristics. Nevertheless, when seasonality
and grazing are compared variations due to season are greater than those induced by
grazing. Similar results emerge when seasonality is compared with agricultural practices.
The available information concerning the effect of fire and species' invasion on microbial
communities is really sparse. Burning reduces microbial diversity and most enzyme
