Agriculture Reference
In-Depth Information
T
HE
E
FFECTS OF
C
LIMATE
C
HANGES AND
C
O
2
E
NRICHMENT
There is a rather wide concensus within the scientific community regarding the climatic
consequences of doubling CO
2
concentrations in the atmosphere and the potential negative
impacts of climate changes on natural and human made systems. These impacts will
exacerbate many of the existing problems (e.g. desertification, water loss etc) especially along
the southern and eastern perimeters of the Mediterranean region (Giupponi and Shechter
2003). Changes in precipitation patterns and temperature regimes could introduce new threats
to natural ecosystems. For Mediterranean areas, most models predict temperature increase
and greater inter and intra-annual variability in rainfall distribution.
Few studies undertaken within the DEGREE project (Diversity Effects in Grasslands
Ecosystems of Europe) examined the effects of climate changes on soil processes and
diversity in European grasslands. Since the rest experimental sites are not identified as
Mediterranean areas, data presented herewith concern only the soil function in a Greek
grassland (Papatheodorou et al. 2004a). Soil temperature and humidity were artificially
manipulated in the field in accordance to a climate change scenario proposed by Palutikof et
al. (1996). According to this scenario, smoother temperature variations and more regular
distribution of precipitation in time were predicted. The artificial modifications resulted in
damped temperature fluctuations and in drier soil conditions. Due to their narrow range, these
changes were considered as small-scale compared with large-scale ones. As large-scale
changes were considered the seasonal fluctuations of climatic variables.
The size of microbial biomass was not affected by small-scale variations but activity did.
This was related to the regular distribution of rainfall that induced episodes of enhanced
activity during the drought period. All microbial parameters showed a significant response to
large-scale variations, indicating that seasonal variations in temperature and humidity were
more important than small-scale changes described by climate change scenarios. The
functional diversity of GN bacteria together with evennenss and richness responded mainly to
large-scale variations of temperature and humidity, reflecting seasonal differences in the
functioning of the soil bacterial community (Papatheodorou et al. 2004b). The components of
catabolic diversity decreased from summer to winter. Since loss in evenness relates to
unstable or less resilient microbial function (Degens et al. 2001), a perturbation in winter can
induce more dramatic changes in microbial community structure and function compared to
changes caused by a summer disturbance.
The above studies concluded that small-scale variations in climatic variables had no
significant effect on various aspects of soil microbial community. However, as Balser et al.
(2002) mentioned the general idea of a rapid equilibrium of soil microbial communities with
changing climate needs an exhaustive investigation. This is also supported by Balser and
Firestone (2005) who examined the response of microbial composition to changing climatic
factors by a transplanting experiment. They found that composition remained constant even
after 2 yrs of exposure to new conditions.
The effects of drought on the microbial community structure involved in litter
decomposition and specifically in Mediterranean pine needles' degradation were studied by
Wilkinson et al. (2002). The microbial community colonizing litter during the initial stages of
decomposition could be highly variable even between adjacent pine needles. This is due to
biotic interactions e.g. grazing effects (Maraun et al. 1998) and to microclimatic conditions of
