Geoscience Reference
In-Depth Information
elevations, by chytridiomycota. As seen in the case of
Atelopus
harlequin frogs, the spread of soil pathogens due to climatic
changes can significantly affect life at the macroscale and ulti-
mately lead to species extinction Briones et al. (2004).
Indirect
climate-
microbe
feedbacks
Climate change can also have marked indirect effects on soil
microbial communities and their activity—and hence the
potential for microbial feedback to climate change—through
its influence on plant growth and vegetation composition.
Such plant-mediated indirect effects of climate change on soil
microbes operate through a variety of mechanisms, with dif-
fering routes of feedback to climate change, but these can be
broadly separated into two. The first mechanism concerns the
indirect effects of rising atmospheric concentrations of carbon
dioxide on soil microbes, through increased plant photosyn-
thesis and transfer of photosynthate carbon to fine roots and
mycorrhizal fungi (Johnson et al., 2005; Högberg and Read,
2006; Keel et al., 2006) and heterotrophic microbes (Zak
et al., 1993; Bardgett et al., 2005). It is well established that
elevated carbon dioxide increases plant photosynthesis and
growth, especially under nutrient-rich conditions (Curtis and
Wang 1998) and this in turn increases the flux of carbon to
roots, their symbionts and heterotrophic microbes through
root exudation of easily degradable sugars, organic acids and
amino acids (Díaz et al., 1993; Zak et al., 1993). The con-
sequences of an increased carbon flux from roots to soil for
microbial communities and carbon exchange are difficult to
predict, because they will vary substantially with factors such
as plant identity, soil-food-web interactions, soil fertility and
a range of other ecosystem properties (Wardle 2002; Bardgett,
2005). But some potential outcomes for soil microbes and car-
bon exchange include increases in soil carbon loss by respira-
tion and in drainage waters as dissolved organic carbon due
to the stimulation of microbial abundance and activity, and
enhanced mineralisation of recent and old soil organic carbon
(Zak et al., 1993).
Future
perspectives and
wrapping up
An understanding of soil microbial ecology is central to our
ability to assess terrestrial carbon cycle-climate feedbacks.
However, the complexity of the soil microbial community and
its many roles, coupled with the myriad ways that climate and
other global changes can affect soil microbes, hampers our abil-
ity to draw firm conclusions on this topic. Despite this uncer-
tainty, we argue that progress can be made in understanding the
potential negative and positive contributions of soil microbes