Terrestrial Palaeoecology and Global Change

224 Valentin A. Krassilov. Terrestrial Palaeoecology
rates by ectomycorrhizal symbionts in turn affecting growth rates and carbon allocation
in the forest trees (Fransson et al., 2001; Oren et al., 2001). At an elevated atmospheric
CO 2
level, an increase in the soil carbon concentration is accompanied by a rise of
cellulose decomposers among the soil fungi, as well as collembolans and other fungivorous
arthropods (Jones et al., 1998). Generally, an elevated CO 2
uptake by vegetation
correlates positively with the biological diversity (Naeem et al., 1994) and is considered
as a factor of the latter.
Temperature – CO 2
– temperature system. As it follows from the above discussion,
atmospheric CO 2
fluctuations, both recent and over geological times, depend on the
dynamic interactions of the lithospheric, hydrospheric and biotic reservoirs and a balance
of the (mostly not as yet quantified) positive and negative feedbacks. Tapping any of the
major reservoirs, be it by a magmatic–metamorphic outgassing, spread of warm surface
waters, deforestation, degradation of soil, burning of fossil fuel or biomass, leads to carbon
reallocations with potential climatic effects.
However, the present-day technogenic “experiment” shows that even a massive
emission of greenhouse gases is rapidly compensated for, as about three times less CO 2
resides than is emitted. The existing models of greenhouse-generating CO 2
emissions
assumes a linear response of CO 2
-regulating systems, ignoring autocyclicity, an inevitable
outcome of regulation with negative feedbacks, as well as a possibility of overcompensation.
The latter arises due to the inertia of negative feedbacks. Overcompensation
potentially occurs in the CO 2
– silicate weathering, CO 2
– carbonate deposition and CO 2
– glaciation systems (above), each of which may cause a reversion of the climate trend.
The CO 2
-centered models of climate change are inadequate not because of an imprecision
of the basic estimates, a deficiency surmountable with accumulation of data
and sophistication of techniques, but rather because of a reductionist approach to the
immensely complicated system that does not come to any simplistic expectations. A
prediction (of a rapid doubling the atmospheric CO 2
) based on an extrapolation of the
recent technogenic emission rates would inevitably fail on account of the negative feedbacks
that, with elevation of pCO 2,
would alter not only the rates but possibly the direction
of the process as well. Eventually the process would come under control of natural
regulation.
Thus, over the warming trend, more CO 2
is spent on chemical weathering of silicate
minerals and is deposited with carbonates to be returned to the atmosphere with their
dissolution or thermic decomposition. In this geochemical circuit, the relative rates of
CO 2
consumption and release depend on the air temperature that affects the weathering
rates both directly, as an enhancer of chemical reactions, and indirectly, through its effects
on mycorrhiza (Smith & Read, 1997), decomposition of organic matter and related
rhizospheric processes (reviewed in Boucot & Grey, 2001). Air temperature and the
related SST are engaged in regulation of carbonate deposition (lysocline fluctuations
relative to thermocline). The geochemical cycle thus falls under control of the temperature
cycles induced by the factors (orbital, tectonic, eustatic, etc) other than CO 2
.