Soil Teeming with Life: New Frontiers for Soil Science - Sustainable Management of Soil Organic Matter - page 411

in atmospheric CO 2 have led to an alteration in the equilibrium between
soil organic matter and the pre-industrial CO 2 concentrations. This is
complicated further by the enrichment of our environment with fixed N,
which interacts with the added organic C in soils to produce effects on soil
properties and soil organisms that are difficult to anticipate (Swift et al .,
1998). Most of the carbon held in terrestrial ecosystems is in the soil
(~1500 10 15 g) and is derived from plant and animal material (Batjes,

1996). Changes in the soil carbon stores may result from the effects of
elevated CO 2 on plant growth and from the climate changes resulting from
the change in global atmospheric composition. Elevated levels of CO 2 can
affect the quality of leaf and fine root litter, their decomposition rates and
the relationship between litter quality and decomposition (Cotrufo et al .,
1998). Elevated levels of atmospheric CO 2 were shown by Torbert et al .to
increase both soil organic carbon and total nitrogen content under soybean
and sorghum. Martin-Olmdèo et al . found no direct plant-mediated effect
of elevated CO 2 on nitrous oxide production or emission from soil.
However, they considered that the positive effect on plant growth and
microbial biomass by the CO 2 might affect potential feedback effects
between soils and atmosphere.
The build-up of greenhouse gases can be limited quite considerably
through improved soil management; according to Smith et al . agricultural
soils can be particularly important. The sequestration of carbon in organic
matter in agricultural soils is an important mitigation option. This can be
achieved using organic amendments, improved residue management and
tillage techniques, alternative cropping regimes and changes in land use
cover. Afforestation and bioenergy production are the changes with the
greatest mitigation potential.
Soils of the boreal and sub-arctic vegetation zones are important for
carbon storage, particularly in the sub-soil. Guggenberger et al . stated that,
in Siberia, where global warming is relatively rapid, belts of vegetation may
shift northward enabling more soil organic matter to be stored, though
emissions of greenhouse gases may increase.
A future problem in many areas of the world will be an increasing
incidence of forest fires which leave soil exposed and vulnerable to
degradation. Haslam et al . showed how solid-state 13 C-nuclear magnetic
resonance spectroscopy can be used to estimate the changes in soil organic
matter quality as organic material reaccumulates after fires.

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Biodiversity

Organic matter sustains the life of soil and this is inherently important to
the concept of soil health. Microorganisms in particular play an essential
role in the transformations of organic matter and nutrients that underpin