SUMMARY

The impacts of elevated atmospheric CO2 concentration on decomposition processes are reviewed, with consideration given to both the direct and indirect effects which CO2 may exert on soil processes.

Present work indicates that elevated concentrations of CO2 affect litter decomposition through changes in litter quality.

In particular, elevated CO2 decreases litter N concentrations with a resulting increase in C/N and lignin/N ratios, leading to a slow down in litter decomposition rates.

Such observations are true for both leaf and root litters, and for laboratory as well as field incubations. CO2 treatment does not appear to exert any effect on litter decay rates when there are no measurable changes in leaf chemical composition.

Furthermore, it has been identified that elevated CO2 is unlikely to exert any direct effects on soil biological activity, and that only effects mediated via changes in plants are likely to occur.

Although there is currently debate about the effect which increased C inputs to soils resulting from elevated CO2 may have on the turnover rates of existing soil organic matter, the overall conclusion is that soil C stores are increasing, and will continue to increase, under higher CO2 concentrations.

INTRODUCTION

If accurate predictions of the influence of elevated CO2 on terrestrial carbon (C) balance and on the global C cycle are to be made, then more information is needed about the development of above- and below-ground C stores under different atmospheric CO2 concentrations. The extent to which terrestrial ecosystems are able to ‘buffer’ against rising atmospheric CO2 concentrations by storing more or less C needs to be assessed, together with the changes which are currently occurring.