Mechanisms of organic matter stabilization and destabilization in soils and sediments: conference introduction

Abstract

The interest in organic matter continues to gain momentum, mainly through the ongoing concern about increased levels of atmospheric greenhouse gasses (GHG). Since soils contain approximately one-third of the carbon known to exist in all fossil fuel reserves (Scharpenseel and Becker-Heidmann 1990), its potential to act as a sink or source of atmospheric GHGs is of great interest. Changes in soil management, particularly the adoption of lowor no-till systems, can result in increased soil C levels and hence represent a sink for atmospheric C. Increasing soil C stores also improves soil fertility and productivity and so provides a clear win-win situation. On the other hand, the degradation of the world’s soils through erosion, salinization, acidification and desertification, which continues apace, generally results in a net release of C to the atmosphere, and is just as clearly a lose-lose situation. However, the biggest concern is that global warming itself will increase rates of organic matter degradation, resulting in a positive feedback loop, where warming releases soil C to the atmosphere, which in turn causes further warming. Coastal and oceanic sediments also contain substantial organic C stores with annual burial rates estimated to be in the order of 130 Mt (Summons 1993). In order to be able to predict how these C stores will be affected by changes in either climate or management, we need a detailed understanding of C cycling in soils and sediments. Although the basics are well known— most C added to soils and sediments comes either directly or indirectly from photosynthesis in the form of plant and microbial biomass, and most C is lost through microbial decomposition—the fact that substantial stores of non-living organic C exist in soils and sediments is evidence that considerable time can pass between the death of an organism and respiration of its biomass to CO2. During this time, C is removed from the atmosphere. We clearly need to understand the mechanisms by which this organic matter is stabilized against decomposition and the mechanisms by which it can be destabilized and made available for decomposition, if we ever hope to be able to predict changes in, and perhaps even control, these C stores. This special issue of Biogeochemistry presents some of the results from the Third International Conference on Mechanisms of Organic Matter Stabilization and Destabilization in Soils and Sediments (SOM3), which took place on 23–26 September 2007 at Glenelg, near Adelaide, Australia. As the third conference in what is now recognized as a series of biennial or triennial conferences, it was the first to R. Smernik (&) Soil and Land Systems, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia e-mail: Ronald.smernik@adelaide.edu.au