The core theme addressed by members of the SIMBIOS Centre has direct relevance to a number of environmental issues, in particular (but not exclusively) global climate change, the possibility to decrease the amount of CO2 released in the atmosphere by carbon sequestration in soils, or the remediation of contaminated subsurface environments.Soils could potentially speed up global climate change. Globally, in the surface meter alone, world soils contain over 1550 Pg of carbon, i.e., about 300 times the amount of carbon now released annually through the burning of fossil fuels. With globally 68 to 120 Pg C annually, soil respiration represents the second largest carbon flux between ecosystems and the atmosphere. This is more than 10 times the current rate of carbon release from fossil-fuel combustion. Each year, approximately 10% of the atmospheres CO2 is cycling through the soil. Thus, even a small change in soil respiration could significantly intensify or mitigate current atmospheric increases of CO2, with potential feedbacks to climate change. It could also affect markedly the metabolism of soil-borne nitrogen, and the release to the atmosphere of large quantities of nitrogen oxides. Despite the global significance of these processes as well as a considerable scientific commitment to its study over the last decades, understanding of the effect of environmental factors on the dynamics of carbon and nitrogen in soils is still lacking in many respects, particularly in relation with the consequences of possible temperature rises and changes in precipitation patterns in years to come.
One of the strategies often proposed to help mitigate some of the observed global climate change involves the sequestration of carbon in soils. But, on the other hand, quite a few priming experiments, in which fresh organic matter or easily degradable organic compounds are added to soils, have resulted in the degradation of the young organic matter, but also in old, presumably recalcitrant, organic matter getting degraded rapidly. Therefore, it is unclear under what conditions active strategies currently proposed to increase the organic matter content of soils would be effective. It seems clear that to make progress in this area, it would be necessary to first understand why some fractions of the organic matter present in a soil are not degraded under normal conditions (in the absence of priming). In many cases, this may have to do with the geometry of the interstitial space in soils, and the accessibility of the organic matter.
The same may apply to other chemical compounds in soils as well. It is unclear at this point what controls the availability of many organic contaminants in subsurface environments. Ten years ago, the dominant belief among specialists was that xenobiotics that had aged in a soil or aquifer material for a long period of time, were sequestered, largely unavailable, and therefore non-toxic. However, since then, as with the recalcitrant organic matter in priming experiments, evidence has shown that non-bioavailable organic xenobiotics could easily become available if other compounds were added to the system, or after adaptation of the local microflora. Again, there is a strong suggestion in this case that the spatial heterogeneity of the matrix in which these xenobiotics are located may cause some of the observed results.
Baveye, P. 2007. Soils and runaway climate change. Journal of Soil and Water Conservation. 62(6):139A-143A.