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Durham University

Department of Earth Sciences


Publication details for Professor Fred Worrall

Clay, G.D. & Worrall, F. (2015). Oxidative ratio (OR) of Southern African soils and vegetation: Updating the global OR estimate. CATENA 126: 126-133.

Author(s) from Durham


Oxidative ratio (OR) is the ratio of moles O2 released per mole CO2 sequestered through photosynthesis in the terrestrial biosphere. The lower the OR value the more CO2 an environment can potentially sequester. It is this property of the organic matter that plays a role in models of CO2 partitioning between the atmosphere and the biosphere. Recent studies have shown that the accepted value of OR (1.1 ± 0.05) may not be appropriate but that there are a number of research gaps before a full account of global OR values can be carried out.

This study aims to fill some of the research gaps by carrying out a targeted sampling campaign in southern Africa. Vegetation, litter and soil samples were taken from a range of soil orders and biomes across a series of locations in South Africa and Swaziland. From these samples this study has been able to update a recent meta-analysis and show that although there were significant differences between some sites and vegetation types, there was no significant difference between the soil orders or biomes sampled. This study has also been able to update the global ORterra estimate to 1.06 ± 0.06.