Estimating the oxidative ratio of UK peats and agricultural soils

Organic matter in the terrestrial biosphere has a fundamental role in moderating the exchange of CO2 between the atmosphere and the biosphere. One important property of organic matter is its oxidative ratio (OR); that is, the ratio of moles O-2 released per mole CO2 sequestered through photosynthesis, that is, the lower the OR, less O-2 is released per mole of CO2 fixed. In global assessments of CO2 partitioning, the failure to account for changes in OR could lead to an underestimate of terrestrial carbon sequestration. It is known that OR can vary between environments and management, but what other factors could be playing a role in controlling OR? This study measured the OR of a range of peat (Histosols) and mineral soils (Inceptisols) under similar management from across the United Kingdom to investigate how OR varies within and between material types. The study shows that OR values varied significantly between material types (median peat OR=1.10, median vegetation OR=1.03 and median mineral soil OR=1.14), and they also varied between study sites. Furthermore, there were no significant differences in OR with peat depth. Given the results from this study, we can suggest that future sampling strategies should include sampling of the major carbon pools (i.e. vegetation, litter and soil) and that, as a first approximation, OR can be examined on the basis of these carbon pools alone. The values measured in the study give a new residence time-weighted global OR estimate for the terrestrial biosphere (ORterraglobal) of 1.056 +/- 0.02.