Peatland and mineral soils are important reservoirs in the global carbon cycle and there is much interest in characterising the response of their carbon stores to temperature perturbations. Peatlands are notable also because of their dual function as carbon capacitors and amplifiers in the Earth System, sequestering CO2 into soil biomass, but also producing CH4, a more potent greenhouse gas. Cycling of H2 in soil is poorly characterised despite accounting for 80% of the annual atmospheric H2 sink. This study adapted a novel heating and cooling instrument, typically used for process chemistry, as a new form of soil incubator. Its ability to generate cyclical and ramped temperature regimes was exploited to simulate diurnal soil temperature variations while concentrations of CH4, CO2 and H2 were measured. These data were used to calculate turnover rates, F-ratios, Q10 factors, activation energy and Gibbs free energy for specific microbial and enzymatic processes. Determinations were compared to data from conventional stepped temperature incubations presently used in models. Lower rates of methanogenesis occurred in cyclical versus constant temperature incubations; however, the effect existed only in high trophic status peat. Temperature sensitivity of anaerobic CO2 production also was linked positively to nutrient status. Rates of H2 production were unaffected by temperature regime but were highly sensitive to temperature. Rates of aerobic CO2 production in mineral soil were more sensitive to temperature in organic matter rich soil while H2 cycling in the same soil occasionally exhibited unusual behaviour that suggested H2 (and possibly CH4) was produced in anoxic micro-sites. Methanogenesis functioned near its thermodynamic limit and F-ratios were consistently lower than values used in most peatland CH4 models. Living plants were excluded from these experiments and thus findings carry the caveat that a major source of labile carbon was absent. The importance of root biomass to carbon mineralization processes was established during characterisation of in situ conditions at the sites from which peat was obtained for the incubations.
|Date of Award||2008|
- The University of Bristol
|Supervisor||Edward Hornibrook (Supervisor)|