Soil Carbon

Across the planet, soils store about twice as much carbon as the atmosphere, making soils a large and important reservoir of carbon. However, carbon cycling in soils (the routes by which carbon enters the soil, is modified by physical, chemical and biological processes, and ultimately leaves the soil through microbial respiration or leaching) is not well understood. There is particular interest in understanding the soil carbon cycle, since we need to be able to predict what will happen to soil carbon as climate changes due to global warming.

Carbon cycling in soils is biologically driven by bacteria, fungi and invertebrates, as they act upon plant litter-derived carbon (above ground), root deposition and soil organic matter (below ground). The impact of these organisms on carbon cycling depends upon biological community structure and activity. We determine invertebrate and microbial community structure by extracting the organisms, or biochemical markers of the organisms, from the soil. This is done using techniques such as dry and wet extraction for invertebrates, traditional microbiological methods such as plate counts and respiration measurement, and chemical and molecular methods such as phospholipid fatty acid (PLFA) analysis and DNA/RNA based analysis.

Amongst other methods, we measure biological activities by determining microbial respiration rates, especially rates of release or consumption of the trace gases carbon dioxide, methane and nitrous oxide. We have a mobile laboratory that can measure emitted soil gases directly and can also store gases for more detailed laboratory analysis, e.g. stable isotopic composition.

One of our research tools is the use of stable isotopic methods, in which the 13C content of soils, trace gases, individual soil-derived compounds and dissolved organic carbon (DOC) are measured. The 13C content of a material gives us information on the its source and the underlying soil processes. We work closely with the NERC Stable Isotope Facility (Lancaster Node) to perform these analyses.

A great deal of our work is performed in the field, especially at sites such as Moor House and Plynlimon, although in the past few years we have worked at over 30 different sites.

See also: Soil Biodiversity and Ecosystem Function.