Soil particles offer protection for carbon reservoir
Increasing carbon dioxide (CO2) levels in rapidly growing poplar forests has been shown to cause elevated carbon sequestration in the tree itself. Logically, there should also be more carbon available in roots and the surrounding rhizosphere. Increased microbial activity in the carbon cycle may mean an increase in soil organic matter (SOM) aggregation and a consequently stabilised carbon pool. Whether or not this is the case is dependent on the type of forest according to previous research. Trials were conducted by the European project EUROFACE at a EUROFLUX site. EUROFLUX is an EU funded project to monitor the water vapour and CO2 fluxes of European forest. First, they investigated how carbon cycle dynamics and SOM pools were affected by afforestation when a wheat crop was changed to a poplar forest. Secondly, poplar stands were compared when exposed to FACE (Free air CO2 enrichment). Afforestation increased stable carbon pools which suggested that sequestration may be promoted in these cropped soils. However, afforestation did not promote soil particle formation as predicted. Elevated CO2 levels however did encourage aggregation. By contrast, FACE soils showed an overall decrease in carbon due to an increase in organic matter decomposition. In soils supporting fast growing poplar species, FACE promoted the stabilisation of the C in microaggregates due to physical protection by larger soil particles, macroaggregates. The data compiled as a result of this research underlines the complexities of the processes involved. Soil dynamics would appear to be a very significant factor in the fate of carbon under conditions where levels of carbon dioxide are rising.
