The speed of soil carbon throughput in an upland grassland is increased by liming

In situ C-13 pulse labelling was used to measure the temporal and spatial carbon flow through an upland grassland. The label was delivered as C-13-CO2 to vegetation in three replicate plots in each of two treatments: control and lime addition. Harvests occurred over a two month period and samples were taken along transects away from the label delivery area. The C-13 concentration of shoot, root, bulk soil, and soil-respired CO2 was measured. There was no difference in the biomass and C-13 concentration of shoot and root material for the control and lime treatments meaning that the amount of C-13-CO2 assimilated by the vegetation and translocated below ground was the same in both treatments. The C-13 concentration of the bulk soil was lower in the lime treatment than in the control and, conversely, the C-13 concentration of the soil-respired CO2 was higher in the lime. Unlike the difference in bulk soil C-13 concentration between treatments, the difference in the C-13 concentration of the soil-respired CO2 was obvious only at the delivery site and primarily within 1 d after labelling. An observed increase in the abundance of mycorrhizal fungi in the lime treatment was a possible cause for this faster carbon throughput. The potential key role of mycorrhizas in the soil carbon cycle is discussed. The importance of a better understanding of soil processes, especially biological ones, in relation to the global carbon cycle and environmental change is highlighted.