Assessent of pools and turnover of soil organic carbon

We are interested in two levels of SOC dynamics: decadal turnover rates and year-to-year variation of C-input and SOC turnover.

Decadal turnover rates

At plot initiation we took bulk soil samples in 1997 for analyses of total and 14C isotopes of SOC in each plot and in soil shafts in a subset of the plots. Undisturbed samples for bulk densities were collected to make calculations of soil carbon on a volume basis. We use the degree to which 14C from thermonuclear weapon testing in the early 1960s has infiltrated SOC, to assess the amount of organic matter turning over on decadal and shorter timescales (as compared to millennial and longer timescales). SOC 14C content is a more sensitive indicator of carbon dynamics than C inventory measurements (Trumbore et al., 1995).

Season and Interrannual variation in carbon fluxes

To assess rates of soil carbon losses via respiration, we measure soil respiration using static chambers at 6 of the study plots bimonthly, 2 of each soil type. We sample CO2 with depth in the soil shafts bimonthly using gas chromotograph to evaluate CO2 storage in the soil and partitioning of soil CO2 production with depth.