Soil carbon content and character in an old-growth forest in northwestern Pennsylvania: a case study introducing pyrolysis molecular beam mass spectrometry (py-MBMS).

This study was conducted to: (1) test the utility of a new and rapid analytical method, pyrolysis molecular beam mass spectrometry (py-MBMS), for the measurement and characterization of carbon in forest soils, and (2) examine the effects of natural disturbance on soil carbon dynamics. An additional objective was to test the ability of py-MBMS to distinguish recent from more stable humic substances, and to relate this information to the ecology and history of the sites. To test the utility of the py-MBMS technique, we investigated soil carbon stocks in a chronosequence of stands arising from natural disturbance in the Tionesta Scenic and Research Natural Areas. Soil carbon increased with increasing time since disturbance; although the exact shape of the carbon accumulation curve is not known, it appears that the rate of carbon accretion is initially rapid and then levels off, with a possible maximum of 86 metric tons/ha to a depth of 30 cm. This study also demonstrates that py-MBMS is a valid method for characterizing soil carbon and can be used with little sample preparation. In addition, multivariate analysis of the mass spectra from Tionesta soils can distinguish both sites and depths on the basis of their pyrolysis products; both long-lived and short-lived carbon forms were identified.