Soil Carbon Inputs from a 60-year Chronosequence of Decaying Pine Roots.
Kim H. Ludovici, USDA-Forest Service, Southern Research Station, 3041 Cornwallis Road, Durham, NC 27709, Daniel D. Richter Jr., Duke Univ, Box 90328, Durham, NC 27708-0328, and Kimberly A. Magrini, National Renewable Energy Lab, 1617 Cole Blvd., Golden, CO 80401.
Samples of root biomass and co-located soil, from mature loblolly pine stands which were clear-cut from 0 to 60 years ago, were characterized with pyrolysis molecular beam mass spectrometry (py-MBMS). Determinations of constituents of soil organic matter (SOM) were made for 30 soil cores and 30 decomposing lateral roots. Mass spectra were run in triplicate and principle component analysis used to determine the correlated groups of products that track their transformation into stable constituents of SOM. The component groups of resins, cellulose, lignin and carbohydrate degradation products varied considerably within the sample set. Scores of individual mass spectrums indicate root samples are tightly grouped by chemistry, and suggest that root material from more recently harvested sites had higher loadings of lignin and carbohydrates, while roots from trees harvested 60 years ago had higher extractive and resin loadings. The overlaying spectrum explained 66% of the variance in the data set. A PLS regression model that predicts the length of time of root decomposition based on the extractives content had an r2 value of 0.90. Previous work on loblolly pine root decomposition documented a lengthy process which can be modeled with good precision as a function of ground line stump diameter and years since harvest (Ludovici et al. 2002). Results from this additional work indicate that py-MBMS can be used to differentiate carbon chemistry and to predict the length of root decomposition. The mass spectrum of a subset of co-located root and soil samples have been overlay and clearly show the similarity of the 2 samples in that soil carbon looks like the root carbon.