Title: Chemical and mineral control of soil carbon turnover in abandoned tropical pastures.
Author: Marín-Spiotta, Erika; Swanston, Christopher W.; Torn, Margaret S.; Silver, Whendee L.; Burton, Sarah D.
Date: 2007
Source: Geoderma, doi:10.1016/j.geoderma.2007.10.001
Description: We investigated changes in soil carbon (C) cycling with reforestation across a long-term, replicated chronosequence of tropical secondary forests
regrowing on abandoned pastures. We applied CP MAS 13C NMR spectroscopy and radiocarbon modeling to soil density fractions from the top
10 cm to track changes in C chemistry and turnover during secondary forest establishment on former pastures. Our results showed that interaggregate,
unattached, particulate organic C (free light fraction) and particulate C located inside soil aggregates (occluded light fraction) represent
distinct soil C pools with different chemical composition and turnover rates. The signal intensity of the O-alkyl region, primarily representing
carbohydrates, decreased, and alkyl C, attributed to recalcitrant waxy compounds and microbially resynthesized lipids, increased from plant litter to
soil organic matter and with incorporation into soil aggregates. The alkyl/O-alkyl ratio, a common index of humification, was higher in the occluded
than in the free light fraction. Greater variability in the chemical makeup of the occluded light fraction suggests that it represents material in varied
stages of decomposition. Mean residence times (14C-based) of the free light fraction were significantly shorter (4±1 years) than for the heavy fraction.
We report two scenarios for the occluded light fraction, one fast-cycling in which the occluded and free light fractions have similar turnover rates, and
one slow-cycling, in which the occluded light fraction resembles the heavy fraction. Mean residence times of the occluded light fraction and heavy
fraction in active pastures and 10-year old secondary forests in the earliest stage of succession were longer than in older secondary forests and primary
forests. This is likely due to a preferential loss of physically unprotected C of more labile composition in the pastures and in the youngest successional
forests, resulting in an increase in the dominance of slow-cycling C pools. Soil carbon turnover rates of the mineral-associated C in secondary forests
recovering from abandoned pasture resembled those of primary forests in as little as 20 years of succession.
Keywords: Soil organic matter; Density fractionation; Radiocarbon; CP MAS 13C NMR spectroscopy; Reforestation; Land-use change
View and Print this Publication (423k)
Publication Notes:
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
Get the latest version of the Adobe Acrobat reader or Acrobat Reader for Windows with Search and Accessibility
Citation
Marín-Spiotta, Erika; Swanston, Christopher W.; Torn, Margaret S.; Silver, Whendee L.; Burton, Sarah D. 2007. Chemical and mineral control of soil carbon turnover in abandoned tropical pastures.. Geoderma, doi:10.1016/j.geoderma.2007.10.001.