Soil Biology and Biochemistry, Feb, 2013, Vol.57, p.1(13)
To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.soilbio.2012.06.018 Byline: Alexander Dumig (a), Cornelia Rumpel (b), Marie-France Dignac (b), Ingrid Kogel-Knabner (a)(c) Abstract: .sup.13C contents of organic matter are changing during decomposition of plant material and stabilization as soil organic carbon (SOC). In this context, several studies showed.sup.13C enrichment in soil as compared to vegetation for C.sub.3 forests, whereas depletion of.sup.13C was frequently reported for C.sub.4 grassland soil as compared to C.sub.4 vegetation. These changes were often attributed to selective preservation and/or stabilization of specific organic compounds. This study investigates if changes in the chemical composition of OC and specifically lignin may explain the observed shifts in [delta].sup.13C values from plant material to SOC. We analyzed aboveground biomass, roots and heavy organo-mineral fractions from topsoils in both, long-term stable C.sub.4 grasslands and C.sub.3 Araucaria forest situated nearby in the southern Brazilian highlands on soils with andic properties. The stable carbon isotope (.sup.12C/.sup.13C) composition was analyzed for total organic carbon (OC.sub.tot) and lignin-derived phenols. The bulk chemical composition of OC was assessed by solid-state.sup.13C NMR spectroscopy while neutral sugar monomers were determined after acid hydrolysis. The shifts of the.sup.13C/.sup.12C isotope signature during decomposition and stabilization (plant tissues versus soil heavy fractions) showed similar trends for VSC phenols and OC.sub.tot (.sup.13C depletion in C.sub.4 grassland soil and.sup.13C enrichment in C.sub.3 forest soil compared to the corresponding vegetation). In this regard, the isotopic difference between roots and aboveground biomass was not relevant, but may become more important at greater soil depths..sup.13C depletion of VSC lignins relative to OC.sub.tot was higher in C.sub.3-biomass and C.sub.3-derived SOC compared to the C.sub.4 counterparts. As lignin contents of heavy fractions were low, in particular for those with C.sub.4 isotopic signature, the influence of lignin on OC.sub.tot [delta].sup.13C values in grassland topsoils is presumably low. Rather, the presence of charred grass residues and the accumulation of alkyl C in heavy fractions as revealed by.sup.13C NMR spectroscopy contribute to decreasing [delta].sup.13C values from grass biomass to C.sub.4-derived heavy fractions. In forest topsoils, the accumulation of.sup.13C depleted VSC lignin residues in heavy fractions counteracts the prevailing.sup.13C enrichment of OC.sub.tot from plant biomass to heavy fractions. Nonetheless, non-lignin compounds with relatively high.sup.13C contents like microbial-derived OC have a stronger influence on [delta].sup.13C values of OC.sub.tot in forest soils than lignins or aliphatic biopolymers. The mineral-associated SOC is in a late phase of decomposition with large contributions of microbial-derived carbohydrates, but distinct structural and isotopical alterations of lignin between C.sub.4- and C.sub.3-derived heavy fractions. This may indicate different processes and/or extent of lignin (and SOM) biodegradation between C.sub.4 grassland and C.sub.3 forest resulting from other kind of decomposer communities in association with distinct types and amounts of plant input as source of SOM and thus, carbon source for microbial transformation. Our results indicate that the importance of lignin for [delta].sup.13C values of OC.sub.tot was overestimated in previous studies, at least in subtropical C.sub.4 grassland and C.sub.3 forest topsoils. Author Affiliation: (a) Lehrstuhl fur Bodenkunde, Department fur Okologie und Okosystemmanagement, Wissenschaftszentrum Weihenstephan fur Ernahrung, Landnutzung und Umwelt, Technische Universitat Munchen, D-85350 Freising-Weihenstephan, Germany (b) CNRS-INRA, Laboratoire de Biogeochimie et Ecologie des Milieux Continentaux (UMR 7618, UPMC-CNRS-UPEC-ENS-INRA-AgroParisTech), Centre INRA - Batiment EGER de Versailles-Grignon, F-78850 Thiverval-Grignon, France (c) Institute for Advanced Study, Technische Universitat Munchen, Lichtenbergstrasse 2a, D-85748 Garching, Germany Article History: Received 5 April 2012; Revised 26 June 2012; Accepted 29 June 2012
Biodegradation -- Analysis ; Lignin -- Analysis ; Grasslands -- Analysis ; Biopolymers -- Analysis ; Marine Safety -- Analysis ; Forest Soils -- Analysis ; Nuclear Magnetic Resonance Spectroscopy -- Analysis ; Alkyl Groups -- Analysis ; Hydrolysis -- Analysis ; Soil Carbon -- Analysis
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