Carbon isotopic fractionation during decomposition of plant materials of different quality

Abstract

[1] Changes in isotopic 13 C composition of solid residues and CO 2 evolved during decomposition of C 3 and C 4 plant materials were monitored over 10 months to determine carbon isotopic fractionation at successive stages of biodegradation. We selected plant materials of different chemical quality, e.g., Zea mays (leaves, stems, coarse roots, and fine roots), Lolium perenne (leaves and roots), Pinus pinaster (needles), and Cocos nucifera (coconut shell) and also characterized these by solid-state 13 C NMR. Roots were more lignified than aerial parts of the same species. Lignin was always depleted in 13 C (up to 5.2%) as compared with cellulose from the same sample. Proteins were enriched in 13 C in C 3 plants but depleted in maize. Cumulative CO 2 evolved fitted a doubleexponential model with two C pools of different lability. During early stages of decomposition, the CO 2 -C released was usually 13 C depleted as compared with the initial substrate but enriched at posterior stages. Consequently, with ongoing decomposition, the solid residue became 13 C depleted, which could only partly be explained by an accumulation of lignin-C. The extension of the initial 13 C depleted CO 2 -C phase was significantly correlated with the labile substrate C content, acid-detergent soluble fraction, and total N, pointing to a direct influence of plant quality on C isotopic dynamics during early stages of biodegradation. This isotopic fractionation can also lead to an underestimation of the contribution of plant residues to CO 2 -C when incubated in soils. We discuss possible implications of these mechanisms of 13 C fractionation in ecosystems.

Carbon isotope anomaly in the major plant C<sub>1</sub> pool and its global biogeochemical implications

“…Depletion in 13 C of lignin methoxyl groups in wood ( ∼−13‰) relative to bulk biomass was substantial although not as dramatic as that observed for lignin methoxyl groups in leaves (mean of all leaves ∼−29‰, range −20 to −38‰). These findings explains the widely reported 13 C depletion of lignin relative to other major plant components (Benner et al, 1987;Schweizer et al, 1999;Fernandez et al, 2003;Hobbie and Werner, 2004) which has previously been attributed to 13 C fractionation in aromatic amino acids involved in lignin biosynthesis. Thus assuming a methoxyl content of 15-20% a depletion of −13‰ in methoxyl carbon readily explains the observed 2-3‰ difference between δ 13 C of lignin and bulk biomass of wood.…”

“…Most CH 3 OH released from plants is derived from the ubiquitous plant component pectin by both enzymic and abiotic processes (Fall and Benson, 1996;Warneke et al, 1999;Galbally and Kirstine, 2002). Pectin which normally comprises between 7 and 35% of cell wall material in leaves is composed of galacturonic acid monomer units.…”

Evaluating carbon dynamics and microbial activity in arctic soils under warmer temperatures

“…However, recent studies indicate that significant isotopic discrimination effects exist when fungal tissues are compared with their plant substrates (Hobbie et al 1999). To date, C isotope dynamics during biological transformations of plant tissues remains mostly unexplored, and knowledge of the factors affecting the natural abundance of 13 C on soil organic matter are limited (Fernandez et al 2003).…”

Error analysis of the determination of carbon stable isotope ratios in lignin and cellulose from plant samples

“…Brendel et al (2000) applied spectroscopic methods to investigate the effectiveness of the methods used to separate lignin and cellulose, and reported that a small amount of lignin always remained in the cellulose isolates. Another potential source of error is variation of the respective abundances of cellulose and lignin, which depends mainly on the nature of the tissues (Schweizer et al, 1999;Akagi et al, 2004) and extent of decomposition (Benner et al, 1987;Schweizer et al, 1999;Akagi et al, 2004, Fernandez et al, 2003. Furthermore, varying proportions of hemi-cellulose and α-cellulose, whose isotopic signatures have not been well documented, also provides a potential source of error.…”

“…Isolation of cellulose, with subsequent δ 13 C measurement of this component, is a standard procedure for investigating the carbon isotopic composition of plants (e.g., Brendel et al, 2000;Mazany et al, 1980). Numerous published studies have reported the precision of carbon isotopic measurements of cellulose and lignin isolates from specific plant samples (Benner et al, 1987;Loader et al, 1997Loader et al, , 2003Brendel et al, 2000;Mazany et al, 1980;Hobbie and Werner, 2004;Fernandez et al, 2003;Schweizer et al, 1999;Wilson and Grinsted, 1977;Leavitt and Danzer et al, 1993). It is not surprising, however, that, to the best of our knowledge, no studies reported or estimated the accuracy of the isotopic data, because of the lack of appropriate isotopic reference materials.…”