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Isotopic ( 13 C) fractionation during plant residue decomposition and its implications for soil organic matter studies
Author(s) -
Schweizer Marina,
Fear John,
Cadisch Georg
Publication year - 1999
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/(sici)1097-0231(19990715)13:13<1284::aid-rcm578>3.0.co;2-0
Subject(s) - chemistry , fractionation , organic matter , legume , decomposition , environmental chemistry , lignin , soil organic matter , isotopic signature , isotope analysis , stable isotope ratio , botany , soil water , chromatography , environmental science , soil science , ecology , organic chemistry , physics , quantum mechanics , biology
Abstract Carbon isotopic fractionations in plant materials and those occurring during decomposition have direct implications in studies of short‐and longer‐term soil organic matter dynamics. Thus the products of decomposition, the evolved CO 2 and the newly formed soil organic matter, may vary in their 13 C signature from that of the original plant material. To evaluate the importance of such fractionation processes, the variations in 13 C signatures between and within plant parts of a tropical grass ( Brachiaria humidicola ) and tropical legume ( Desmodium ovalifolium ) were measured and the changes in 13 C content (signatures) during decomposition were monitored over a period of four months. As expected the grass materials were less depleted in 13 C (−11.4 to −11.9‰) than those of the legume (−27.3 to −25.8‰). Root materials of the legume were less (1.5‰) depleted in 13 C compared with the leaves. Plant lignin‐C was strongly depleted in 13 C compared with the bulk material by up to 2.5‰ in the legume and up to 4.7‰ in the grass. Plant materials were subsequently incubated in a sand/nutrient–solution/microbial inoculum mixture. The respiration product CO 2 was trapped in NaOH and precipitated as CaCO 3 , suitable for analysis using an automated C/N analyser coupled to an isotope ratio mass spectrometer. Significant depletion in 13 C of the evolved CO 2 was observed during the initial stages of decomposition probably as a result of microbial fractionation as it was not associated with the 13 C signatures of the measured more decomposable fractions (non‐acid detergent fibre and cellulose). While the cumulative CO 2 ‐ 13 C signatures of legume materials became slightly enriched with ongoing decomposition, the CO 2 ‐C of the grass materials remained depleted in 13 C. Associated isotopic fractionation correction factors for source identification of CO 2− C varied with time and suggested errors of 2–19% in the estimation of the plant‐derived C at 119 days of incubation in a soil of an intermediate (−20.0‰) 13 C signature. Analysis of the residual material after 119 days of incubation showed little or no change in the 13 C signature partly due to the incomplete decomposition at the time of harvesting. Copyright © 1999 John Wiley & Sons, Ltd.