Lignin content and chemical characteristics in maize and wheat vary between plant organs and growth stages: consequences for assessing lignin dynamics in soil
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Assessing lignin turnover in soil on the basis of a 13C natural abundance labeling approach relies on the assumption that chemical characteristics of labeled and control plant inputs are similar and that the 13C content difference between labeled and control plant inputs is constant within the plant parts. We analyzed lignin in soils, roots, stems and leaves of wheat and maize at different stages of growth using the cupric oxide oxidation method. In both plants, lignin concentrations increased with growth, particularly during grain filling. Maize contained more cinnamyl moieties than wheat. Roots had higher lignin contents (especially cinnamyl moieties) than stems and leaves, and seemed to contribute more to the total soil lignin than the aboveground parts. The isotopic differences (∆ δ13C) of lignin phenols were not significantly different (p > 0.05) between plant organs, confirming assumptions underlying the natural abundance 13C labeling approach. Our data show that lignin content and phenol distribution can vary between plant organs and with the time of harvest. Consequently, the amount of annual lignin input may vary as a function of root amount and harvest date, and thus can affect the calculated apparent turnover times of lignin in natural abundance 13C labeling experiments.
KeywordsSoil lignin turnover C3-C4 natural abundance labeling Plant composition Roots
The Swiss National Science Foundation funded this study. The authors thank Johanna Sirch and Rudolf Obermeier (Höhere Landbauschule Rotthalmünster) for the plant and soil sampling, Michael Hilf (University of Zurich) for the technical assistance and Wolfgang Armbruster (University of Hohenheim) for the 13C isotope analysis. The authors thank also the anonymous reviewers for their helpful comments. This project was funded by the Swiss National Foundation for Science.
The study was jointly conceived by A. Heim and M. Schmidt. Samuel Abiven carried out the analysis for the plant samples and A. Heim for the soil samples. S. Abiven and A. Heim analyzed the results and S. Abiven prepared the manuscript. All authors discussed the results and commented the manuscript.
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