Ligninabbau als Steuergröße der C-Mineralisierung und Produktion gelöster organischer Substanz in Humusauflagen
Zusammenfassung der Projektergebnisse
Lignin is a major component of plant litter. Biodegradation of lignin is thought to be a main control of overall plant litter decomposition in forest floor horizons. Traditionally, in studies on litter decomposition `lignin` was analysed as acid unhydrolyzable residue (AUR; e.g. Klason lignin, van Soest method). We incubated leave and needle litter of 5 species (ash, beech, maple, pine, spruce) for 27 months in litterbags at a spruce site in Germany. We could show on these samples that recent, molecular analytical approaches to study lignin degradation (CuO method, 13C-TMAH thermochemolysis) reveal a different picture on the fate of lignin in plant litter than AUR analysis. In particular, the long assumed selective preservation of lignin during the first months of litter decomposition, based on AUR analysis, was not supported by results from the CuO and 13C-TMAH methods. Subsequently, litter residues of different decomposition degree derived from the litterbag experiment (i.e., field exposure for 0, 3, 12 and 27 months before laboratory incubation) were incubated for 2 years in the laboratory at constant water content (60% of maximum water holding capacity) and temperature (20 °C). Lignin degradation was followed using the CuO method and related to concentrations of dissolved organic C (DOC) in water extracts and CO2 evolution. Strong lignin degradation occurred during the first 200 incubation days, as revealed by decreasing yields of lignin-derived phenols. Thereafter lignin degradation levelled off. This pattern was similar for fresh and decomposed litter, and contrasts the common view of limited lignin degradation in fresh litter. Dissolved organic carbon and CO2 also peaked in the first period of the incubation but were not interrelated. In the later phase of incubation, CO2 production was positively correlated with DOC amounts, suggesting that bioavailable, soluble compounds became a limiting factor for CO2 production. Lignin degradation occurred only when CO2 production was high, and not limited by bioavailable carbon. Thus carbon availability was the most important control on lignin degradation. Our results challenge the traditional view regarding the fate and role of lignin during litter decomposition. Lignin degradation is controlled by the availability of easily decomposable carbon sources. Consequently, it occurs particularly in the initial phase of litter decomposition and is hampered at later stages if easily decomposable resources decline. We furthermore studied the effect of manipulated litter input on lignin degradation in forest floors of different temperate forests. At a beech/oak site in Germany (Steinkreuz), litter addition led to enhanced DOM production in Oa horizons and the DOM was enriched in lignin phenols, suggesting that enhanced litter input triggered lignin degradation in the lower part of the forest floor. Also at a spruce site in Germany, enhanced litter input changed decomposition processes as indicated by altered DOM production and shifts in DOM properties in the forest floor profile. Overall our data imply that stocks of organic matter in forest floors of temperate forests will not change according to the changes in litter input. These findings are critical for the evaluation of climate change effects on the C balance of temperate forests because it can be expected that plant litter inputs will generally increase in temperate regions due to a positive response of plant productivity to increasing atmospheric CO2 levels and temperatures.
Projektbezogene Publikationen (Auswahl)
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A study of lignin degradation in leaf and needle litter using 13C-labelled tetramethylammonium hydroxide (TMAH) ther-mochemolysis: Comparison with CuO oxidation and van Soest methods. Organic Geochemistry, 42, 1271-1278
Klotzbücher, T.; Filley, TR; Kaiser, K; Kalbitz, K.
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Effects of throughfall and litterfall manipulation on concentrations of methylmercury and mercury in forest floor percolates. J. Plant Nutr. Soil Sci. 170, 373-377 (2007)
Hojdová, M., Huang, J.-H., Kalbitz, K. Matzner, E.
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Response of dissolved organic matter in the forest floor to long-term manipulation of litter and throughfall inputs. Biogeochemisty, 86, 301-318 (2007)
Kalbitz, K.; Meyer, A.; Yang, R.; Gerstberger, P.
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Mobility of trimethyllead and total lead in the forest floor. Soil Sci. Soc. Am. J. 72, 978-984 (2008)
Huang, J. H., Kalbitz, K. Matzner, E.
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Comparability of commonly used methods to study lignin degradation in decomposing foliar litter. Geochim Cosmochim. Acta 74, A524 (2010)
Klotzbücher, T., Kaiser, K. Filley, T. R., Kalbitz K.
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A new conceptual model for the fate of lignin in decomposing plant litter. Ecology, 92, 1052-1062 (2011)
Klotzbücher, T; Kaiser, K; Guggenberger, G; Gatzek, C; Kalbitz, K
