Response of dissolved organic matter in the forest floor to long-term manipulation of litter and throughfall inputs
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Dissolved organic matter (DOM) contributes to organic carbon either stored in mineral soil horizons or exported to the hydrosphere. However, the main controls of DOM dynamics are still under debate. We studied fresh leaf litter and more decomposed organic material as the main sources of DOM exported from the forest floor of a mixed beech/oak forest in Germany. In the field we doubled and excluded aboveground litter input and doubled the input of throughfall. From 1999 to 2005 we measured concentrations and fluxes of dissolved organic C and N (DOC, DON) beneath the Oi and Oe/Oa horizon. DOM composition was traced by UV and fluorescence spectroscopy. In selected DOM samples we analyzed the concentrations of phenols, pentoses and hexoses, and lignin-derived phenols by CuO oxidation. DOC and DON concentrations and fluxes almost doubled instantaneously in both horizons of the forest floor by doubling the litter input and DOC concentrations averaged 82 mg C l−1 in the Oe/Oa horizon. Properties of DOM did not suggest a change of the main DOM source towards fresh litter. In turn, increasing ratios of hexoses to pentoses and a larger content of lignin-derived phenols in the Oe/Oa horizon of the Double litter plots in comparison to the Control plots indicated a priming effect: Addition of fresh litter stimulated microbial activity resulting in increased microbial production of DOM from organic material already stored in Oe/Oa horizons. Exclusion of litter input resulted in an immediate decrease in DOC concentrations and fluxes in the thin Oi horizon. In the Oe/Oa horizon DOC concentrations started to decline in the third year and were significantly smaller than those in the Control after 5 years. Properties of DOM indicated an increased proportion of microbially and throughfall derived compounds after exclusion of litter inputs. Dissolved organic N did not decrease upon litter exclusion. We assume a microbial transformation of mineral N from throughfall and N mineralization to DON. Increased amounts of throughfall resulted in almost equivalently increased DOC fluxes in the Oe/Oa horizon. However, long-term additional throughfall inputs resulted in significantly declining DOC concentrations over time. We conclude that DOM leaving the forest floor derives mainly from decomposed organic material stored in Oe/Oa horizons. Leaching of organic matter from fresh litter is of less importance. Observed effects of litter manipulations strongly depend on time and the stocks of organic matter in forest floor horizons. Long-term experiments are particularly necessary in soils/horizons with large stocks of organic matter and in studies focusing on effects of declined substrate availability. The expected increased primary production upon climate change with subsequently enhanced litter input may result in an increased production of DOM from organic soil horizons.
KeywordsDissolved organic matter Field experiment Forest soil Hexoses Lignin Litter Pentoses Phenols
We would like to thank Uwe Hell for help in the field and J.-H. Park for his work in the first 2 years of the experiment. Many colleagues and students of our department helped in sample preparation and analysis. We thank the members of the Central Analytical Department of BayCEER for support and Gunnar Lischeid for providing throughfall data. Egbert Matzner, Ludwig Haumaier, Klaus Kaiser, Thorsten Scheel, Thimo Klotzbücher, Susan Crow and Bruce Caldwell gave us valuable comments to an earlier version of this manuscript. We gratefully acknowledge the financial support by the German Ministry of Education and Research (BMBF) under grant No PT BEO 51-0339476.
- Chantigny MH, Angers DA, Kaiser K, Kalbitz K (2007) Extraction and characterization of dissolved organic matter. In: Carter MR, Gregorich EG (eds) Soil sampling and methods of analysis, chap 48. CRC Press, pp 617–635Google Scholar
- Gerstberger P, Foken T, Kalbitz K (2004) The Lehstenbach and Steinkreuz catchments in NE Bavaria, Germany. In: Matzner E (ed) Biogeochemistry of forested catchments in a changing environment: a German case study. Ecol Stud, vol 172. Springer Verlag, Berlin Heidelberg, pp 15–44Google Scholar
- Haider KM, Guggenberger G (2005) Organic matter. Genesis and formation. In: Hillel D (ed) Encyclopedia of soils in the environment, vol 3. Elsevier, pp 93–101Google Scholar
- Huang WZ, Schoenau JJ (1996) Distribution of water-soluble organic carbon in an aspen forest soil. Can J For Res 26:1266–1272Google Scholar
- Huang JH, Kalbitz K, Matzner E (2008) Mobility of trimethyllead and total lead in the forest floor. Soil Sci Soc Am J (in press)Google Scholar
- Mejbaum W (1939) Über die Bestimmung kleiner Pentosemengen, insbesondere in Derivaten der Adenylsäure. Z Physiol Chemie 258:117–120Google Scholar
- Scheel T, Dörfler C, Kalbitz K (2007) Precipitation of dissolved organic matter by Al stabilizes carbon in acidic forest soils. Soil Sci Soc Am J 71:64–74Google Scholar
- Tipping E, Woof C, Rigg E, Harrison AF, Ineson P, Taylor K, Benham D, Poskitt J, Rowland AP, Bol R, Harkness DD (1999) Climatic influences on the leaching of dissolved organic matter from upland UK moorland soils, investigated by a field manipulation experiment. Environ Int 25:83–95CrossRefGoogle Scholar
- WRB (2006) World reference base for soil resources 2006. World Soil Resources Reports 103, FAO, RomeGoogle Scholar