Quantification and process analysis of biogenic trace gas fluxes
Final Report Abstract
Our findings on freezing/thawing effects in the spruce forest soil did not support the hypothesis of additional C losses after freeze/thaw cycles. In fact, we observed lower soil CO2 emission rates mostly in the year following the frost event as compared to the unfrozen control. The reduced CO2 emission was mostly related to a considerable reduction of heterotrophic respiration. With regard to N the picture is different. Frost induced increased emissions of N2O. The N2O originates not from easily decomposable organic matter in the organic layer as repeatedly postulated in the literature, but from the subsoil. The frozen soil obviously serves no longer as a microbial sink for N2O on its diffusive way to the soil surface. Our field and laboratory experiments indicate that drying/rewetting events and irrigation in a spruce forest soil considerably affect biogenic trace gas production/consumption processes and cumulative trace gas fluxes on an annual scale. The response to drying/rewetting is specific for each of the investigated trace gases. CO2: Drought significantly reduces soil respiration. Heterotrophic respiration is more affected by drought than rhizosphere respiration. The drought effect on soil CO2 emission continues for months after rewetting probably due to continued hydrophobicity of soil organic matter. Thus, drought events become clearly visible in the annual balance of soil respiration. In contrast, continuous wetting of the soil by irrigation increases CO2 emissions. The accumulated or non-mineralized organic substrates during drought periods lead not to additional CO2 effluxes in the following year. N2O: Drought reduces N2O emissions or even turns a spruce forest soil to a transient N2O sink due to reduced N2O production but continued N2O consumption by microbial denitrification. The gross rate of N2O consumption during drought periods is possibly of large importance for the greenhouse gas budget of forests. NO: NO emissions from the spruce forest soil exceed N2O emissions by one order of magnitude. NO emissions reach a maximum at intermediate soil moisture conditions of about 33 % water-filled pore space. CH4: The spruce forest soil serves as a sink for CH4 due to microbial CH 4 oxidation. The sink function increases under drought conditions. Biogenic trace gas production/consumption processes and cumulative fluxes in the soil of a minerotrophic fen respond essentially different to drying/rewetting and flooding events. CO2 emission from soil respiration in the fen was neither affected by water table lowering nor by rewetting events. However, flooding reduced CO2 emissions considerably, indicating that soil respiration in the top peat layer is very sensitive to the O2 supply. Peat decomposition and root respiration respond similarly to flooding. N2O emissions from the fen increase after moderate lowering of the water table, while severe water table lowering and flooding decrease N2O emissions. N2O emissions in the fen are the result of simultaneous microbial N2O production and consumption in the soil profile. NO emissions from the fen are by one order of magnitude lower than in the forest and mostly driven by temperature. The fen soil is a source for CH4. Lowering of the water table reduces CH4 emission while flooding over two years increases CH 4 emissions.
Publications
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(2008) Fluxes of climate-relevant trace gases between a Norway spruce forest soil and atmosphere during freezing/thawing cycles in mesocosms. Journal of Plant Nutrition and Soil Science 171: 729-739
Goldberg S., J. Muhr, W. Borken, and G. Gebauer
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(2008) N2O concentration and isotope signature along profiles provide deeper insight into the fate of N2O in soils, Isotopes Environm. Health Studies 44: 377-391
Goldberg S., K.H. Knorr and G. Gebauer
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2008. Repeated drying/rewetting cycles and their effects on the emission of CO2, N2O, NOx and CH4 in a forest soil. Journal of Plant Nutrition and Soil Science 171: 719-759
Muhr J., S. Goldberg, W. Borken. and G. Gebauer
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(2009) Delayed recovery of soil respiration after wetting of dry soil further reduces C losses from a Norway spruce forest soil. Journal of Geophysical Research-Biogeoscience 114: G04023
Muhr J. and W. Borken
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(2009) Drought turns a Central European Norway spruce forest soil from an N2O source to a transient N2 O sink. Global Change Biology 15: 850–860
Goldberg S.D. and G. Gebauer
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(2009) Effects of soil frost on soil respiration and its radiocarbon signature in a Norway spruce forest soil. Global Change Biology 15: 782-793
Muhr J., W. Borken and E. Matzner
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(2009) N2O and NO fluxes between a Norway spruce forest soil and atmosphere as affected by prolonged summer drought. Soil Biology & Biochemistry 41: 1986-1995
Goldberg S.D. and G. Gebauer
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(2009) Reappraisal of drying and wetting effects on C and N mineralisation and fluxes in soils. Global Change Biology 15: 808-824
Borken W. and E. Matzner
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(2009) Responses of CO2 exchange and primary production of the ecosystem components to environmental changes in a mountain peatland. Ecosystems 12, 590-603
Otieno D.O., M. Wartinger, A. Nishiwaki, M.Z. Hussain, J. Muhr, W. Borken and G. Lischeid
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(2010) Drying/rewetting events reduce C and N losses from a Norway spruce forest floor. Soil Biology & Biochemistry 42: 1303-1312
Muhr J., J. Franke and W. Borken
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(2010) Impact of altering the water table height of an acidic fen on N2O and NO fluxes and soil concentrations, Global Change Biology 16: 220-233
Goldberg S. K.H. Knorr, C. Blodau, G. Lischeid and G. Gebauer
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(2010) N2O emission in a Norway spruce forest due to soil frost – Concentration and isotope profiles shed a new light on an old story. Biogeochemistry 97: 21- 30
Goldberg S.D., W. Borken and G. Gebauer
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(2011) Manipulative lowering of the water table during summer does not affect CO2 emissions and uptake in a minerotrophic fen in South-eastern Germany. Ecological Applications 21: 391-401
Muhr J., J. Höhle, D.O. Otieno and W. Borken
