Fluxes of climate-relevant trace gases between a Norway spruce forest soil and atmosphere during repeated freeze-thaw cycles in mesocosms

• Published in: Journal of plant nutrition and soil science 2008-10, Vol.171 (5), p.729-739
• Main Authors: Goldberg, Stefanie D, Muhr, Jan, Borken, Werner, Gebauer, Gerhard
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; CO2 / N2O; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; soil frost; Soil science; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; thawing
• ISSN: 1436-8730; 1522-2624
• DOI: 10.1002/jpln.200700317

For this century, an increasing frequency of extreme meteorological boundary conditions is expected, presumably resulting in a changing frequency of freezing and thawing of soils in higher-elevation areas. Our current knowledge about the effects of these events on trace-gas emissions from soils is scarce. In this study, the effects of freeze-thaw events on the fluxes of the trace gases CO₂, N₂O, and NO between soil and atmosphere were investigated in a laboratory experiment. Undisturbed soil columns were collected from a mature Norway spruce forest in the "Fichtelgebirge", SE Germany. The influence of freezing temperatures (-3°C, -8°C, -13°C) on gas fluxes was studied during the thawing periods (+5°C) in three freeze-thaw cycles (FTCs) and compared to unfrozen controls (+5°C).Two different types of soil columns were examined in parallel--one consisting of O layer only (O columns) and one composed of O layer and mineral soil horizons (O+M columns)--to quantify the contribution of the organic layer and the top mineral soil to the production or consumption of these trace gases.During the thawing period, we observed increasing emissions of CO₂, N₂O, and NO from the spruce forest soil, but the cumulative emissions of these gases did mostly not exceed the level of the controls. The results show that the O layers were mainly involved in the gas production. Severe soil frost increased CO₂ fluxes during soil thawing, whereas repetition of the freeze-thaw events decreased CO₂ fluxes from the thawing soil. Fluxes of N₂O and NO were neither influenced by freezing temperature nor by freeze-thaw repetition.Stable-isotope analysis indicated that denitrification was mostly responsible for the N₂O production in the FTC columns. Furthermore, isotope data demonstrated a consumption of N₂O through microbial denitrification to N₂. It was further shown, that production of N₂O also occurred in the mineral horizons. The NO emissions were mainly driven by increasing soil temperature during thawing. In this freeze-thaw experiment up to 20 times higher NO than N₂O fluxes were recorded. Our results suggest that topsoil thawing has little potential to increase the emissions of CO₂, N₂O, and NO in spruce forest soils.