Uni-Bayreuth grafik-uni-bayreuth


Glaser, B*; Schmitt, A; Goldberg, S; Muhr, J; Hentschel, K; Bogner, C; Zuber, T; Gaul, D; Borken, W; Gebauer, G; Huwe, B; Hertel, D; Leuschner, C; Matzner, E: Soil processes in a Norway spruce forest as affected by freezing and thawing
Vortrag, International Symposium Soil processes under extreme meteorological conditions, Bayreuth: 25.02.2007 - 28.02.2007

The frequency of extreme climatic events such as intensive freezing without snow cover or frequent thawing periods during winter may increase in the near future. Here we investigated the effect of soil frost on C and N dynamics of a Haplic Podsol under a spruce forest (Picea abies) in the Fichtelgebirge, Germany. At the field site, a maximum frost intensity of -5°C, ﷓3°C and about 0 °C was induced at 5, 15, and 25 cm soil depth, respectively, by removing the snow cover during a three months period between January and March 2006 while the controls never were below 0 °C. Additionally, undisturbed soil columns (15 cm and 30 cm depths) from this forest were subjected to different frost intensities of -3, -8, -13°C and +5°C in the control in three freeze/thaw cycles. Subsequently, all columns were thawed at +5°C and irrigated with 80 mm water at 4 mm per day, corresponding to an average rainfall of the investigation area. Under field conditions, freezing induced a significant reduction in CO2 emission of 182 g m-2 a-1 from soil continuing also after the experiment, while a 20-fold increase in N2O emission (0.1 vs. 2 mmol m-2 h-1) was observed, being mainly due to denitrification as revealed by compound-specific δ15N and δ18O analyses. This was corroborated by higher NO3- concentrations in the soil solution while freezing had no effect on concentrations of dissolved organic carbon (DOC) and NH4+. Also, intensive freezing did not influence total organic carbon (TOC) content in soil as revealed by freezing / thawing cycles of different frost intensities on undisturbed soil columns under controlled conditions in the laboratory. However, the distribution and release of stable (VSC lignin) and labile (plant- and microbially derived sugars, microbial biomass and composition) SOM pools significantly changed upon freezing and thawing. The soluble export of lignin into DOM significantly increased with increasing freezing intensity. As no changes of the acid to aldehyde ratio of lignin moieties could be observed, the increased solubilization was certainly due to manipulation (abiotic effect) indicating a destabilization of a relatively stable SOM pool upon increase of frost intensity. Additionally, freezing induced a 30% increase of root necromass compared to the control sites probably also contributing to an increase of soluble lignin. However, root decomposition was similar to as in non-frozen control sites.

Letzte Änderung 19.03.2007