Response of N turnover, DOC production and soil solution fluxes
Final Report Abstract
The findings from the laboratory and field experiments concerning the spruce forest did generally not confirm the hypotheses of the first and second period of this project. In contrast, freezing/thawing or drying/wetting had either no or even opposite effects on the turnover and fluxes of C and N on an annual scale. Frequently, in the literature reported flushes of C and N compounds following thawing of frozen soils or wetting of dried soils were not found, indicating that the microbial organisms of the spruce forest soil are well adapted to these stress periods. We must, however, restrict these findings to the forest floor and the top ~10-15 cm of the mineral soil as the treatments in the field had no or little effect on the mineral soil below this depth. The laboratory results suggest that at least a strong desiccation of the mineral soil negatively affected the nitrification rate. The discrepancy between the findings from our laboratory and field studies can be attributed to differences in water fluxes (in particular relevant for DOC fluxes), in the intensity of drying or freezing. Still unclear is why gross N turnover responded stronger to similar soil desiccation under laboratory than under field conditions. We speculated that the heterogeneity of gross N turnover rates in the field overshadowed the desiccations effects. Nevertheless, our results indicate that net N turnover and N fluxes in soil solution are barely affected by extended drought periods compared to C mineralization. Annual leaching rates of inorganic N were not different between the throughfall exclusion and control plots on annual scale. Consequently, enhanced N net mineralization and nitrification rates in autumn and winter compensate reduced rates during the drought period. C mineralization was strongly reduced during the drought treatments and for up to 2-3 months thereafter as hydrophobicity and preferential flow caused a slow recovery of soil moisture in the forest floor. In summary, the forest floor and its physiochemical properties have a dominating effect on the response of matter turnover and fluxes of spruce forests owing to extreme meteorological events. The response of the fen to water table drawdown and flooding must be viewed with regards to the disturbances by drainage and peat degradation. Water table manipulations controlled the O2 supply and thus redox-sensitive concentrations of SO4^2- and Fe^n+ whereas the responsible mechanism beyond the control of DOC concentration is not clarified. It seems that changes in the ion and DOC concentration in the peat below ~10 cm depth have little influence on the export of solutes as but there are hints that the export of solutes is mainly restricted to surface runoff. Concentrations of NH4^+ and NO3^- were small despite relatively great gross N mineralization rates under flooded conditions. Flooding increased gross N mineralization, indicating that the N turnover is largely decoupled of the C turnover. Overall, water table drawdown and flooding considerably altered the internal turnover of ions.
Publications
- (2007) Leaching losses of inorganic N and DOC following repeated drying and wetting of a spruce forest soil. Plant and Soil 300: 21-34
Hentschel K., W. Borken and E. Matzner
- (2008) Do freeze/thaw events enhance C and N losses from boreal and temperate soils? European Journal of Soil Science 59: 274-284
Matzner E. and W. Borken
- (2008) Repeated freeze/thaw cycles change organic matter quality in a temperate forest soil. Journal of Plant Nutrition and Soil Science 171: 709-718
Schmitt A., B. Glaser, W Borken and E. Matzner
- (2008) Repeated frost/thaw events and their effects on leaching losses of nitrogen and dissolved organic matter in a forest soil. Journal of Plant Nutrition and Soil Science 171: 699-706
Hentschel K., W. Borken and E. Matzner
- (2009) Effects of soil frost on nitrogen net mineralization, soil solution chemistry and seepage losses in a temperate forest soil. Global Change Biology 15: 825-836
Hentschel K., W. Borken, T. Zuber, C. Bogner, B. Huwe and E. Matzner
- (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
- (2009) Stock, turnover and accumulation of organic matter in bulk and density fractions of a Podzol soil. European Journal of Soil Science 60: 567-577
Schulze K., W. Borken, J. Muhr and E. Matzner
- (2010) Organic matter quality or a forest soil subjected to repeated drying and different rewetting intensities. European Journal of Soil Science 61: 243-254
Schmitt A., Glaser B., Borken W. and E. Matzner
- (2011) Dynamics of dissolved organic 14C signature in throughfall and soil solution of a Norway spruce forest. Biogeochemistry
Schulze K., W. Borken and E. Matzner
(See online at https://dx.doi.org/10.1007/s10533-010-9526-2) - (2011) Effects of decreasing water potential on gross ammonification and nitrification in an acid coniferous forest soil. Soil Biology Biochemistry 43: 333- 338
Chen Y.T., W. Borken, C.F. Stange and E. Matzner
- (2011) Organic matter dynamics in a temperate forest following enhanced drying. Soil Biology and Biochemistry 43: 478-489
Schmitt A., and B. Glaser
- Organic matter dynamics in a temperate forest as influenced by soil frost. Journal of Plant Nutrition and Soil Science
Schmitt A., and B. Glaser
(See online at https://doi.org/10.1002/jpln.201100009)
