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Faculty for Biology, Chemistry and Earth Sciences

Department Soil Ecology - Prof. Dr. Eva Lehndorff

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Muhr, J; Höhle, J; Otieno, DO; Borken, W: 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 (2011), doi:10.1890/09-1251.1
We simulated the effect of prolonged dry summer periods by lowering the water table on three manipulation plots (D1-3) in a minerotrophic fen in South-eastern Germany in three subsequent years (2006 2008). The water table at this site was lowered by drainage and by excluding precipitation; three nonmanipulated control plots (C1-3) served as a reference. We found no significant differences in soil respiration (RSoil), gross primary production (GPP) and aboveground respiration (RAG) between the C1-3 and D1-3 plots in any of the measurement years. Water table on the control plots was naturally low, with a median water table (2006 2008) of 8 cm below the surface, and even lower during summer when respiratory activity was highest, with median values (C1 3) between 11 and 19 cm below the surface. If it is assumed that oxygen availability in the uppermost 10 cm was not limited by the location of the water table, manipulative lowering of the water table most likely increased oxygen availability only in deeper peat layers where we expect RSoil to be limited by poor substrate quality rather than anoxia. This could explain the lack of a manipulation effect. In a second approach, we estimated the influence of the water table on RSoil irrespective of treatment. The results showed a significant correlation between RSoil and water table, but with RSoil decreasing at lower water tables rather than increasing. We thus conclude that decomposition in the litter layer is not limited by water logging in summer and deeper peat layers bear no significant decomposition potential due to poor substrate quality. Consequently, we do not expect enhanced C losses from this site due to increasing frequency of dry summers. Assimilation and respiration of aboveground vegetation were not affected by water table fluctuations between 10 and >60 cm depth, indicating the lack of stress resulting from either anoxia (high water table) or drought (low water table). Keywords: climate change, CO2 emission, CO2 uptake, ecosystem manipulation, fen, Peat decomposition, water table lowering
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