Department of Soil Ecology, University of Bayreuth, 95440 Bayreuth, Germany.
Ecol Appl. 2011 Mar;21(2):391-401. doi: 10.1890/09-1251.1.
We simulated the effect of prolonged dry summer periods by lowering the water table on three manipulation plots (D(1-3)) in a minerotrophic fen in southeastern Germany in three years (2006-2008). The water table at this site was lowered by drainage and by excluding precipitation; three nonmanipulated control plots (C(1-3)) served as a reference. We found no significant differences in soil respiration (R(Soil)), gross primary production (GPP), or aboveground respiration (R(AG)) between the C(1-3) and D(1-3) plots in any of the measurement years. The 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 (C(1-3)) 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 R(Soil) 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 R(Soil) irrespective of treatment. The results showed a significant correlation between R(Soil) and water table, but with R(Soil) decreasing at lower water tables rather than increasing. We thus conclude that decomposition in the litter layer is not limited by waterlogging 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).
我们通过在德国东南部的一个矿质沼泽中在三年（2006-2008 年）的三个处理地块（D（1-3））中降低地下水位来模拟长期干旱夏季的影响。该地点的地下水位通过排水和排除降水而降低；三个未受干扰的对照地块（C（1-3））作为参考。在任何测量年份中，我们都没有发现 C（1-3）和 D（1-3）地块之间的土壤呼吸（R（Soil））、总初级生产力（GPP）或地上呼吸（R（AG））有显着差异。对照地块的地下水位自然较低，2006-2008 年期间地下水位中位数为地表以下 8 厘米，夏季呼吸活动最高时甚至更低，地表以下中位数值（C（1-3））为 11 至 19 厘米。如果假设最上层 10 厘米的氧气供应不受地下水位位置的限制，那么人为降低地下水位很可能仅在更深的泥炭层中增加氧气供应，我们预计 R（Soil）会受到较差的基质质量而不是缺氧的限制。这可以解释缺乏操纵效果的原因。在第二种方法中，我们估计了地下水位对 R（Soil）的影响，而与处理无关。结果表明，R（Soil）与地下水位之间存在显着相关性，但随着地下水位的降低，R（Soil）而不是增加而降低。因此，我们得出结论，夏季的涝渍不会限制凋落物层的分解，而由于基质质量差，深层泥炭层没有显著的分解潜力。因此，我们预计由于干旱夏季的频率增加，该地点不会增加 C 损失。地上植被的同化和呼吸不受 10 至> 60 厘米深度之间地下水位波动的影响，表明无论是缺氧（高地下水位）还是干旱（低地下水位）都没有造成压力。
