Experimental set-up.

40 intact vertical soil cores were collected in 4 drained fens using sharpened PVC tubes (45 x 12.5 cm), and were then placed in individual containers filled with stagnant de-oxygenized artificial groundwater. Tubes were perforated at the bottom to allow water inflow. Rhizons were placed at 5, 15 and 25 cm below the soil surface, and connected to vacuum-syringes. Half of the cores were rewetted to peat surface level, while the other half was kept moderately drained (water level 27 cm below peat surface level).