Moist substrate was packed into PVC growth columns (5.6 cm diameter and 50 cm height) to a bulk density of 1.25Mgm−3;
after planting, it was covered with a 1 cm isolation layer of Perlit (PePe® Pflanzen Perlit, Otto Hauenstein SamenAG, Rafz-
Biberist-Landquart-Orbe, Switzerland)