Root-growth Inhibition Effects of Holorganic Moder Humus Layer Under Spruce (picea-abies Karst) and Beech (fagus-sylvatica L) .1. Field Observations and Growth Chamber Experiments

Field observations demonstrated inhibition of root growth by moder humus material of the Of2 and Oh-layers under beech and spruce. Growth chamber experiments with spruce seedlings showed that root growth on a natural Of2-substrate is ten times lower than on resin-quartz mixtures. Added phenolic acid (protocatechic a.) inhibited root growth only in sterilized substrate. Leachates of Of2-material inhibited root growth in a mineral substrate devoid of absorption complex (pure quartz sand), but not in a resin-quartz mixture. It is concluded that inhibiting substances are probably ionized molecules that can withstand biodegradation.