Allelochemicals in the Soil beneath Quercus mongolica Fisch var, grosseserrata

The phenomenon that wild grasses did not grow beneath the tree of Quercus mongolica Fisch var. grosseserrata Rehd. Wils. while they grew vigorously beneath other species of trees around Q. mongolica was observed in many places in the Hokkaido district. The allelochemicals in the soil beneath Q. mongolica were studied. This soil inhibited the growth of lettuce (Lactuca scariola L. var. sativa Bisch), green amaranth (Amaranthus viridis L.), wheat (Triticum aestivum cv. Normn No. 59) and timothy (Phleum pratense L.) by 50-90% in a 30 day soil culture test in phytotron. Of four fractions of extracts, the ethyl acetate fraction of the phenolic extracts from the soil beneath Q. mongolica showed the highest inhibition on seed germination and growth of etiolated seedling of the four species. Nine allelochemicals, 3,4-dihydroxybenzoic, p-hydroxybenzoic, 3,4,5-trimethoxybenzoic, 3,4-dimethoxybenzoic, vanillic, pcoumaric, ferulic acids, p-hydroxybenzaldehyde, and kaempferol were identified in this fraction by HPLC, EI-MS and 1H-NMR. The contents of five main phenolic compounds, p-coumaric, ferulic, vanillic, p-hydroxybenzoic acids and phydroxybenzaldehyde and kaempferol in the soil were found to be 13,382, 3,542, 2,952, 2,164, 1,378 and 990ug per 100g soil, higher than those in the growing soils of Sasa cernua, Picea jezoensis, rice, corn, potato, carrot, soybean and beet, but lower than in the soil beneath red pine. These allelochemicals might have important roles in the distribution of forest species and understory grasses.