Water-soluble phenolic acids in soil under silver fir forests

The biological activity of solutions extracted from different forest soils (Calcaric Phaeozem, Haplic Phaeozem, Chromic Luvisols and Dystric Spodic Cambisols) located in a single climatic area covered by silver fir (Abies alba Mill.) and beech (Fagus sylvatica L.) forests was investigated. The presence of phenolic acids in the soil solution varied in the different soils and their total concentration ranged from 65.7 μM in the Dystric Spodic Cambisols to 154 μM in the Calcaric Phaeozem depending on the dissolved organic matter. The phenolic compounds identified were: gallic, pyrogallic, protocatechuic, gentisic, phthalic, syringic, p-hydroxybenzoic, vanillic, caffeic, pcoumaric and ferulic acids. Their hormone-like activity is discussed: gallic and protocatechuic acids showed an auxin-like activity while pyrogallic, gentisic, phydroxybenzoic, vanillic, ferulic and syringic acids exhibited a gibberellin-like activity.