Allelopathic effects of phenolic acids on the growth and photosynthetic characteristics of Eucalyptus grandis × E. urophylla seedlings

We studied the allelopathic effects of phenolic acids in the Eucalyptus plantations soil on Eucalyptus seedlings growth. Based on the actual content of p-hydroxybenzoic acid, vanillic acid, ferulic acid, coumaric acid, benzoic acid and salicylic acids in soil of Eucalyptus grandis × Eucalyptus urophylla plantations (X), concentration gradients of each phenolic acid (0.5X, 1.0X, 2.0X) were prepared to apply in potted Eucalyptus seedlings. The results showed that each of the 6-phenolic acids significantly (p < 0.05) promoted or inhibited the stomatal conductance, intercellular CO2 concentration, transpiration rate, chlorophyll fluorescence (minimal fluorescence of dark-adapted leaves, maximal fluorescence of dark-adapted leaves, variable fluorescence of dark-adapted leaves, maximum quantum yield of PSII photochemistry). These treatments also influenced the water-use efficiency and growth parameters (height, root biomass, stem biomass, leaf biomass, shoot biomass, total biomass and root/shoot ratio) of Eucalyptus seedlings. Whereas, none of the test phenolic acids affected the ground diameter or net photosynthetic rate of seedlings. This study indicated that further experiments in Eucalyptus plantations are required to find, whether phenolic acids in Eucalyptus plantations soil significantly affected the growth of Eucalyptus trees under natural conditions and how to regulate the phenolic acids contents in forest soil?