Keywords: 
• botany /
• Pinus tabulaeformis /
• Ostryopsis davidiana /
• mixed forest /
• root exudates /
• phenolic acids

Abstract: In order to research the chemical communications in a pure Pinus tabulaeformis forest （PT），an Ostryopsis davidiana forest （OD），and a mixed forest of the two （MPO），the components from rhizosphere soil exudates were analysedusing the gas chromatography-mass spectroscopy （GC/MS） technique. Then，the allelopathic effects of potted P. tabulaeformis seedlings were tested using exogenous phthalic acid and -coumaric acid. Results showed that organic acids comprised most of the detected compounds with PT 63.82%，OD 71.15%，and MPO 69.12%； esters accounted for： PT 8.38%，OD 12.65%，and MPO 14.42%；and phenolic acids were： PT 27.80%，OD 16.30%，and MPO 16.46%. Seven phenolic acids were detected in the 3 forest types： hydrocinnamic acid （not in MPO）； -hydroxybenzoic acid； 4-hydroxybenzeneacetic acid； phthalic acid； 3，4-dihydroxy benzoic acid； 3，5-dihydroxy benzoic acid； and -coumaric acid. For the seven phenolic acids PT more than MPO and except for 3，4-dihydroxy benzoic acid were 2.5 times greater in OD than MPO with -coumaric acid being 8 times greater. For PT seedlings compared with the controls，after treatments of 2.5 mgL-1 phthalic acid，the height increased，and after treatments of 2.5 mgL-1 -coumaric acid，the biomass increased. Also，their allelopathic response index was positive with an increased inhibiting effect as concentrations increased； however，the inhibiting effect of phthalic acid decreased more than -coumaric acid. Thus，a lower content of phenolic acids may be one of the important reasons that mixed forests grew better than two other pure forests.［Ch，2 fig. 1 tab. 12 ref.］