Root exudate constituents and allelopathic effects from forests of Pinus tabulaeformis,Ostryopsis davidiana,and a mixed forest
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 pcoumaric 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); ρ-hydroxybenzoic acid; 4-hydroxybenzeneacetic acid; phthalic acid; 3, 4-dihydroxy benzoic acid; 3, 5-dihydroxy benzoic acid; and p-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 ρ-coumaric acid being 8 times greater.For PT seedlings compared with the controls, after treatments of 2.5 mg·L-1 phthalic acid, the height increased, and after treatments of 2.5 mg·L1 ρ-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 ρ-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.
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