The Identification Of Water Soluble Phenolic Allelochemicals Of Eucalyptus Grandis Plantation And Their Physiological And Ecological Effects On Plants

Allelopathy were controversial underlying the ecological matters associated with Eucalyptus.Water soluble phenolic compounds characterized by higher solubility and salinity,are easily to enter into soil,thus showing stronger allelopathic effects.In present,the studies about the allelopathy of Eucalyptus are focused on physiological effects of organ and soil water extracts on plants,which is hard to reveal the ecological mechanisms of release and active expression of allelochemicals of Eucalyptus affecting by management measures and environment factors.Accordingly,based on across a range of Eucalyptus grandis plantations,the objective of this study were to screen major phenolic compounds of E.grandis to reveal the physiological effects of major phenolic compounds on plants.Furthermore,the density control experiments were to reveal the ecological factors that affected the allelopathic effects of phenolic compounds.The results showed that:1)A total of 17 phenolic compounds including seven phenolic acids and 10 flavonoids were confirmed.The concentrations of phenolic compounds varied in leaf litter,root and rhizosphere soil and varied with forest ages.The concentrations of phenolic compounds in leaf litter and root were higher than rhizosphere soil.The majority of phenolic acids and some of flavones in leaf litter and root from E.grandis were abundant in before rotation periods.In rhizosphere soil,except for Hydroxyphenyllactic acid and Angoletin,the concentrations of other phenolic compounds of E.grandis showed no significant changes with forest ages.Four and eight-year-old plantations were the critical turning points for the concentrations of phenolic compounds released from E.grandis.The result of Canonical correspondence analysis(CCA)showed that the concentrations of phenolic compounds in leaf litter and root of E.grandis were more influenced by forest ages,soil water content,soil bulk density,soil organic matter and Shannon-Wiener index of plant,s.However,the concentrations of chemicals in rhizosphere soil of E.grandis were not significantly influenced by the changes of the environmental factors across a range of plantation ages.2)Three chemicals had effects on seed germination,seedling growth and physiological indexes of target plants.At the lowest dose of 6-Methylsalicylic acid,the germination rate of V.radiate were stimulated.Aside from this,all of the three chemicals at various concentrations had inhibitory effects on three tested plants.The shoot length,radicle length and shoot/radicle mass ratio of three tested plants were stimulated at lower doses of three phenolic acids,but were inhibited at higher doses.The effects of three phenolic acids on SOD,POD and CAT activities of tested plants were stimulated at lower doses,but inhibited at higher doses and this inhibition effects were strengthened with increasing concentrations.The soluble protein content in three tested plants in the salicylic treatments and V.radiate in the 6-Methylsalicylic acid and 4-Hydroxybenzoic acid treatments were promoted at lower doses and reduced at higher doses.The soluble sugar content in three target plants in 6-Methylsalicylic acid treatments were promoted at lower doses and reduced at higher doses.Aside from this,the other treatments stimulated the soluble protein and soluble sugar content of three tested plants at all concentrations.Under three phenolic acids treatments,the prolin content of three target plants were stimulated at all concentrations.The effects of three chemicals on MDA content of three target plants were inhibited at lower doses,but were stimulated at higher doses.The root activities of three tested plants were promoted at lower doses,but were inhibited at higher doses.3)Comparing the identification result of phenolic compounds of E.grandis in a chrosequence to various densities,the common substance were salicylic acid,4-Hydroxybenzoic acid,gallic acid,chrysin,epicatechin.The concentrations of chrysin in four years old E.grandis and gallic acid and epicatechin in eight years old E.grandis were more higher in higher forest densities.However,the concentrations of 4-Hydroxybenzoic acid in four years old E.grandis and salicylic acid and chrysin were more higher in lower forest densities.In four and eight years old E.grandis with different densities,Myrsine Africana,Camellia oleiferaAbel and Ficus henryi Warb were the dominant shrubs,Dicranopteris dichotoma and Alternanthera philoxeroides were the dominant herbages,Cyperus difformis,Centellaasiatica,Oxalis rubra and Oxalis corniculata were common herbages.The plant species of four and eight years old E.grandis were increased with decreasing densities.The plant species of eight years old were higher than that in four years old.The result of CCA showed that salicylic acid,4-Hydroxybenzoic acid,gallic acid were more influenced by forest ages,forest densities,pH,soil water content,soil bulk density and plant,s Shannon-Wiener indexes.In summary,the major phenolic compounds of E.grandis include salicylic acid,6-Methylsalicylic acid and 4-Hydroxybenzoic acid.Salicylic acid and 4-Hydroxybenzoic acid had the stronger allelopathic effect,and the concentrations of which changed significantly with forest ages.They had the significant effects on the seed germination,seedling growth and physicological indexes of tested plants and this effect had concentration effects.Phenolic compounds secreated by E.grandis were affected by environmental factors such as forest ages,forest densities,pH,water content,soil bulk density and plant,s Shannon-Wiener indexes caused by density management measures.