Study On Accumulation Mechanism Of Soil Phenolic Acid In The Pure Eucalyptus Plantation And The Mixed Forest Of The Eucalyptus And Tree Legumes

Phenolic acid is one of important plant secondary metabolism products. In recent years, along with the successive planting productivity decline that pure plantation is growing, the phenolic acid from forest soil arouses the attention from many scholars. Some scholars think that the accumulation of the phenolic acid in earth causes soil degradation, other scholars think the main reason which causes soil degradation is not phenolic acid, on the contrary, some phenolic acid have a protective effect on the plant growth. From the view of recent research results, the research for the phenolic acid in the plants and it effects on the mechanism of plant growth are overall, but the research about the phenolic acid in the soil are relative less, especially it is short of the research about the phenomenon that phenolic acid accumulates in the soil of successive planting forest and mixed forest.This article main research the general characters of the annual changes and their accumulation mechanism of7kinds of acids such as, p-hydroxybenzoic acid, vanillic acid, ferulic acid, coumalic acid, benzoic acid, salicylic acid, cinnamic acid, in the rhizosphere and non-rhizosphere soil which is in the1st and2nd generation of pure Eucalyptus plantation, pure Acacia mangium plantation and the mixed forest of the first generation of Eucalyptus and Acacia mangium and the mixed forest of the second generation of Eucalyptus and Fragrant rosewood. Specific research conclusions are as follows:(1)The continuous planting of second generation of pure Eucalyptus plantation does not cause the phenolic acid accumulates in the soil.The average yearly content of phenolic acid in the rhizosphere and non-rhizosphere soil of the the first generation pure Eucalyptus is respectively33.02μg·g-1and21.41μg·g-1,while the the second generation pure Eucalyptus is respectively24.80μg·g-1and18.29μg·g-1,the first generation pure Eucalyptus is higher than the second,so there is no accumulation of phenolic acid in the rhizosphere and non-rhizosphere soil of the first and second generation pure Eucalyptus.(2)The forest land of pure Eucalyptus plantation is easily formed the allelopathic effect, however, the mixed forest of Eucalyptus plantation can effective reduce the phenolic acid content, reduce the allelopathic effect.The annual average content of phenolic acid in soil of first and second generation of pure Eucalyptus plantation is higher than in rhizosphere soil, the phenolic acid that its root exudates is easily disperse in the forest land, have allelopathic effect on the other species in the forest land. The total annual average content of phenolic acid in non-rhizosphere soil of the mixed forest of the first generation of Eucalyptus and Acacia mangium and the mixed forest of the second generation of Eucalyptus and Fragrant rosewood is respectively10.99μg·g-1and17.25μg·g-1,they are all lower than the same generation pure Eucalyptus plantation.Under the situation of adding exogenous phenolic acids, the desorption of mixed forest land is very low at low concentrations, phenolic acid presents irreversible adsorption state basically, have not allelopathic effect on the other species in the forest, the pure Eucalyptus plantation is on the contrary.The mixed forest of Eucalyptus can effective reduce the phenolic acid content in the forest land, thus, reduce allelopathic effect.(3) The p-hydroxybenzoic acid, Coumalic acid, vanillic acid are the higher content in the soil of pure Eucalyptus plantation and the mixed forest Eucalyptus and Acacia mangium and the mixed forest of Eucalyptus and Fragrant rosewood.The cinnamic acid content is very low in the all forest lands.There are some find during the research of the general characters of the annual changes, the p-hydroxybenzoic acid content always at highest level, thereafter is Coumalic acid, vanillic acid. While the adsorption rate of cinnamic acid is highest in the all forest lands and degradation ability is weakest, it is easily formed retention, but its content is at lowest level, this may cause by decomposition which soil microorganism effect on the exogenous cinnamic acid, the more content cinnamic acid, the more degrading ability.