Studies On The Dynamics Of Soil Microorganisms In A Eucalyptus Plantation

Soil productivity and biodiversity decline is a popular problem in the soil of Eucalyptus plantation. The present study tries to determine the seasonal variation pattern of soil microorganisms, soil biological activity, soil enzyme activity and temperature, rainfall, soil nutrient status in a Eucalyptus ABL12 plantation with different undergrowth, located in Danzhou, western Hainan Province, and the potential allelochemicals in the related soil. It is aimed at getting a full picture of the relationship between soil microorganisms and related ecological and environmental factors, so as to provide some theoretical basis for the development of more desirable Eucalyptus plantations and sustainable management of the land under the Eucalyptus.The results indicated that, the soil microbial properties and soil nutrients of the Eucalyptus stand were lower than those of the controls, the vegetable field and rubber tree stand. Among the three Eucalyptus sample plots, all the parameters measured were recorded higher in the Eucalyptus intercropped with tropical pasture species than the Eucalyptus monoculture, while between the intercropping plots, the legume-intercropped plot was higher than the herbage-intercropped plot. The numbers of soil microorganisms, soil biological activity, soil enzyme activity and soil nutrients were recorded highest in vegetable field, followed at a decreasing order by rubber tree plantation, legume-intercropped plot, herbage-intercropped plot and monoculture plot. All the parameters measured showed a tendency of vertical variation, i.e., decrease with the increase of soil depth. Seasonal variation was also observed in the numbers of soil microorganism, soil biological activity and soil enzyme activity with a single peak curve pattern that occurred in September and October at large. Bacteria were found to be the most abundant, followed by actinomycetes and fungi. GC/MS chromatographic analysis of potential alleochemicals in the soil under the E.ABL12 indicated that the quantity of components from soil under intercropping with legumes were much higher than those from the soil under herbaceous intercrops and monoculture of the Eucalyptus species. Some components identified, such as phenols and terpenes, are well documented as allelochemicals. But their actual relationship with the soil microorganisms awaits further...