Study On The Biological Characteristics Of Surface Soil In Eucalyptus

The biological characteristics of soil represent the physiological and biochemical activity intensity of soil organisms.The activity of soil organisms influences the physicochemical properties of soil,which reflects the soil fertility status of forest land.In this paper,we choose different ages of Eucalyptus plantations within the management cycle,a cutting-blank of Eucalyptus forest,and different mixed modes of Eucalyptus mixed forests as objects,to study the changes of soil nutrient,enzyme activities,as well as the community and diversity of bacterial and fungal in surface.Combined with the data of stand growth,the study aims to understand the effects of forest age change and mixed cultivation on Eucalyptus forest soil,and provide a theoretical basis for the optimization and adjustment of Eucalyptus forest management methods and forest structure.The main results are as follows:(1)There were certain differences in soil nutrients between different ages of Eucalyptus plantations under current management practices,and the organic matter and nitrogen content of the harvested plots are significantly higher than those of Eucalyptus plantations within 1-5 years.In order to adapt fertilization to the growth of Eucalyptus,some adjustment can be taken: it is necessary to increase the amount of nitrogen fertilizer in the second year of plantations for adjusting the rapid growth.In the fourth year,the amount of phosphate fertilizer and potash fertilizer should be increased.In the fifth year,nitrogen fertilizer and potash fertilizer should be added.(2)Among the three Eucalyptus mixed forests,the soil fertility of the Eucalyptus and Acacia mangium mixed forest and the Eucalyptus and Anthocephalus chinensi mixed forest were significantly higher than that of the control pure forest.Soil nutrients in Eucalyptusand Pinus elliottii×P.oaribaea mixed forest had no significant increase,and the contents of nitrogen and available phosphorus were lower than those of the control pure forest.According to the growth of forest stands,Eucalyptus and Acacia mangium is the best mixed mode in the study.(3)There were certain correlations between soil enzyme activities and soil nutrients.Catalase was negatively correlated with soil nutrients,and acid phosphatase activity was significantly positively correlated with soil organic matter,available phosphorus,and available potassium.Urease activity and soil organic matter and nitrogen had significantly positively correlation,than cellulase activity had no significant correlation with soil nutrients.(4)Proteobacteria and Acidobacteria in the surface soil of Eucalyptus forests in this area were the dominant phylums,and the total relative abundance of these two phylums accounted for more than 50% of the total in different areas.Actinomycetes accounted for about 10%(7.53%~13.44%)of the relative abundance of soil bacteria.Acinetobacter,Citrobacter,Candidatus Solibacter,and Rhodoplanes were dominant genuses with a relative abundance of more than 1% in all plots.In addition,certain bacterial groups with high relative abundance belong to family Exiguobacteraceae and Koribacteraceae,but there were no corresponding species annotations.(5)Basidiomycota and ascomycota were the main fungal phylums in the surface soil of Eucalyptus forests in this area,and the total relative abundance of these two phylums was more than 90%.The relative abundance of an unknown fungi group in the cutting plots was significant more than 50%.The superior genuses were Penicillium and Pisolithus in 1,2,3,and 5 year old Eucalyptus plantations,but Clavulina,Penicillium and Scleroderma were predominant in 4 year old plots.There were great difference of fungal dominant genus in mixed plantations.The influence of vegetation on fungal community structure was more significant than that of bacterial community structure.(6)The main ectomycorrhizal fungi in the soil of the Eucalyptus plantation in thestudy area belong to Sclerodermataceae,the main species were Pisolithus marmoratus,Pisolithus albus,Scleroderma citrinum,Scleroderma areolatum,etc.(7)Bacterial diversity was higher than fungal diversity in Eucalyptus soil,and the fungal species is less than 1/3 of that of bacteria.The bacterial and fungal diversity index was positively correlated,among which the Chao 1 index was extremely significant.The predominant bacterial species of the bacteria are basically the same,but there are significant differences in the predominant flora between different fungi.(8)Organic matter,nitrogen,phosphorus,and potassium had great influences on the composition of soil bacterial communities.Organic matter,nitrogen,total phosphorus,pH,and catalase activity had greater impacts on the composition of the fungal community.Bacterial genus with relative abundance over 1% were weakly correlated with soil nutrient and enzyme activity.Hower,Fungi genus with relative abundance greater than 1% had positive correlations with soil nutrient and enzyme activity,and part of the correlations were significant.Soils with better soil fertility had greater numbers of fungi genus which strongly correlated with soil nutrients.