Characteristics Of Soil Water-soluble Organic Carbon And Nitrogen And Microbial Biomass Carbon,Nitrogen In Continuous Planting Eucalyptus Plantation

Nitrogen and carbon are essential nutrients for plant growth and development,and play an important role in the formation of forest ecosystem and the multiply and replacement of forest communities.In this research,the soil microbial biomass carbon ang nitrogen,soil water-soluble organic carbon and nitrogen and their correlation in Eucalyptus plantation of different generations(the first,second,third and four)were studied by using space instead of time method.The purpose of the research was to clarify the influence of soil microbial biomass carbon and nitrogen,soil water-soluble organic carbon and nitrogen in continuous planted Eucalyptus plantation.Further,this also revealed the evolution of Eucalyptus forest soil fertility and to provide the scientific basis for sustainable management of Eucalyptus plantation.The main results were as follows:(1)In the 0?20 cm soil layer,the change of mean annual soil water-soluble organic carbon contents were I generation(36.32 mg·kg-1)>?generation(31.68 mg·kg-1)>? generation(30.48 mg·kg-1)>? generation(29.04 mg·kg-1).With the increase of planting generation,the tendency of soil water-soluble organic carbon content decrease.As the change of seasons,soil water-soluble organic carbon contents and the percentage of the total organic carbon was high in the cold season and the warm season was low.The difference of percentage of four planting generations were significant(p<0.05).(2)In the 0?20 cm soil layer,the change of mean annual soil water-soluble organic nitrogen contents were I generation(3.17 mg·kg-1)>?generation(3.11 mg·kg-1)>? generation(2.94 mg·kg-1)>? generation(2.70 mg·kg-1),namely with the increase of planting generation,soil water-soluble organic nitrogen content decreases.As the change of seasons,the contents of water-soluble organic nitrogen were low in cold season and high in warm season.(3)In the 0?20 cm soil layer,the change of mean annual soil microbial biomass carbon contents were I generation(249.67 mg·kg-1)>? generation(225.06 mg·kg-1)>? generation(198.94 mg·kg-1)>? generation(183.86 mg·kg-1).With the increase of plant generation,soil microbial carbon contents had a tendency to reduce.The seasonal variation rule is high in the cold season and the warm season is low.There was a significant difference between spring and autumn(p<0.05).The percentage of soil microbial biomass carbon in total organic carbon was low in cold season and high in warm season.(4)In the 0?20 cm soil layer,the mean annual soil microbial biomass nitrogen contents were I generation(28.19 mg·kg-1)>? generation(27.72 mg·kg-1)>? generation(24.83 mg·kg-1)>? generation(20.67 mg·kg-1).Its seasonal variation was similar to that of soil microbial biomass.However,the difference between different generation in the same season were significant(p<0.05).(5)Correlation analysis showed that there were close positive correlation between soil water-soluble organic carbon,nitrogen and microbial biomass carbon and nitrogen of Eucalyptus plantation,them and the soil pH and soil total organic carbon,total nitrogen have a close correlation.To sum up,even of Eucalyptus plantation continuous planting causes soil total organic carbon and total nitrogen content tends to decrease,but also lead to soil microbial biomass carbon,nitrogen and water-soluble organic carbon and nitrogen content showed a trend of gradual decline.