Based on the wetland in the Sanjiang Ecology Station of Chinese Academy of Sciences

the characteristics of soil enzyme activity and fertility under different types of land use

including wetland ecosystem

dryland ecosystem

conversion from dryland to wetland

conversion from dryland to forestland

were investigated.The results showed that there was great significance between the soil enzyme activity(invertase

urease

phosphatase

and catalase)

the contents of organic carbon and soil nutrients under different types of land use

they were the highest in the unreclaimed wetland

20 years after the wetland was reclaimed

the enzyme activity

the contents of organic carbon and soil nutrients all declined greatly than that in wetland

when the reclaimed dryland was recovered to wetland

the enzyme activity

the contents of organic carbon and soil nutrients increased significantly than that in dryland

however

when the reclaimed dryland was recovered to forestland

the contents of all above components were also increased at a different extent than that in dryland.Therefore

it is imperative under the situation to recover the wetland from dryland so as to keep high soil fertility and biological activity

and to maintain the stability of organic carbon in the wetland of Sanjiang plain.