Effects of Freezing and Thawing on Dissolved Organic Carbon and Nitrogen Pool and Nitrogen Mineralization in Typical Wetland Soils From Sanjiang Plain,Heilongjiang,China

Contents of dissolved organic carbon and nitrogen (DOC and DON) and nitrogen mineralization of wetland soils different in freezing and thawing cycle were investigated through an indoor incubation experiment. Results show that with the number of the cycles increasing,DOC and DON rose up first and then declined. DOC peaked after one cycle,either -5 to 5 ℃ or -25 to 5 ℃,while DON did after two cycles of -5 to 5 ℃ and four cycles of -25 to 5 ℃,which indicates that the effect of freezing and thawing alternation within a short time period was significant on DOC and DON in the soil. It was also quite obvious that nitrogen mineralization in the wetland soil was affected by freezing temperature and number of freezing and thawing cycles,and the soils under cycles of -25 to 5 ℃ were higher than under cycles of -5 to 5 ℃ in accumulative nitrogen mineralization. Alternation of freezing and thawing accelerated soil nitrogen mineralization,which facilitated accumulation of soil available nitrogen,thus building up an adequate N pool to meet the demand for N of the plant growing in the spring,which contributes significantly to maintenance of stability of the wetland ecosystem.