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Effect of freezing and thawing cycles on soil microbial activity and organic carbon density in forest swamp wetland with various drainage afforestation years

GUO Dongnan;ZANG Shuying;ZHAO Guangying;Key Laboratory of Remote Sensing Monitoring of Geographic Environment,College of Heilongjiang Province,Harbin Normal University;  
Taking the wetland soil in the Xiaoxing'an Mountains as the object,changing trends of soil microbial biomass,enzyme activity and organic carbon density in forest swamp wetland with various drainage afforestation years under different freezing and thawing cycles were analyzed. The relation between soil microbial activity and organic carbon density was investigated in order to reveal the soil carbon cycle process in alpine-cold and high latitude regions during the freezing-thawing season. Freezing-thawing cycles has impacted significantly on microbial biomass carbon and nitrogen in soil( P 0. 05). After nine freezing-thawing cycles,microbial biomass carbon and nitrogen in soil decreased obviously,and the shorter the drainage time,the more the decrease in microbial biomass carbon and nitrogen in soil,as showing in three different drainage afforestation wetlands.These reveal that repeated freezing and thawing would result in deeper degree of microbial biomass reduction for a long time. Before and after the freezing and thawing,soil invertase and amylase activities showed a declining trend. Compared to-5 to 5 ℃,-25 to 5 ℃ repetitive freezing-thawing treatment could decrease enzyme activity,which suggested that the larger range of freezing and thawing temperature would accelerate the activity reducing. With the change in number of freezing and thawing cycles and temperature,soil organic carbon density in the four wetlands was stable basically,but still remained positive correlations with microbial biomass and enzyme activity. Therefore,studying the regulating process of soil microbial activity is useful to understand,directly or indirectly,the change trend and verify the essential response mechanism of soil organic carbon density.
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