Effects Of Freeze-thaw Processes On The Organic Carbon Composition And Organic Carbon Mineralization In Plough Layer Of Black Soil

The black soil resource in Northeast China is an important soil resource in China,the content of organic carbon is high.However,there is about half a year of freeze-thaw alternation in Northeast China,which affects the organic carbon in the black soil.Based on the topsoil soils in the typical black soil area as the study subjects,using the method of indoor simulation of freezing and thawing,study the freezing and thawing cycles(0,3,6,9,12 times)the soil water content(natural moisture content,saturation water content)and freezing temperature(-5?,-15?,-25?)effects on soil organic carbon active components,stability components and organic carbon mineralization,analysis their change rule,it provides theoretical basis for soil organic carbon fixation,carbon reservoir balance,soil fertility conservation and greenhouse gas emission reduction in black soil cultivation.The results showed that the effect of freeze-thawing alternating action on total organic carbon of black soil was not obvious,but effects on the content of active organic carbon in black soil was significant.Less freeze-thawing increases the contents of microbial biomass carbon,particulate organic carbon,dissolved organic carbon and light faction organic carbon,but decreased with the increase of freeze-thaw cycles.With the increase of freeze-thaw cycles,the content of readily oxidizable organic carbon in black soil appear an upward trend,while the content of particulate organic carbon appear an downward trend.The active organic carbon was significantly affected by the water content.The effect of soil water content on the stability of organic carbon showed that saturated water content was higher than natural water content,and the response of microbial biomass carbon to soil water content was not obvious.Freezing temperature also had a significant effect on the content of active organic carbon in black soil,treatments under-15? and-25? can increase the content of active organic carbon fractions on a different level.Freezing and thawing can affect the content of organic carbon stability component in black soil.With the increase of freeze-thaw cycles,the calcium bonded organic carbon increases first and then decreases,but the difference is not significant.The iron-aluminum bonded organic carbon and the heavy faction organic carbon displayed a decreasing tendency,while the residual organic carbon had no obvious change.The effect of soil water content on the stability component of organic carbon was that the saturated water content treatment was higher than the natural moisture content treatment.The effect of freezing temperature on the stability component of organic carbon had no obvious regularity,but the difference analysis results showed that the effect of freezing temperature on iron-aluminum bonded organic carbon,calcium bonded organic carbon and residual organic carbon has reached a significant level.Freezing and thawing also affected the mineralization of soil organic carbon.During the 35 days of indoor cultivate,compared with the control soil without freeze-thaw cycle treatment,the mineralization rate and accumulated mineralization amount of organic carbon in frozen and thawed soil were higher than those in control.Under freezing and thawing treatment soil organic carbon mineralization rate all showed priming effect on the first day of indoor cultivate,but with the increase of freeze-thaw cycles,the rate of organic carbon mineralization and cumulative mineralization amount has no obvious regularity.The decrease of freezing temperature promoted soil organic carbon mineralization,especially freezing temperature treat at-25?,the amount of soil organic carbon mineralization,cumulative mineralization amount and mineralization intensity were significantly higher than that of the control treatment.Soil water content can also affect the mineralization of soil organic carbon.Under saturated water content conditions,the amount of mineralization,cumulative mineralization amount and mineralization intensity of organic carbon are significantly higher than natural water content.