Greenhouse Gas Emission And Accumulation Of Amino Sugar In Black Soil Under Freeze-thaw Cycles

The freezing and thawing action can affect the microbial activities through changing the soil structure and hydrothermal conditions,which leads to significantly affect the decomposition and accumulation of soil organic matter.The black soils in Northeast China have been stressed by freezing and thawing action in the late of autumn and the beginning of spring.However,the microbial process on the mineralization of soil organic matter?SOM?affected by the freezing and thawing has little been known.Straw and manure,as important carbon sources,can affect the metabolism of soil microorganisms,thus affecting the decomposition and transformation of SOM in the black soils.This study was carried out under different intensities and numbers of freezing and thawing alternation using indoor simulation method with molisol soil in Northeast of China,to monitor the effects of freeze-thaw on N₂O and CO₂ emissions and the dynamics of amino sugar during the incubation,and discuss the response with the addition of different exogenous carbon.The following two treatments were selected:1)mineral fertilization?NPK?;2)manure with mineral fertilization?NPKM?.In order to examine the effect of microbiological transformation process of soil carbon and nitrogen,and also provide a theoretical basis for the returning of crop residue.The main results were:?1?Freeze-thaw effect significantly influences the decomposition of soil organic matter,and also was differed in different soil fertility level.Freeze-thaw effect can significantly reduce the emission rate of greenhouse gas for NPK treatment,and increased CO₂ emission rate for NPKM treatment,and significantly increased with increasing freeze-thaw intensity.Substrate addition?manure and straw?significantly increased the instantaneous emission rate of CO₂ gas compared to control soil.Under 5/-4?freezing and thawing,the addition of substrate significantly increased the N₂O gas emission rate for NPKM treatment.Under the5/-9?freeze-thaw effect,the addition of substrate had no significant effect on the N₂O emission for both NPK and NPKM treatments.?2?Freeze-thaw affected soil amino sugar synthesis and accumulation.Under freezing and thawing,no significant different was found between NPK and NPKM treatment of the CO₂ instantaneous rate.Under 5/-4?freezing-thawing,the proportion of amino sugars in NPK was significantly higher than that of NPKM treatment.Under 5/-9?freezing and thawing,there was no significant difference for the ratio of organic matter utilized by microorganisms between the two treatments.5/-9?freezing and thawing significantly reduced the synthesis and decomposition of organic matter with the addition of straw residue and reduced the activity of the microorganisms compared with the constant temperature incubation for NPK treatment.For NPKM treatment,freezing/thawing at 5/-4?enhances the decomposition and mineralization of organic matter by microorganisms as compared with constant temperature incubation,it also significantly reduced the synthesis and utilization of organic matter by microorganisms.?3?Freeze-thaw affected the accumulation of cell residues from different microorganisms in the soil.Compared with the constant temperature incubation,5/-9?freezing-thawing significantly reduced the accumulation of fungal residue in the soil with the addition of straw for NPK treatment.5/-4?significantly reduced the accumulation of fungal residues in soils for NPKM and NPKM+organic fertilizers.Compared with control soil,the addition of substrate under freeze-thaw cycle significantly increased the accumulation of bacterial residues in NPK soil.The ratio of glucosamine to muramic acid in NPK treatment was significantly greater than that in NPKM treatment,indicating that the microbial community structure and metabolic function varied in different fertilization soils,the accumulation of fungal residues in NPK treatment was significantly higher than that of bacterial residues compared with NPKM treatment.In summary,freeze-thaw effects significantly affect the process of decomposition and transformation of soil organic matter,and the decomposition rate and transformation differed in different fertilization treatments,and the response to exogenous substrates is not consistent all the time.Futher study needs to combine the isotope tracing techniques and separates microbial metabolic components to study the microbial process of decomposition and transformation of organic matter in different fertilization soils under freeze-thaw cycles.