Effects And Mechanisms Of Peatland Reclamation On Soil Nitrogen Mineralization

Due to the long-term or seasonal flooded environment,with small number and weak activity aerobic microbe,slow decomposition of animal and plant residues,the decomposition rate of organic matter in peatland is less than the accumulation rate,so the organic matter contents of peatland is high.In the 1950s,in order to solve the food crisis caused by population growth,peatland were reclaimed more than 1×10⁸ hm² in China,and northeast of China contributes most to the reclamation.Agriculture activity has significantly reduced the content of soil total nitrogen and organic matter,and the mineralization is the link of soil nitrogen release.With the development of peatland reclamation,changes in hydrological conditions,sediment input and physical and chemical properties of soil will lead to soil nitrogen mineralizaton change.Mineralization is also the most typical process of peatland degradation.But the process and mechanism of the effect of peatland reclamation on soil nitrogen mineralization are still unclear,especially the study on the correlation between minralization and microbe.This study was carried out in the Longwan National Nature Reserve,which is typical peatland of Changbai Montain in northern China.The study focuses on the process change and influencing factors of mineralization.The effects of agricultural reclamation on soil environmental factors,physical and chemical properties and soil enzyme activities were studied through field investigation and sampling.The effects of reclamation on soil microbial community structure were analyzed by high-throughput sequencing and qPCR technology,and the intensity of soil mineralization was measured by in-situ cultivation.Analyze the relationship among soil physical and chemical properties,microbial community structure and soil mineralization.To reveal the degradation process and mechanism of peatland and provide scientific basis for ecological conservation and restoration measures such as returning farmland to wetland.The main conclusions are as follows:（1）Agricultural reclamation significantly changed the soil physical and chemical properties and soil environment of peatland,and then affected the content of various forms of nitrogen in the soil.Specifically,reclamation significantly increased soil bulk density,soil clay and silt content,and decreased soil sand content.Reclamation reduced soil organic matter（SOM）,organic carbon（SOC）,total nitrogen（TN）,carbon nitrogen ratio（C/N）,dissolved total nitrogen（DSN）,dissolved organic nitrogen（DON）and particulate organic nitrogen（PON）.Among them,reclamation reduced soil TN content by 13.36%and 67.86%respectively in rice field and dry field,and decreased PON content from 12.88 g/kg to 7.62 g/kg and 1.78 g/kg.In addition to fertilization season,agricultural reclamation reduced soil microbial biomass nitrogen（MBN）and dissolved inorganic nitrogen（DIN）content.The soil pH,OPR and TP could be increased by reclamation.The TP content of corn field was 3.96 times of that of peat swamp wetland.In the process of peatland reclamation,environmental factors and physical and chemical properties of soil significantly affect the content of nitrogen in all forms of soil.Reclamation reduces the impact of environmental factors（temperature,moisture content）and physical and chemical properties of soil（pH,OPR）on the content of nitrogen in all forms of soil,increases the content of nutrients（SOC,TP）and the interaction of nitrogen in all forms.（2）Agricultural reclamation significantly changed the structure of soil bacterial community and increased the diversity of soil microbial community.The Shannon index showed:paddy field>corn field>peatland.Agricultural Reclamation significantly increased the relative abundances of Actinobacteria,Gemmatimonadetes,Pathesibacteria,and significantly reduced the relative abundances of Blanctomycetes,Firmicutes,Nitrospirea,and Spirochetes.Among them,the difference of relative abundance of Actinobacteria is the most significant,with the increase of 4.99%and22.09%for different reclamation methods.SOC,OPR and TN are the main factors that cause significant differences in bacterial community composition.The effects of agricultural reclamation on the related functional genes of soil mineralization process are as follows:the reclamation of corn field reduces the content of soil apr,and the reclamation increases the absolute abundance of AOA-amoA,AOB-amoA and nxrA.The content of AOB-amo A was higher in peatland and rice field,and the absolute abundance of AOB-amoA was lower in corn field.In the process of reclamation,PON,TN,OPR and pH lead to the difference of functional gene content.（3）Agricultural reclamation and seasonal changes significantly affected the soil nitrogen mineralization,and reclamation would reduce the soil ammonification rate.Reclamation of corn field reduced the soil ammonification rate from 1.12 mgN/kg/d to 0.02 mgN/kg/d.Reclamation can increase soil nitrification rate and promote the total nitrogen mineralization.The average annual nitrification rate increased from-0.46 mgN/kg/d to 0.34 mgN/kg/d and 1.99 mg N/kg/d D in rice and corn fields.The mineralization rate of soil in August increased from-1.14 mgN/kg/d to 1.51mgN/kg/d and 2.41 mgN/kg/d with different reclamation methods.With the seasonal change,the ammoniation rate first increased,reached the maximum in June,then decreased,while the ammoniation rate of corn field showed the opposite trend.The nitrification rate of the three soils increased first and then decreased,and the peak value of mineralization of the three soils appeared in June.（4）The change of moisture content,plant biomass,soil physical properties,OPR,SOM,SOC,TN,TP,DIN,MBN,DSN and PON in the reclamation process results in the change of ammoniation rate.The change of temperature,soil moisture content,physical properties,pH,OPR,SOM,SOC,TN,TP,C/N,DSN,don and PON results in the change of nitrification rate.The changes of soil temperature,plant biomass,physical properties,pH,OPR,TN,TP,NH₄⁺-N,DON and PON are related to the change of mineralization rate.Reclamation reduced the correlation between soil mineralization rate and water content,soil pH,OPR,and increased the correlation between soil temperature,SOC,SOM,TN and various nitrogen components and mineralization rate.（5）The results showed that nitrification rate was positively correlated with AOB-amoA,apr and AOA-amoA,and nxrA was positively correlated with mineralization rate and ammonification rate.The results of nitrogen mineralization path analysis showed that the soil mineralization was limited by AOA-amoA and nxrA in peatland,in rice field mineralization was limited by nxrA and apr limited this process in corn field.