Research On Short-term Effects Of Dryland To Paddy Under The Land Consolidation Process On Farmland Soil Environment

Land consolidation is an essential way to improve farmland quality,reduce farmland fragmentation,and optimize farmland grain production capacity.In order to satisfy the ever-increasing requirements for food security and refined management of “to compensate paddy field for paddy filed taken”.The land consolidation of dryland to paddy field has been widely carried out nationwide.However,for the soils that have served as long-term dryland,such a measure will certainly affect the soil ecological stability.A large-scale conversion of dryland to paddy would inevitably alter the local soil environment or even a large area of agricultural land and affect the physicochemical properties and biological processes of the soil.Therefore,it is necessary to study the systematically scientific problem of the change of farmland soil environment during the process of dryland-to-paddy conversion.This study would provide new strategies for promoting land consolidation to the development of whole area consolidation and ecological consolidation,and provide references for improving the regional ecological environment and for sustainable development of cultivated land.In this study,the experimental field simulation,laboratory tests and highthroughput sequencing technology were used to determine the soil bacteria 16 S rRNA and fungal ITS,compare the changes of soil environment between dry land and paddy field,and reveal the composition of soil microbial communities and the interaction network between bacteria and their driving mechanism.Clarify the changes of the soil carbon-nitrogen cycle functional flora and the interaction between microorganisms and the environment,and explore the changes of the soil carbon pool and the environmental driving mechanism of the farmland soil after dryland-to-paddy conversion.The major results were as follows:(1)The soil physicochemical properties changed significantly,and soil microbial community structure and network interaction tended to be simple after the dryland-topaddy consolidation.First,after the dryland-to-paddy consolidation,a significant decrease in the topsoil pH,soil organic matter(SOM),ammonia nitrogen(AN),nitrate nitrogen(NN),available phosphorus(AP)content potassium content,and an increase in soil electrical conductivity(EC)was observed.None of the available potassium(AK)changed significantly.Second,both the abundance and diversity of soil microbial bacteria and fungi decreased during the first growing season of dryland-to-paddy conversion,and the abundance of Actinobacteria,Firmicutes and Olpidiomycota varied greatly.It shows that the soil microbial community has made corresponding changes to adapt the dryland-to-paddy conversion.Third,compared to dry land,the modular structure of interaction network and interspecific relationship of bacteria and fungi communities in paddy soil were simpler,and the network became more instable.A cooperative relationship dominated in the molecular ecological network of bacteria,while a competitive relationship was dominant in the network of fungi.Forth,The change in soil environmental factors,such as pH,EC,SOM and AK,directly affected the soil microbial community structure.Soil environmental factors have become the key factors restricting the development of microorganisms.(2)The community structure and diversity of carbon-fixing bacteria and methaneoxidizing bacteria related to the carbon-nitrogen cycle of farmland soil changed significantly after dryland-to-paddy conversion.First,the number of ammonium oxidizing microorganisms OTU of amoA and amoB decreased slightly after drylandto-paddy conversion,and the OTU numbers of carbon-fixing bacteria and methaneoxidizing bacteria increased significantly.Second,after dryland-to-paddy conversion,the Alpha diversity index of a ammonia-oxidizing microorganisms decreased slightly,and the Alpha diversity index of soil carbon-fixing bacteria and methane-oxidizing bacteria increased significantly.Third,there was no significant change in the composition of ammonia-oxidizing microorganisms in soil after dryland-to-paddy conversion in the short term.However,the relative abundance and rankings of carbonfixing bacteria and methane-oxidizing bacteria genus were significantly different in dryland and paddy field,and most of the dominant species belonged to Proteobacteria.Forth,the soil carbon-nitrogen cycle functional microbial community diversity and community composition structure are significantly related to environmental factors.Changes in pH,EC,NN,and SOM drived by dryland-to-paddy conversion were the main reasons for changes in soil carbon-nitrogen cycle functional flora.(3)Soil carbon flux,soil organic carbon pool and carbon pool management index(CPMI)changed significantly after the dryland-to-paddy conversion.First,the soil carbon flux and temperature of dry land and paddy field are all single peak curve,and the mean value of soil carbon flux in paddy field was higher than that in dry land.The maximum values of soil carbon flux and temperature are about 13:00.The daily variation of soil carbon flux in dry land and paddy field were 21.84% and 15.02% respectively.Second,the dissolved organic carbon(DOC),Microbial biomass carbon(MBC),Easily oxidized organic carbon(EOC),resistant organic carbon(ROC),soil organic carbon(SOC)and CPMI of farmland decreased after the dryland-to-paddy conversion,and the average decrease of soil MBC and SOC were 28.55% and 29.09% respectively.Third,soil temperature and water content were important environmental factors to control soil carbon flux rate.The indexes of soil carbon pool were significantly correlated with a series of soil properties,such as OTU number,pH,EC,SOM,NN,an,etc.soil environmental factors became the key factors restricting soil carbon pool.(4)A large area of dryland-to-paddy conversion may cause the imbalance of soil carbon and nitrogen cycle in the region,and may cause potential ecological risks.Largescale expansion of paddy field may increase the pressure of farmland carbon emissions.In the future,new monitoring system of soil microbial molecular ecological network and real-time monitoring system of soil carbon flux can be introduced to strengthen ecological control.And we should promote the transformation of land consolidation from quantity and capacity-based consolidation to ecological consolidation,so as to achieve sustainable development of cultivated land and slow down global change.There are 56 charts,11 tables and 175 references in this thesis.