Research On Typical Dryland Crops Growing Season And Fertilization On Related Nitrogen Transformation Microbial

Nitrogen is the essential nutritional element for plants and the limited factor for the soil productivity.In agro-ecosystems,nitrogen needed by the crop growth mainly depends on large amounts of chemical nitrogen fertilizer,which may trigger a series of environmental problems and influence the function and stability of the soil ecosystem.Microorganisms are the key players of many soil functions such as biogeochemical cycling.Ammonia-oxidation microbes and nitrogen fixation microbes play key roles in the nitrogen cycle.It is far-reaching to understand and forecast the impacts of fertilizer and environmental changes on soil microorganisms and ecosystem by exploring the response characteristics and the mechanisms of soil nitrogen related microbial community to nitrogen in different stages.Various techniques in moleculer biology have been used,such as polymerase chain reaction?PCR?,real-time quantitative PCR,terminal restriction fragment length polymorphism?T-RFLP?,clone and sequencing,in addition,illumina miseq sequencing.We deeply studied the effects of fertilizer on soil microbial community composition,diversity and function in different stages of three typical upland soils.The possible adaption mechanisms are also proposed.The research contents and main findings of this thesis are described as follows:1.Soil samples were collected from three contrasting soils,that is,black soil from Gongzhuling,Jilin province;fluvo-aquic soil from Xuchang,Henan provice and red soil from Taoyuan,Hunan province in two years,and they were collected in different stages of the maize's growing season.This study investigated the impacts of fertilizer on soil physicochemical property?ammonia-oxidization microbes community composition,diversity and function in three soils among different stages.The results indicate:?1?soil type is the most important factor affect these characters,next are sampling year?sampling dates and fertilizer.?2?The straw has a lingering effect on the loss of effective nitrogen;Black soil has the highest hold capacity for effective nitrogen.?3?Fertilizer can promote AOB growing and the gene abundances of AOB has a significant positive correlation with NO₃^--N.?4?NH₄⁺-N?water content and DOC have a significant influence on AOA community.?5?Fertilizer does not change the dominant population of AOA and AOB,but change the relative abundance of some population.2.This study investigated the impacts of fertilizer on soil nitrogen fixing microorganism composition,diversity and function in three soils among different stages by illumina miseq sequencing.There is a significant difference for the nitrogenase activity,the nitrogen fixing genes abundance and the community structure among the three soils in different stages and the variation is inconsistent.?1?The nitrogenase activity of CK is higher than N and NS in black and fluvo-aquic soil;In red soil is NS>CK>N in 2015 y indicates that straw can inhibit the inhibitory effect of N.?2?N can decrease the nifH gene abundance and NS can increase this gene abundance.?3?There is significant difference among the nitrogen fixing community structure.The community structure of fluvo-aquic soil is more closer with the black soil and they can separate respectively between 2015 y and 2016 y.NH₄⁺-N and NO₃^--N are the factors influencing the nitrogen fixing community structure in black soil and fluvo-aquic soil;H2O?DOC and NH₄⁺-N the factors influencing the nitrogen fixing community structure in red soil.3.Microbial community adapt to the environmental changes under the fertilization by changing the community structure.The dominant population has no changes but adjust the relative proportion of each species to adapt to the changes.4.Two years' fertilization treatment changed the ammonia oxidizing and nitrogen fixing microbial community structure,but has little influence on these genes abundance.Functional redundancy might explain the phenomenon of little changes in the activities of microorganisms despite evident changes in the community structure.In conclusion,this thesis decipher the mechanisms of soil ammonia oxidizing and nitrogen fixing microbial communities in response to different fertilizer and stages by combing many molecular methods.Their distribution characteristics are influnenced by the space and environmental factors,having a clear microbial distribution pattern.This research helps to know the nitrogen transformation related microbial community composition and the relationship between its change and the environment as well as the space variables,aiming to provide scientific basis for adjusting fertilization measures to local conditions.