Effects Of Long-term Fertilization On Community Structure Of Nitrite-oxidizing Bacteria

Nitrification plays an important role in the process of nitrogen?N?cycling in the biogeochemical circulation in agricultural soils.This process can be divided into the oxidation of ammonium to nitrite mediated by ammonia-oxidizing microorganisms?AOM?,and the oxidation of nitrite to nitrate mediated by nitrite-oxidizing bacteria?NOB?.Because of the importance of ammonia oxidation process,researchers have long focused on the significance of AOM,but relatively ignored the importance of NOB in the N-cycling.Long-term application of fertilizers and straw returning to the agricultural field is one of the dominant agricultural practices to improve crop yield,however,its effect on the function and community structure of the soil nitrite-oxidizing microorganisms has not been reported yet.In addition,as the key component of soil structure,soil aggregates with different sizes provide spatially heterogeneity,and studying the function and community composition of NOB in soil aggregates will help us to further reveal the microbial ecological mechanism of N-cycling regulation in microscale environment.Based on the long-term experiment with diverse fertilization treatments?CK,M,NPK and MNPK?under wheat-maize rotation system?Qiyang Red Soil Research Station in Hunan Province?and the long-term experiment of straw returning treatment in rice-rape rotation system?Wuxue Straw Returning Research Station in Hubei Province?,we investigated the response of NOB function and community composition to diverse fertilization treatments and straw returning treatment,the effect of soil variables on composition of nitrite-oxidizing microbial communities,the relationship between the variation of nitrite-oxidizing bacteria communities and their functions,the influence of soil aggregates under different fertilization treatments on the diversity and community structure of nitrite-oxidizing bacteria,by using the modern molecular ecology technology including Illumina Mi Seq sequencing and Quantitative Real-time PCR?q PCR?.The mian findings were as follows:Effects of diverse fertilization treatments on nitrite-oxidizing microorganisms in a typical acid red soil under wheat-maize rotation system.Long-term application of fertilizer can significantly increase soil carbon and nitrogen content.Long-term different fertilization treatments can significantly affect the soil potential nitrite oxidation activity?PNO?;the PNO was lowest in the CK treatment(0.07?g NO₂^--N kg^-1dry soil h^-1)and highest in the M fertilizer treatment(0.37?g NO₂^--N kg^-1dry soil h^-1).Long-term fertilization treatment can significantly affect the abundance of Nitrobacter and Nitrospira;M and MNPK fertilizer can improve the Nitrobacter abundance,while NPK fertilizer can reduce the Nitrobacter abundance.For Nitrospira,fertilizations can reduce its abundance to varying degrees.The community structure of Nitrobacter-and Nitrospira-like NOB was significantly affected by fertilization types.This maybe due to the different survival strategy,Nitrobacter are defined as K-strategist which preference for high substrate result from fertilizer;while Nitrospira are characterized as r-strategists,which like low substrate environment.Soil p H was the major factor influencing the community composition of Nitrobacter-and Nitrospira-like NOB.The variations of the community structure of Nitrobacter-and Nitrospira-like NOB can significantly impact the soil PNO.Our data suggested that the abundance and community structure of Nitrobacter play more key roles in regulating the PNO through the fertilizer.Organic fertilizers are beneficial to increase the soil PNO,thereby providing sufficient NO₃^-for wheat growth,and can provide theoretical guidance for agricultural fertilization.Effects of different fertilizer types on nitrite-oxidizing microbial community structure in soil sggregates under wheat-maize rotation system.Soil aggregates are separated as larger-aggregate?>2000?m?,macroaggregate?2000-250?m?,microaggregate?250-53?m?and silt+clay?<53?m?.Long-term fertilization makes the soil properties of carbon,nitrogen,phosphorus and potassium contents present the patterns of macroaggregates?microaggregates>silt+clay across the soil aggregates scale.Moreover,three fertilization treatments can significantly increase the soil carbon,nitrogen,phosphorus and potassium contents?except ammonium?.Nitrite-oxidizing bacterial community composition and diversity are influenced by fertilizer regimes,but are independent of the soil aggregate in this soil.Soil available phosphorus and ammonium contents are the most important driving factors on Nitrobacter-and Nitrospira-like NOB alpha-diversity.In addition,soil variables?e.g.,soil carbon and nitrogen?can significantly affect the community structure of Nitrobacter-and Nitrospira-like NOB.Therefore,soil nutrient availability,which depends on the elements supplied by the fertilizers,is central to the formation of the NOB community's structure.Effects of straw returning on nitrite-oxidizing microbial community diversity under a rice-rape rotation system.Straw returning treatment can significantly inhibit the soil PNO before rice planting,while the soil PNO has no significant difference between straw returning treatment and non-returning treatment after rice planting.Both straw returning and rice planting stage significantly affect the abundance and community structure of Nitrospira-like NOB in soil,while not the Nitrobacter-like NOB.This indicated that Nitrobacter may have stronger environmental resistance,and the organic matter produced by the decomposition of straw may inhibit Nitrospira abundance in flooded ecosystems.Soil p H,moisture,ammonium,total phosphorus and total potassium content are the main environmental factors controlling the variation of community structure of Nitrospira-like NOB.The abundance of Nitrospira-like NOB is much higher than that of Nitrobacter-like NOB,and the Nitrospira abundance rather than Nitrobacter can better regulate the soil PNO,indicating that Nitrospira-like NOB may play a key role in this soil.The results of this study on the effects of fertilization treatment and straw returning on the function and community variation of NOB can be used to further understand the nitrogen cycle,formulate reasonable fertilization measures,maintain soil structure,improve soil fertility,and improve field production environment provide scientific guidance.