Vegetable Cultivation Of Microorganisms Nitrogen Fertilizer Soil Ammonia Oxidation And Ammonia Oxidation Of Facilities

Nitrication plays crucial roles in soil nitrogen transformation and global nitrogen cycling. The nitrification process is ubiquitous in soil, lead to mineralization-biological immobilization and denitrification. Autotrophic ammonia oxidation is a rate-limiting and the most basic step of nitrification.This process has the ecological significance in the plant nutrient supply and the global N cycle.The polytunnel greenhouse vegetable land is highly intensive cropping patterns. The inputs of chemical fertilizers, pesticides and other agricultural chemicals are at a high level for a long time. Unreasonable fertilization, in particular, an excess application of nitrogen fertilizer has caused soil acidification and secondary salinization in the polytunnel greenhouse vegetable land, reducing nitrogen use efficiency, and raising the risk of NO3-contamination in groundwater. Summer fallow or planting catch crops can alleviate soil acidification and secondary salinization, reducing N leaching and preventing the NO3-pollutionin groundwater. However, so far, the effect of the dosage of nitrogen fertilizer, the summer fallow and planting catch crops on soil microbial community structure and diversity is unclear. In addition, our knowledge about the effect of dosage of nitrogen fertilizer on the nitrification process and the key micro-organisms harnessing the process is still lacking.The studied soil was sampled from an polytunnel greenhouse vegetable land, which was located in Taihu lake region, Yixing. We studied soil with greenhouse rotate crops of tomato, cucumber and celery. The soil was supplied with traditional dosage of nitrogen fertilizer (870kg ha-1). In our study, we supplied N fertilizers at5levels as compared with the traditional amount:(1)20%reduction (N696);(2)40%reduction (N522);(3)60%reduction (N348);(4)100%reduction (NO);(5) no reduction (N870). In this study, basic soil physicochemical characteristics were measured, phospholipid fatty acid analysis (PLFA) was conducted to investigate soil microbial diversity. Community level physiological profiles (CLPP) was conducted to investigate soil microbial functional diversity. Potential ammonia oxidation was also measured, quantitative polymerase chain reaction (qPCR) of amoA gene was conducted to investigate copies of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). Stable isotope probing was conducted to investigate the contributions and mechanisms of AOB and AOA on nitrogen transformation.Results show that different dosage of nitrogen fertilizer have no significant effect on soil microbial community structure, while high dosage (N696and N870) significantly reduce microbial diversity. Summer fallow or planting catch crops (sweet corn) can relieve soil acidification and secondary salinization, reducing N leaching losses, and improving soil microbial diversity. This is likely because excess NO3-is removed by rainwater leaching during summer fallow and absorbed by catch crops. The soil potential ammonia oxidation rate is the highest under a temperature of30℃and neutral pH, indicating that this condition is the mostly suitable for ammoxidation process. High rates of N fertilization (N696and N870) significantly reduce the soil potential ammonia oxidation rate, as well as the copy numbers of amoA gene of AOA and AOB. The soil potential ammonia oxidation rate of AOB is higher than AOA. Although the amoA gene abundance of AOA is more than AOB, the contribution of AOB in ammonia oxidation may be greater than AOA. N522is more conducive to active AOA than to AOB, moreover, N870is more conducive to the active AOB than AOA. AOB is more suitable for the nitrogen-rich agricultural soil than AOA. There is a significant difference in the community structure and composition of active AOA and AOB in the soil applied with different dosage of nitrogen fertilizer. Seventy-nine percentage of active AOA with NO is clustered to Group1.1a,72percentage for active AOA about N522is clustered to Group1.1b, while nearly100percentage active AOA for traditional N870is clustered to Group1.1a-associated. Almost100percentage of active AOB with NO and88percentage of active AOB with N522are affiliated to Nitrosospira.sp.Nsp65-like group,78percentage of active AOB with N870is affiliated to Nitrosococcus watsonii sp. nov. High rates (N696and N870) of N fertilization lead to high levels of inorganic nitrogen accumulation in the soil, causing soil salinization and acidification. Our results combing with the existing studies show that the treatment of40%reduction (N522) not only maintains soil quality and vegetable production, but also keeps the ammonia-oxidizing microbial activity in the soil. Therefore, we can conclude that in greenhouses the annual application of522kg ha-1nitrogen fertilizer is reasonable. This study provides a theoretical basis for scientific fertilization in the greenhouse soil in China and for improving the efficiency of nitrogen fertilizer.