Study On The Diversity And Ammonia Oxidation Of Ammonia Oxidizers In Forest Soils Along An Altitudinal Gradients In Qilian Mountains

Ammonia oxidation,the rate-limiting step of nitrification,is mainly driven by ammonia oxidizing archaea(AOA),ammonia oxidizing bacteria(AOB)and complete ammonia oxidizers(comammox).Ammonia oxidizers play an important role in the ecosystem nitrogen cycling,biodiversity maintenance and ecological function stability.Due to differences in conditions,such as temperature,precipitation and solar radiation,different vertical climatic zones are formed in the mountain environment,making the distribution of organisms present obvious vertical zone spectrum characteristics along altitudinal gradients.Although soil ammonia oxidizing microorganisms have shown being affected by vegetation type and temperature,their distribution patterns and key influencing factors along altitudinal gradients are still unclear,and it also need to be further studied that the response of ammonia oxidizing microorganisms and their functions to temperature changes along altitudinal gradients.In this study,forest soils at different altitudes(2540 m,2717 m,2956 m,3110 m,3300 m)in Pailugou watershed in middle section of the Qilian Mountains were collected,combined with potential ammonia oxidation rate,ammonia oxidation kinetics,physiochemical properties,we studied the activity,abundance,diversity,community structure of ammonia oxidizers and their main driving factors in forest soils at different altitudes with q PCR and high-throughput sequencing.Microcosms were used to study the response of ammonia oxidation rate,abundance,communities and stability of ammonia oxidizers in the forest soils from different altitudes to elevated temperatures.The results of this study provide data support for the altitudinal distribution of ammonia oxidizers and their response to environmental changes,and provide scientific basis for environmental monitoring and ecological restoration.The main results were shown as follows:(1)Soil ammonia oxidation rate was different along the altitudes,and it was significantly lower at 2717 m and 3110 m than at other altitudes.(2)Acetylene addition experiments showed that autotrophic ammonia oxidation was dominant in different altitude soils.Octyne and PTIO addition experiments showed that AOA dominated the ammonia oxidation in different altitude soils.(3)The abundance of AOA amo A gene was significantly higher than that of AOB amo A gene in all samples.The abundance of AOA was mainly affected by altitude,soil moisture and NH₄⁺-N,and AOB was mainly affected by soil NH₄⁺-N and NO₃^--N.(4)The dominant AOA and AOB cluster were Group I.1b and Nitrosospira,respectively.Soil p H,moisture and SOC were the main environmental factors affecting the diversity and composition of AOA and AOB community in various altitude soils.(5)The abundance and diversity of comammox were significantly higher than those of AOA and AOB.The dominant cluster of comammox Nitrospira was Clade B.Soil p H,moisture and SOC were the main environmental factors affecting the abundance,diversity and community structure of comammox Nitrospira.(6)Soil ammonia oxidation rate increased with short-term elevated temperatures.The ratios of AOA to AOB abundance increased in low-altitude soils,but decreased in high-altitude soils with elevated temperatures.The abundance of comammox Nitrospira first decreased and then increased in low-altitude soils with elevated temperature,while it decreased in high-altitude soils,but had no significant change.(7)The response of ammonia oxidizers in low-altitude and high-altitude soils to elevated temperatures was different.At 25?,the stability of comammox was higher than that of AOA and AOB in all altitude soils.The stability of AOB was relatively higher in low-altitude soils,while that of AOA was higher in high-altitude soils.