| Global climate change,including atmospheric nitrogen（N）deposition and precipitation pattern change,will have a huge impact on forest ecosystems.Ammonia oxidizers are widely present in forest ecosystems and play an important role in the global N cycle.Ammonia oxidizers have important ecological functions.Under global climate change,the effects of N deposition and rainfall changes on soil ammonia oxidizers get more attention.Based on the filed platform of simulated N deposition/precipitation enhancement experiment in Jigongshan forest,this paper explores the effects of canopy increased rainfall and N application on soil ammonia oxidizers communities in Jigongshan forest through seven different treatments(control,canopy addition of nitrogen at 25 kg N ha-1 yr-1,canopy addition of nitrogen at 50 kg N ha-1 yr-1,understory addition of nitrogen at 25 kg N ha-1 yr-1,understory addition of nitrogen at 50 kg N ha-1 yr-1,canopy rainfall increase 30%,canopy rainfall increase 30%and nitrogen application 25 kg N ha-1 yr-1).The results show that:（1）At the genus level,from 2013 to 2017,the dominant genus of ammonia-oxidizing bacteria（AOB）community was Nitrosospira under N or rainfall increase treatment.At the genus level,the dominant genus of ammonia-oxidizing archaea（AOA）community included unclassified＿k＿＿norank,unclassified＿k＿＿Nitrosotalea and unclassified＿p＿＿Protcobactcria under N or rainfall enhancement treatment from 2013 to 2017.The abundance percentage of dominant genus in AOA community under long-term N or rainfall enhancement showed the same pattern:unclassified＿k＿＿norank>unclassified＿k＿＿Nitrosotalea>unclassified＿p＿＿Protcobactcria.（2）From a temporal scale perspective,the diversity of AOA community decreased significantly with increasing N application rate,and the richness of AOA community also decreased in the first year of the understory addition of N.However,with increasing time of N application,this inhibition will weaken and eventually stabilize.At the same time,the diversity of AOB community increased with increasing N application rate in the first year of N application,but with increasing time of N application,the diversity of AOB community decreased gradually and was lower than that of the control group.In the first year of canopy rainfall treatment,the diversity of AOA community decreased,then increased slightly,and tended to a dynamic equilibrium state.（3）From a growing season and non-growing season perspective,the diversity of AOA communities after N application in the growing season was higher than that in the non-growing season.In addition,the AOA community richness was high after canopy N and rainfall enhancement treatment in the growing season,and the AOA community richness was high after canopy rainfall enhancement treatment in the non-growing season.The diversity of AOB community in non-growing season was larger than that in growing season after canopy N and rainfall increase treatment.（4）N application treatment significantly reduced soil pH,and N and rainfall enhancement treatment tended to reduce soil pH.N application reduced soil pH,which was the main reason for the differentiation of AOA community structure between N and control plots in August 2015.Rainfall enhancement treatment increased soil pH,which was the main reason for the differentiation of AOA community structure between rainfall enhancement and control plots in November 2017.Rainfall enhancement treatment increased the content of available phosphorus in soil,and then affect the community structure of AOB.It can be seen that the ammonia oxidizers community in the forest of Jigongshan is not only affected by canopy rainfall and nitrogen application,but also by interannual variation,growing season and non-growing season.This study is not only crucial for revealing nutrient cycle in forest ecosystem,but also important for understanding global change influence on soil microorganisms as well as its feedback. |
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