| Serious air pollution events have frequently occurred in China associated with the acceleration of urbanization and industrialization in recent years.As an important central city in western China,Xi'an has been increasingly polluted and the pollution has seriously affected people's lives and health.In order to analyze the microbial distribution characteristics of atmospheric particulates in Xi'an,this study set up three sampling points in Xi'an from February2018 to January 2019:Chang'an University Weishui Stie?suburb?,Chang'an University Yanta Site?urban?,Qinling Taiyi Site in Chang'an District?mountain area?,using air particulate sampler?ZR-3930?to collect particles of different particle sizes(PM10 and PM2.5),then analyzing the microbial concentration and bacterial community structure in atmospheric particulates by fluorescence microscopy and high-throughput gene sequencing.In addition,the study also explored the effect of environmental factors on the distribution of microbes in the atmosphere.The main findings are as follows:?1?There was a slight difference in microbial concentration between PM10 and PM2.5during the period of sampling.The concentration of microbial concentration in PM10 ranged from 0.3228×105cells/m3 to 2.1417×105cells/m3,with the mean value of 1.0225×105cells/m3;The concentration of microbial concentration in PM2.5 varied from 0.5053×105cells/m3 to1.1175×105cells/m3,with the mean value of 0.6974×105cells/m3,and the concentration of microorganisms in PM10 is slightly higher than PM2.5.?2?There were seasonal differences in microbial concentration distribution in PM10 and PM2.5.The highest value of microbial concentration on PM10 and PM2.5 appears in In November,the lowest value appeared in July.The microbial concentration in autumn and winter was higher,while the microbial concentration in summer was the lowest.The results of multivariate stepwise regression analysis showed that the distribution of atmospheric microbial concentration was affected by meteorological factors and environmental factors.?3?The microbial concentration and particulate matter concentration under different particle sizes in haze days were higher than that in clean days.As the pollution level deepened,the concentration of particulate matter increased,and the microbial concentration firstly increased and then decreased,and the maximum value appeared under moderately polluted,while the maximum microbial concentration appeared under lightly polluted.?4?Analysis of the spatial variation of microbial concentration in PM10 and PM2.5 showed that the microbial concentration in the mountain area was the highest?0.8640×105cells/m3 and0.6792×105cells/m3?,followed bytheurbanregion?0.7580×105cells/m3 and0.6371×105cells/m3?,themicrobialconcentrationinsuburbisthelowest?0.6812×105cells/m3and 0.5323×105cell/m3?.In addition,by analyzing the seasonal variation characteristics of microbial concentration on PM10 and PM2.5 at different sampling points,it was found that the order of seasonal variation of microbial concentration in PM10 and PM2.5 in the atmospheric environment of suburb and mountain area were:autumn>summer>winter,and the seasonal variation of microbial concentration in PM10 and PM2.5 at urban was:autumn>winter>summer.?5?The correlation of various environmental factors indicated that different environmental factors have different effects on microbial concentration.Through principal component regression analysis,it was found that suburb and urban area were mainly affected by environmental factors(PM2.5,PM10,O3,NO2,SO2),the mountain area was mainly affected by meteorological factors?temperature,humidity,wind speed?.?6?The time-variation characteristics of bacterial community structure in PM10 and PM2.5in Xi'an City were analyzed.It was found that the composition of bacterial community structure in PM10 and PM2.5 had significant seasonal difference?P<0.05?.The diversity of bacterial community in winter and summer was higher than that in autumn.The composition of the bacterial community in the different seasons was small at the level of the phylum,and there were significant differences in the genus level.The dominant genus were different in each season.?7?The abundance and diversity of bacterial communities structure in PM100 and PM2.5 at different sampling points show no significant difference?P>0.05?,and at the level of the phylum and genus,the difference in bacterial community structure at different sampling points was small and the similarity was high.?8?Redundancy analysis was used to study the correlation between environmental factors and bacterial community structure in different seasons.Temperature and PM10 were the main factors affecting the bacterial community structure in summer.Humidity and PM10 were the main factors affecting the distribution of bacterial community in autumn,and CO,NO2 and PM2.5 are the main factors affecting the bacterial community in winter. |
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