Characterization Of Atmospheric Bioaerosols Along The Transport Pathway Of Asian Dust In Northern China

Previous studies have shown that bioaerosols are injected into the atmosphere during dust events.These bioaerosols may affect leeward ecosystems,human health and agricultural productivity and may even induce climate change.However,bioaerosol dynamics have rarely been investigated along the transport pathway of Asian dust,especially in China,where dust events affect huge areas and massive numbers of people.In view of this,this paper mainly focuses on the bioaerosols along the dust transport pathway in northern China.Joint field sampling experiment was carried out at three places which were along the highway from Dalanzadegade to Ulanbator,Erenhot of Inner Mongolia and Zhangbei of Hebei Province respectively.The morphology and concentrations of bioaerosols were analyzed by fluorescence microscopy,and atmospheric microbial community structures were analyzed by high-throughput sequencing technology.The amount and community structure of bioaerosols during the dust events were obtained,which provided basic data for further study of the climatic effects of bioaerosols.The main results are as follows:?1?There are a lot of microorganisms in the dust.The concentrations of bacteria in non-dust samples ranged from 10⁴ to 10⁵ m^-3,while that in dust samples ranged from 10⁵ to 10⁶ m^-3.During the dust period,the concentration of bacteria increased by one or two orders of magnitude,and the concentration of organic matter increased by two or three orders of magnitude.The dust contained a large number of microbial aggregates,in which microorganisms might metabolize or even reproduce,so the concentration of atmospheric bioaerosols might be underestimated.?2?During the dust events,the increase of bacterial concentration is not only due to the increase of dust particles,but also due to the large number of exogenous microorganisms carried in long-distance transport dust.The concentration ratios of bacterial particles to organic particles increased from 5.1%+6.3%in non-dust samples to 9.8%+6.3%in dust samples,which indicate that one unit organic matter in dust samples could contain more bacteria than that in non-dust samples.?3?The dust carries a rich variety of bacteria.As for Erenhot,the number of OTUs?operational taxonomic unit?,Shannon index and Simpson index of bacterial community in dust samples were higher than those in non-dust samples,while the alpha diversity of fungi in dust samples was not different significantly from that in non-dust samples.The high throughput sequencing results showed that prokaryotes in the samples were abundant,including 34 phyla,94 classes,166 orders and 243families.Besides,there were 3 phyla,19 classes,62 orders and 149 families of fungi in the samples.The ubiquitous bacterial phyla in the samples were Acidobacteria,Actinobacteria,Bacteroidetes,Chloroflexi,Firmicutes,Gemmatimonadetes,and Proteobacteria.Of these phyla,Actinobacteria,Bacteroidetes,and Proteobacteria remained the dominant phyla in all the samples.Some archaea,such as Crenarchaeota and Euryarchaeota were detected,but their relative abundances were much lower compared to the dominant bacterial phyla.The main fungi in the samples are Ascomycota and Basidiomycota,and there was also a much lower relative abundance of Chytridiomycota.At the class level,Agaricomycetes,Dothideomycetes,and Sordariomycetes were predominant,and the dust samples contained more diverse fungal classes compared with non-dust samples.?4?There are obvious differences of bacterial community structure in dust and non-dust samples,and dust events will significantly change the microbial community of local atmosphere.At the phylum level,as for Erenhot,the relative abundances of Acidobacteria and Chloroflexi in dust samples had a remarkable rise compared with non-dust samples,followed by Crenarchaeota,Firmicutes,and Proteobacteria.The relative abundance of Proteobacteria in all dust samples increased slightly compared with that in non-dust samples,and Alpha-proteobacteria made the major contribution among this group;by contrast,Gamma-proteobacteria was just the reverse.The dust samples of Erenhot have some homology with those of outer Mongolia.