Effects Of Atmospheric Particulates On Physiology And Microbial Community Structure On Leaf Surface Of Haplocladium Microphyllum And Hypnum Plumaeforme

With the increasing degree of human disturbance to the environment,using biology to instruct and monitor environmental pollution has become one of the current trends in environmental biology.As a good indicator of environmental pollution,bryophytes have been widely used to monitor various environmental changes in the world.Atmospheric particulates are common pollutants in the atmosphere,which are the direct cause of fog and haze.They not only reduce visibility,but also cause deep-seated problems such as health,environment and ecology.However,most of studies focus on their health and environmental effects,ignoring ecological effects.The physiological and biochemical changes in bryophytes and the changes of microbial community structure on leaf surface directly in contact with atmospheric particulates have been rarely studied and reported.Atmospheric particulates were collected from constructed wetlands and urban streets.Haplocladium microphyllum and Hypnum plumaeforme were selected as research objects.The effects of atmospheric particulates from different sources on physiological and biochemical indices of bryophytes and bacterial community structure on leaf surface were analyzed.The experimental results showed that:?1?The atmospheric particulates from urban streets and constructed wetlands had significant effects on the physiological and biochemical indexes of bryophytes.With the increase of particulate concentration,the contents of total chlorophyll decreased gradually,while the contents of soluble sugar,soluble protein,free proline and peroxidase activity increased continuously.Physiological and biochemical indices of bryophytes sprayed with particulates from urban streets changed more than those sprayed with constructed wetlands.?2?Under the same stress environment,the changes of total chlorophyll,soluble sugar,soluble protein,free proline content and peroxidase activity of Hypnum plumaeforme were greater than those of Haplocladium microphyllum.?3?The analysis of bacterial community diversity on the leaf surface of Haplocladium microphyllum and Hypnum plumaeforme showed that the richness indexes of bryophytes sprayed with urban streets particulates were the highest,followed by that sprayed with constructed wetlands particulates,and bryophyte sprayed with sterile mineral water were the lowest.?4?The results showed that spraying particulates could increase the bacterial diversity on the leaf surface of bryophytes,and the number of bacterias sprayed with urban streets were more than that in sprayed with constructed wetlands.Before spraying,there were 24 phylums and 60 classes of bacteria in Haplocladium microphyllum,after spraying particulates from constructed wetlands and urban streets,the number of phylums increased to 26,the classes increased to 64 and the number of phylums increased to 29,the classes increased to 69;Before spraying,there were 22phylums and 56 classes of bacteria in Hypnum plumaeforme,after spraying the particulate from constructed wetlands and urban streets,the number of phylums increased to 24,the classes increased to 59 and the number of phylums increased to24,the classes increased to 63.?5?The relative abundance of each phylum and class of bacteria changed in the bacterial community sprayed with different sources of particulates,but the dominant phylum and class of bacteria did not change.The dominant phylums of Haplocladium microphyllum include Proteobacteria,Bacteroidetes,Cyanobacteria,Verrucomicrobia,Acidobacteria,Gemmatimonadetes,Firmicutes,Chloroflexi and Actinobacterias.The dominant phylums of Hypnum plumaeforme include Proteobacteria,Bacteroidetes,Cyanobacteria,Verrucomicrobia,Acidobacteria,Chloroflexi and Actinobacterias.?6?Bacteria associated with the degradation of certain pollutants were found on the surface of bryophytes leaves sprayed with particulates.For example,Limnobacter thiooxidans in Haplocladium microphyllum could reduce Cr⁶⁺,Phenylobacterium koreense could degrade petroleum,and Thioalkalivibrio nitratireducens could reduce nitrite to ammonia.Cidibacter ferrireducens in Hypnum plumaeforme is a new type of acidophilic iron-reducing bacteria,Methylophaga nitratireducenticrescens is a denitrifying bacteria,Sandaracinus amylolyticus and Nostoc punctiform could fix nitrogen,Thioalkalivibrio nitratireducens could reduce nitrite and hydroxylamine to ammonia.?7?Some bacteria adapted to the changes of physiological and biochemical indices were found on the surface of bryophytes leaves sprayed with particulates.Chryseolinea Serpens in Haplocladium microphyllum and Hypnum plumaeforme could degrade the rising sugars caused by particulates stress.Thermoactinomyces vulgaris,Nitrosospira multiformis and Fluviicola hefeinensis of Hypnum plumaeforme respectively could hydrolyze carbohydrates,control the movement of various proteins in cels,produce catalase to decompose hydrogen peroxide.It is concluded that the changes of bacterial community structure on bryophytes leaf surface caused by atmospheric particulats are partly due to the direct changes of external environment,and partly due to the influence of external environment on the physiological and biochemical characteristics of bryophytes,thus indirectly changing the bacterial community structure on the leaf surface.