Chemical Composition and Bacterial Community in Size-Resolved Cloud Water at the Summit of Mt. Tai, China

A three-stage collector was used to collect size-resolved cloud samples at the summit of Mt. Tai. Subsequently, analyses of pH values, water-soluble ions, and trace metals were performed and bacterial community were conducted using MiSeq amplicon sequencing. The pH values of the samples decreased as droplet sizes decreased. Sulfate (SO42-), nitrate (NO3-) and ammonium (NH4+) were the main secondary inorganic ions which their concentration distributed significantly different from size-resolved cloud water. The NH4+ concentration was higher in smaller droplets. The SO42- and NO3 concentrations were higher in larger droplets. The Ca2+ concentration increased as droplet size increased. Small droplet samples tended to have lower pH value, mainly because of the more acidic (SO42- and NO3-) and less acid-neutralizing (NH4+ and Ca2+) components. The bacterial community in size-resolved cloud samples were firstly recognized and dominated by the genera of Lactococcus (average abundance 34.9%) and Bacillus (average abundance 34.0%). Linear discriminant analysis effect size (LEfSe) revealed differences of the bacterial community in size-resolved cloud water samples, which was probably caused by the bacterial size. Redundancy analysis suggested several minor correlations that the H2O2, NO2- concentrations, and trace metals exert effects on the bacterial community.