Atmospheric transport is critical to dispersal of microorganisms between habitats, and this underpins resilience in terrestrial and marine ecosystems globally. A key unresolved question is whether microorganisms assemble to form a taxonomically distinct, geographically variable, and functionally adapted atmospheric microbiota. This question is made more complex by the unique challenges of separating potential contaminants from atmospheric signal, particularly given the ultra-low biomass of air and the long durations of sampling where contamination may occur. Here we adopted a comprehensive data filtering approach to mitigate contamination and characterise inter-continental patterns of microbial taxonomic and functional diversity in air within and above the atmospheric boundary layer and in underlying soils for 596 globally sourced samples. Bacterial and fungal assemblages in air were taxonomically structured and deviated significantly from purely stochastic assembly. Patterns differed with location and reflected climate, underlying surface cover and environmental filtering. Source-tracking indicated a complex recruitment process involving local soils plus globally distributed inputs from drylands and the phyllosphere. Assemblages displayed stress-response and metabolic traits relevant to survival in air, and taxonomic and functional diversity were correlated with macroclimate and atmospheric variables. Our findings highlight complexity in the atmospheric microbiota that is key to understanding regional and global ecosystem connectivity.
Non-erodible elements such as stones and vegetation are key to controlling wind erosion and dust emission in drylands. Stony deserts are widely distributed in the Gobi Desert, but the effect of stones on wind erosion and dust emission have not been well studied, except under artificial conditions. In this study, we evaluated the effect of stones on wind erosion and dust emission by measuring the sand saltation threshold in a stony desert in Tsogt-Ovoo in the Gobi Desert, Mongolia, under natural surface conditions during sand and dust storms. We quantified the amount of stones by measuring the roughness density, and determined the threshold friction velocity for sand saltation by measuring wind speed and sand saltation count. Our results showed that the threshold friction velocity increased with the roughness density of stones. In the northern part of the study area, where neither a surface crust nor vegetation was observed, the roughness density of stones was 0.000 in a topographic depression (TD), 0.050 on a northern slope (N.SL), and 0.160 on the northern mountain (N.MT). The mean threshold friction velocity values were 0.23, 0.41, and 0.57 m/s at the TD, N.SL, and N.MT sites, respectively. In the southern part of the study area, the roughness density values of stones were 0.000 and 0.070-0.320 at the TD and southern slope sites, respectively, and the mean threshold friction velocities were 0.23 and 0.45-0.71 m/s, respectively. We further compared the observed threshold friction velocities with simulated threshold friction velocities using Raupach's theoretical roughness correction and the measured roughness density values, and found that Raupach's roughness correction worked very well in the simulation of threshold friction velocity in the stony desert. This means that the results of our stone measurement can be applied to a numerical dust model.
In this paper, we attempted to determine the most stable or unstable regions of vegetation cover in Mongolia and their spatio-temporal dynamics using Terra/MODIS Normalized Difference Vegetation Index (NDVI) dataset, which had a 250-m spatial resolution and comprised 6 periods of 16-day composited temporal resolution data (from 10 June to 13 September) for summer seasons from 2000 to 2012. We also used precipitation data as well as biomass data from 12 meteorological stations located in 4 largest natural zones of Mongolia. Our study showed that taiga and forest steppe zones had relatively stable vegetation cover because of forest characteristics and relatively high precipitation. The highest coefficient of variation (CV) of vegetation cover occurred frequently in the steppe and desert steppe zones, mainly depending on variation of precipitation. Our results showed that spatial and temporal variability in vegetation cover (NDVI or plant biomass) of Mongolia was highly dependent on the amount, distribution and CV of precipitation. This suggests that the lowest inter-annual CV of NDVI can occur during wet periods of growing season or in high precipitation regions, while the highest inter-annual CV of NDVI can occur during dry periods and in low precipitation regions. Although the desert zone received less precipitation than other natural zones of the country, it had relatively low variation compared to the steppe and desert steppe, which could be attributed to the very sparse vegetation in the desert.
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