<p>The prevalence of pollen allergy is increasing worldwide, as is the proportion of people living in cities. Thus, there is an increasing importance to investigate pollen distribution across city districts. We conducted two sampling campaigns to investigate the spatial and temporal variation of airborne pollen in the Sydney metropolitan area and the vertical variation within a forest in north-western Sydney.</p><p>Spatial assessment of pollen deposition was made for eight weeks in the exceptionally dry summer in 2019/2020 using gravimetric samplers. These samplers were set up at ten locations characterised by different degrees of urbanisation and distance to the sea. We focussed on the most abundant pollen types and investigated statistical relationships with land use and meteorology. In addition, we compared our results with pollen data of previous years sampled at a pollen monitoring station located in north-western Sydney in a semi-rural environment. We measured vertical pollen concentrations in a native forest, which mostly consists of Eucalypt trees (family Myrtaceae) in north-western Sydney. A scaffolding was equipped with five portable volumetric pollen samplers installed at different heights (1, 4, 10, 16, 20.5 m above ground level (agl)). We measured pollen concentration every second hour between 9 am and 4 pm on a total of four days in January 2020. We compared concentrations between days, heights, and times of the day.</p><p>The most abundant pollen type registered within our sampling campaigns belonged to the family Myrtaceae. Grass pollen (Poaceae) was also detected, but in much smaller quantities which can be attributed to the drought and temporal setting of the campaign, which started in the post-peak period of a comparably weak pollen season associated with a smaller number of days with medical relevance (> 50 pollen grains/m<sup>3</sup>). Our data showed spatial variations between the ten locations, but no relationship with land use (grass and tree cover) and meteorology could be found. This suggests the influence of other factors such as long-range pollen transport or resuspension of pollen. In the forest, Myrtaceae concentrations varied between days, sampling height and time of the day: the highest concentration was recorded on the second day of measurement between 9 and 10 am at 10 m agl. Peak values were generally reached between 1 and 2 pm. Considering sampling height, concentrations were on average highest at 4 m agl. The location of pollen sources as well as meteorological conditions such as turbulence and variation in wind speed may be key determinants of small-scale differences of pollen concentrations.</p><p>The drought preceding this study did not only influence the length but also the strength of the pollen season. Data on vertical variations could support investigations related to turbulence, which is also responsible for resuspension processes.</p>
Abstract There is a need for information on pollen exposure to assess allergy risk. Monitoring of aeroallergens in a city is usually limited to the use of a single trap for the whole area. While a single trap provides enough information on background pollen concentration for the area, varying pollen exposure across different urban environments, however, is not considered. In this study, we analysed aerobiological data of three pollen seasons (2017–2020) recorded with a volumetric pollen trap in Sydney, Australia. In order to assess spatial differences in pollen exposure across the city, we installed ten gravimetric traps recording pollen deposition for eight weeks during the summer of 2019/2020. We considered the influence of meteorological variables, land use, urbanisation and distance to the sea. Our results showed differences in pollen season characteristics across the three analysed seasons and correlations with meteorological parameters. Considering all years, we found for Poaceae and Alternaria the strongest positive correlation with mean temperature and for Myrtaceae and Cupressaceae with maximum temperature. Likewise, there were negative correlations with humidity (Myrtaceae, Cupressaceae, Alternaria ) and precipitation (Myrtaceae, Cupressaceae). Days with medically relevant pollen and spore concentrations varied between years and we recorded the highest amount in 2017/2018 for Poaceae and Alternaria and in 2019/2020 for Myrtaceae. In addition, we found spatial and temporal variations of pollen deposition. However, we did not detect significant correlations between pollen deposition and land use, which can be attributable to drought conditions prior to the sampling campaign and the temporal setting in the pollen season. This study highlights the importance of continuous volumetric aerobiological monitoring as well as the assessment of pollen exposure at several locations across a large urban area.
Grasses populate most biogeographical zones, and their diversity influences allergic sensitisation to pollen. Previously, the contribution of different Poaceae subfamilies to airborne pollen has mostly been inferred from historical herbarium records. We recently applied environmental (e)DNA metabarcoding at one subtropical site revealing that successive airborne grass pollen peaks were derived from repeated flowering of Chloridoid and Panicoid grasses over a season. This study aimed to compare spatiotemporal patterns in grass pollen exposure across seasons and climate zones. Airborne pollen concentrations across two austral pollen seasons spanning 2017–2019 at subtropical (Mutdapilly and Rocklea, Queensland) and temperate (Macquarie Park and Richmond, New South Wales) sites, were determined with a routine volumetric impaction sampler and counting by light microscopy. Poaceae rbcL metabarcode sequences amplified from daily pollen samples collected once per week were assigned to subfamily and genus using a ribosomal classifier and compared with Atlas of Living Australia sighting records. eDNA analysis revealed distinct dominance patterns of grass pollen at various sites: Panicoid grasses prevailed in both subtropical Mutdapilly and temperate Macquarie Park, whilst Chloridoid grasses dominated the subtropical Rocklea site. Overall, subtropical sites showed significantly higher proportion of pollen from Chloridoid grasses than temperate sites, whereas the temperate sites showed a significantly higher proportion of pollen from Pooideae grasses than subtropical sites. Timing of airborne Pooid (spring), Panicoid and Chloridoid (late spring to autumn), and Arundinoid (autumn) pollen were significantly related to number of days from mid-winter. Proportions of eDNA for subfamilies correlated with distributions grass sighting records between climate zones. eDNA analysis enabled finer taxonomic discernment of Poaceae pollen records across seasons and climate zones with implications for understanding adaptation of grasslands to climate change, and the complexity of pollen exposure for patients with allergic respiratory diseases.
Background Grasses populate most biogeographical zones, and their diversity influences allergic sensitisation to pollen for allergy patients. Previously, the contribution to airborne pollen of different Poaceae subfamilies has mostly been inferred from historical herbarium records. We recently applied environmental (e)DNA metabarcoding at one subtropical site revealing that successive airborne grass pollen peaks were derived from repeated flowering of Chloridoid and Panicoid grasses over a season. This study aimed to compare spatiotemporal patterns in grass pollen exposure between biogeographical zones.MethodsAirborne pollen concentrations over two austral pollen seasons spanning 2017-2019 at subtropical (Mutdapilly and Rocklea, Queensland) and temperate (Macquarie Park and Richmond, New South Wales) sites, were determined with a routine volumetric impaction sampler and counting by light microscopy. Poaceae rbcL metabarcode sequences amplified from daily pollen samples collected once per week were assigned to subfamily and genus using a ribosomal classifier and compared with Atlas of Living Australia sighting records.ResultsPollen eDNA reads of Panicoid grasses were most common in the subtropical Mutdapilly site (89.3% of Poaceae reads) and the temperate Macquarie Park site (61.3%), whilst Chloridoid grasses dominated the subtropical Rocklea site (68.7%). Overall, subtropical sites showed significantly higher proportion of pollen from Chloridoid (38.5%) grasses than temperate sites (19.5%, p=0.0045), whereas the temperate sites showed a significantly higher proportion of operational taxonomic units for Pooideae (12.6%) grasses than subtropical sites (2.1%, p=0.0101). Timing of airborne Pooid (spring), Panicoid, Chloridoid, and Arundinoid (autumn) pollen were significantly related to days since mid-winter. Proportions of eDNA for grass subfamilies correlated with spatial distributions grass subfamily sighting records (R2=0.815, p=0.0021).ConclusionsThe capacity of eDNA metabarcoding for finer taxonomic discernment of Poaceae subfamilies in local airborne pollen records has implications for understanding adaptation of grasslands to climate change and the complexity of pollen exposure for patients with allergic respiratory diseases.
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