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The ongoing fragmentation of ash populations due to ash dieback requires an effective gene flow between individuals; thus, investigations on ash pollen transport are essential. In this study, comprehensive aerobiological field experiments at two seed plantations in Baden-Württemberg were conducted in 2019 and 2020 in order to study the influence of...
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Early peaks of airborne ragweed (Ambrosia L.) pollen concentrations were observed at several monitoring stations in Hungary in June 2017 and 2018, one month before the usual start of the pollen season at the end of July. Backward trajectories were calculated to simulate potential sources of pollen collected at different locations in the Pannonian B...
Citations
... The question of the transport of Fraxinus pollen grains is still widely debated. Some studies (Bacles and Ennos, 2008, Bacles et al., 2005, Eisen et al., 2023, FRAXIGEN, 2005, Thomasset et al., 2014 report that they could indeed disperse over long distances, resulting in high gene flow via pollen movement, while others (Eisen et al., 2022, Heuertz et al., 2003, Semizer-Cuming et al., 2021 report moderate pollen flow over long distances. For this reason, we consider the identification of wood charcoal remains to be a more reliable marker for the presence of Fraxinus in Cyprus. ...
... Vol.: (0123456789) or again, those located on the banks of the Tormes River, can reach the particle collector, since the transport of ash pollen is usually between 70-1900 m (Bacles & Ennos, 2008;Eisen et al., 2022;Heuertz et al., 2003;Semizer-Cuming et al., 2021). In contrast, other authors who have carried out aeropalynological studies in the city of Salamanca differ in their results for this pollen type, obtaining negative correlations for the north-easterly and north-westerly quadrant and positive ones for the north-westerly (Fuentes Antón, 2020) or positive ones for the north-westerly and north-westerly quadrant (Rodríguez de la Cruz, 2009). ...
The allergenic nature of ash (Fraxinus sp.), an important element of the dehesas, has been poorly studied in meridional Europe owing to the low concentrations of this pollen type in the atmosphere. However, it has cross-reactivity with Olea L. and other homologous allergens of trees and herbaceous species, leading to earlier and more prolonged respiratory allergenic symptoms. The main aims of this work were to characterize the main pollen season (MPS) of ash from 2011 to 2022, to evaluate the influence of meteorological variables on airborne concentrations of this pollen type and to elaborate a pollen calendar for Fraxinus in Salamanca. The aeropalynological analysis for the eleven years of the study shows that the MPS for Fraxinus begins on 27 th December until 4 th April with an average duration of 100 days, a mean peak value of 57 grains/m³ reached on 22 nd February and a mean annual pollen integral of 567 grains/m³, observing an earlier onset of MPS, an increase in its duration and a decrease in its concentrations, presumably linked to climate change. Regarding the influence of meteorological parameters on pollen concentrations, positive correlations were found for maximum and mean temperatures and insolation, as well as southeast winds and frequency of calms, while negative correlations were reported for precipitation, relative humidity, and wind speed. The analyze of Fraxinus pollen could be used to predict seasonal behavior and warn people who may suffer pollinosis either from ash pollen or from cross-reactivity events.
... Passive spore traps were prepared and implemented as previously described (Aguayo et al. 2018;Eisen et al. 2022) with paper filters (Whatman® No1, 15 cm in diameter) and Vaseline® and incubated for 7 days at a height of 160 cm (Fig. 1C). Two spore traps were incubated for a duration of seven days at the Kaisheim site (Plot 1, Fig. 3D), with incubation starting on 22 June 2022 and 29 June 2022. ...
The ascomycete Hymenoscyphus fraxineus causes the devastating ash dieback disease of European ash ( Fraxinus excelsior L.). Spore traps are often used to measure the amount of ascospores in the environment, but the pathogen-load of the soil in ash stands has not been recorded so far. This is of particular interest with regard to the occurrence of ash stem necrosis, a decisive factor for the severe course of the disease. In order to gain a more differentiated insight into the pathogen-load in ash stands, we analysed soil samples from four ash tree sites in southern Germany, covering a clone plantation, two seed orchards and a forest. The pathogen-load was determined using a quantitative TaqMan real-time PCR assay for ten to twenty plots per stand. Results obtained by the species-specific assay highlighted that the pathogen-load is heterogeneously distributed in the ash stands. H. fraxineus DNA targets were detected in 17% of the soil samples. The pathogen-load differed according to soil depth, with the highest pathogen abundance in the top 5 cm, followed by 5–10 cm and finally 10–15 cm. Pathogen-load and thereby infection pressure were found to be highly variable for the individual trees in one stand. Overall, the study discovered detectable levels of H. fraxineus in the soil of all four study sites, which supports the hypothesis that H. fraxineus can be found in the soil of ash stands. The qPCR approach was found to be an effective method for monitoring the load of H. fraxineus in soil and for demonstrating the successful application of the method on the sample type of custom-made spore traps. Results suggest the implication of site-specific pathogen-load determination in future H. fraxineus -monitoring and selection of less susceptible ash trees for breeding and seed production.
... In 2023, from initially 416 individuals, only 120 living ash trees remained on the plantation. Both ash seed plantations have already been the subject of ash dieback research in other studies (Enderle et al. 2015;Buchner et al. 2022;Eisen et al. 2022Eisen et al. , 2023Eisen et al. , 2024. ...
Key message
Ash dieback causes alterations in leaf physiology and morphology, particularly affecting the specific leaf area, which can be used to discriminate between different degrees of damage.
Abstract
Since the introduction of the invasive fungal pathogen Hymenoscyphus fraxineus in Europe, the European common ash (Fraxinus excelsior L.) has been threatened by ash dieback. An infection leads, for example, to typical symptoms of dying shoots, but changes of leaf physiology and morphology are still largely unexplored. Therefore, five physiological and morphological traits, chlorophyll content, chlorophyll fluorescence, specific leaf area, leaf thickness, and fluctuating asymmetry, were investigated in four different study sites in southern Germany regarding possible changes due to ash dieback and their relationship to different degrees of damage. Both higher and lower levels of chlorophyll with increasing damage due to ash dieback were observed. Chlorophyll fluorescence and fluctuating asymmetry proved to be less suitable indicators of damage. Leaf thickness showed the tendency (however not significant) of an increase in more severely damaged trees. The specific leaf area was identified as a suitable indicator of the damage severity, with significant smaller values in less healthy trees. Therefore, ash dieback can also result in notable alterations in leaf physiology and morphology.
... Thus, disease development at the stand level is dependent on less susceptible genotype ability to spread their genes via pollen and seed (Lobo et al. 2015;Semizer-Cuming et al. 2019. Due to the large-scale decline of the populations, it is also necessary that the ash trees are sufficiently linked with each other and produce viable pollen, which can be transported over long distances (Buchner et al. 2022;Eisen et al. 2022). ...
... Mature seeds drop in late autumn and remain dormant for two to six winters before germinating (Douglas et al. 2013;Bajc et al. 2020). Since pollen and seeds are both dispersed by wind, fragmented ash populations result in limited gene flow and pollination success (Fussi et al. 2014;Eisen et al. 2022). Heuertz et al. (2003) determined a mean seed dispersal distance of 14 m in a mixed deciduous forest in Romania, and Morand et al. (2002) suggested 140 m in continuous forests across France. ...
Forest tree species reproduction is a key factor in maintaining the genetic diversity of future generations and the stability of forest ecosystems. The ongoing ash dieback disease could affect the reproductive ecology of Fraxinus excelsior L. and have a major impact on the quantity and quality of pollen and seeds. In this study, we investigated pollen production and viability of pollen and seeds of ash trees with different health status from 2018 to 2022. Inflo-rescences were collected from 105 trees (pollen production), pollen from 125 trees (pollen viability), and seeds from 53 trees (seed quality) in two seed orchards and in one flood-plain forest in southern Germany. Not all parameters were examined at every site every year. The average pollen production per tree was estimated at 471.2 ± 647.9 billion pollen grains. In addition, we found that a high number of inflores-cences did not equate to high pollen production per inflores-cence. Pollen production of healthy and diseased trees did not differ significantly, although only 47% of severely diseased male trees (vs. 72% for healthy trees) produced flowers. With regards to pollen viability, the TTC test showed an average viability of 73% ± 17%. Overall, there was a slight tendency for diseased trees to have less viable pollen. However, a significant difference could only be calculated for trees in the floodplain forest. The percentage of germi-nable seeds in 2018 was 38% in the floodplain forest and 57% in one of the seed orchards. The percentage of viable seeds (TTC test) ranged from 17 to 22% in the orchards in 2020. Non-viable seeds were usually heavily infested by insects. In general, seed quality was not significantly different between healthy and diseased trees. Our results indicate that ash dieback affects flower formation and pollen viability but not pollen production or seed quality. Nevertheless, the fact that hardly any flowering was observed, especially for trees that were seriously affected, suggests a negative effect of ash dieback on reproductive performance. Thus, severely diseased trees will transfer their genes to a smaller extent to the next generation.
... Pollen also triggers potentially deadly thunderstorm asthma (Idrose et al., 2020;Nickovic et al., 2023). Hence, understanding pollen dispersion dynamics is important to reduce the societal risks posed by allergens (Eisen et al., 2022;Hernandez-Ceballos et al., 2014). ...
An area with the potential of producing high concentrations of airborne pollen is defined as the ‘potential pollinosis area’. However, the detailed dynamics of pollen dispersion are not fully understood. Further, studies on the detailed dynamics of the pollen-generating environment are limited. This study aimed to determine the relationship between the dynamics of potential pollinosis areas and annual meteorological factors with high spatiotemporal resolution. We visualised and analysed the dynamics of the potential polliosis area based on 11–year high-spatial-density observation data for the atmospheric concentrations of Cryptomeria japonica pollen. The results showed that the potential pollinosis area headed northeast with repeated expansion and contraction, while the centre of the potential pollinosis area leaped to the north in mid-March. The deviation in the fluctuation of the coordinates for the potential pollinosis area before the northward leap was strongly related to the deviation in the relative humidity of the previous year. These results indicated that the pollen grains of C. japonica across Japan are distributed based on the meteorological conditions of the previous year until mid-March, after which, the pollen grains are distributed through flowering synchrony. Our results suggest that daily nationwide flowering synchrony has a significant annual impact, and changes in relative humidity caused by, for example, global warming would affect the occurrence and predictability of seasonal changes in the pollen dispersion dynamics of C. japonica and other pollen-producing species. Our study showed that pollen production by C. japonica through flowering synchrony is a major cause of nationwide pollinosis and other allergy-related health problems.
... In this study, self-constructed gravimetric pollen traps [30,31] based on the principles published by Durham [32] were used to determine pollen deposition ( Figure 4). These traps passively collect airborne pollen by gravimetric deposition on a horizontally orientated microscope slide, which was coated with Vaseline. ...
... The gravimetric traps we used were a cost-effective way to cover pollen sampling at several locations and were successfully used in recent studies [30,31,[39][40][41]. However, limitations of the method need to be considered when discussing and interpreting results. ...
There is only little and partially contradicting knowledge on the variation of pollen abundance at different altitudes in mountainous regions. The aim of this work is to gain new insights on the influence of wind and surrounding trees on the deposition and transport of birch (Betula spec.) pollen in the Bavarian Alps, Germany. Data on birch pollen deposition were collected at five sites using gravimetric traps along an altitudinal gradient from Garmisch-Partenkirchen (720 m a.s.l.) to the Environmental Research Station Schneefernerhaus (2650 m a.s.l) in the pollen season 2020. We compared these data with birch pollen concentration derived from a volumetric trap at Schneefernerhaus and with phenological data, i.e., flowering onset times observed at 21 birch trees at different altitudes. Wind data were gathered directly at or near each pollen trap and surrounding birch trees were mapped in the field. Whereas the pollen load was lowest at the highest location, substantially higher values were measured at medium altitudes (1300–1600 m a.s.l.). This can be explained by the pronounced mountain-valley wind system, which ensured the transport of pollen to the corresponding altitudes. We conclude that pollen levels are influenced by topography, local wind systems and the availability of pollen. Pollen levels in complex mountainous environments are therefore not substantially affected by the occurrence of birch trees in the immediate vicinity.
Key message: Paternity analyses show that effective pollination of ash (Fraxinus excelsior L.) in a seed orchard and a floodplain forest affected by ash dieback is more likely to be facilitated by healthier males. Thereby, natural selection can have a positive effect on the health of future generations.
Context: Ongoing ash dieback and increasing fragmentation of ash populations may result in reduced pollen flow, which can reduce pollination success of future generations of ash trees. Therefore, it is essential to further improve our understanding of gene flow patterns, especially with respect to ash dieback.
Aims: In this study, paternity analyses were conducted in a seed orchard and a floodplain forest in Germany in 2018 to explain the relationship between pollination success and the health status of ash trees and distances of effective pollen transport.
Methods: Cambium samples (i.e., from twigs and stumps) were collected from 251 ash trees (putative father and mother trees) for genotyping, and the health status of each tree was documented using a scoring system to evaluate vitality. Additionally, seeds were harvested from 12 mother trees per site. Genetic analyses using nuclear microsatellites were performed to determine paternal trees. Paternities were assigned based on the likelihood model implemented in the Cervus 3.0.7 software.
Results: Our results showed that the average pollination distance was 76 m in the seed orchard and 166 m in the floodplain forest. In general, pollination success decreased substantially with increasing distance to the mother tree. Despite the dense tree cover in the floodplain forest, pollen were transported over long distances (greater than 550 m), suggesting that non‑local sources also play a role in pollination. This is supported by the foreign pollen input identified in the seed orchard (66.5%). Self‑pollination was detected only to a very small extent, and thus had no major influence on reproduction. In addition, both healthy and slightly diseased father trees showed similar mating success. However, this was not the case for the severely diseased ash trees (more than 50% of crown damage)
because only a few offspring could be assigned to them. Nevertheless, in contrast to the floodplain forest, there was no significant correlation between damage classes and pollination success in the seed orchard.
Conclusion: Long‑distance pollen transport contributes to the connectivity of ash trees in the landscape. Additionally, both healthy and slightly diseased fathers have a greater contribution to pollination, thus potentially improving the health of the next generation of ash trees. Moreover, gene flow between stepping stone populations is necessary to ensure the positive impact on the genetic diversity of ash populations in the future.
