Heat and chill requirements of Fraxinus flowering in Galicia (NW Spain)

Fraxinus pollen data from eight Galician localities (1999-2003), recorded using 7-day Lanzoni VPPS pollen traps, were studied to determine their temporal and spatial distribution. The determination of the chill and heat required to trigger flowering and the start cumulative date were calculated using ten years of pollen data from Ourense. The sum of maximum temperatures from the 55 days before the peak date showed the lowest standard deviation coefficient and the mean quantity of accumulated heat was 741. Temperatures below 0°C and/or rainfall at the beginning of flowering caused a longer period before the peak date was registered. Temperatures recorded in November were very important for chill accumulation and determine the heat requirement needed to trigger Fraxinus flowering in Galicia.     

Defining the twig fungal communities of Fraxinus species and Fraxinus excelsior genotypes with differences in susceptibility to ash dieback

Ash dieback disease (caused by Hymenoscyphus fraxineus) has affected European ash species (Fraxinus spp.) in recent decades. However, some Asian and American species of Fraxinus and certain genotypes of Fraxinus excelsior are less affected by the disease. We used ITS1-metabacoding to explore the drivers influencing diversity and composition of the twig fungal communities of Fraxinus species and F. excelsior genotypes. Our results revealed that fungi in the classes Eurotiomycetes and Dothideomycetes were among the most prevalent taxa in both Fraxinus species and F. excelsior genotypes. The diversity of the fungal communities differed significantly among Fraxinus species and could be explained by seed origin. Neither host genotype nor season had a significant effect on the community diversity of F. excelsior genotypes. On the other hand, the composition of twig fungal communities differed significantly among host species and among F. excelsior genotypes, and in F. excelsior there was also a significant effect of season on the composition of the fungal community. We did not find a clear effect of ash dieback susceptibility on either diversity or composition of fungal communities in twigs of Fraxinus species, although the effect was significant on the composition of fungal communities among F. excelsior genotypes. Our results demonstrated differences in fungal communities among species of Fraxinus and of F. excelsior genotypes, suggesting specific relationship between individual host genotypes and endophytic fungi.     

Thank you for not flowering: conservation genetics and gene flow analysis of native and non-native populations of Fraxinus (Oleaceae) in Ireland

The risks of gene flow between interfertile native and introduced plant populations are greatest when there is no spatial isolation of pollen clouds and phenological patterns overlap completely. Moreover, invasion probabilities are further increased if introduced populations are capable of producing seeds by selfing. Here we investigated the mating system and patterns of pollen-mediated gene flow among populations of native ash (Fraxinus excelsior) and mixed plantations of non-native ash (F. angustifolia and F. excelsior) as well as hybrid ash (F. excelsior × F. angustifolia) in Ireland. We analysed the flowering phenology of the mother trees and genotyped with six microsatellite loci in progeny arrays from 132 native and plantation trees (1493 seeds) and 444 potential parents. Paternity analyses suggested that plantation and native trees were pollinated by both native and introduced trees. No signs of significant selfing in the introduced trees were observed and no evidence of higher male reproductive success was found for introduced trees compared with native ones either. A small but significant genetic structure was found (φ_ft=0.05) and did not correspond to an isolation-by-distance pattern. However, we observed a significant temporal genetic structure related to the different phenological groups, especially with early and late flowering native trees; each phenological group was pollinated with distinctive pollen sources. Implications of these results are discussed in relation to the conservation and invasiveness of ash and the spread of resistance genes against pathogens such as the fungus Chalara fraxinea that is destroying common ash forests in Europe.     

Transport of Photoassimilates in Young Trees of Fraxinus and Sorbus: Measurement of Translocation in vivo

Abstract: Translocation of photoassimilates was studied on 2-year-old trees of Fraxinus excelsior and Sorbus aucuparia using the short-lived isotope ¹¹C. Leaflets of different leaves on the same plants were radiolabeled showing that both carbon distribution and speeds of transport may vary with leaf position. Within 2 h after pulse feeding with ¹¹CO₂, mainly the lower leaves distributed radiolabel to the roots in Fraxinus, whereas in Sorbus, the upper leaves were also involved. By repeated pulse applications to selected leaves, temporal profiles of ¹¹C transport were followed on individual plants from April to October. Early in the season, within 2 h after pulse labelling, 30–40% of the fixed radiolabel was exported from leaves in Fraxinus and about 20% in Sorbus. Thereafter export started to decline, particularly in Fraxinus, and the distribution of radiolabel between stem and roots could alter depending on the position of the feed leaf. Speeds of translocation obtained along the rachis and stem showed high variability, but they did not necessarily slow down before the end of the season. The speeds monitored at the rachis of Fraxinus leaves (30–75 cm h^?1) were generally lower than those found on Sorbus (50–130 cm h^?1). As reported in the literature, the two tree species translocate different carbohydrates and show remarkable differences in the ultrastructure of their vascular systems. In that context it is interesting that the temporal profiles of ¹¹C radioactivity obtained from F. excelsior and S. aucuparia could clearly be distinguished by their characteristic shapes. The results are discussed in terms of anatomical characteristics of the conducting tissues and possible differences in phloem loading.     

Incidence of allergenic pollen of Acer spp., Fraxinus spp. and Platanus spp. in the city of La Plata, Argentina: preliminary results

This work studies the airborne pollenconcentrations of Acer spp.,Fraxinus spp. and Platanus spp. sincethe pollen of these three taxa has beencharacterized as etiological agents ofpollinosis. These tree species are present inlarge amounts in the streets of La Plata city.The aeropalynological monitoring was performedwith a Hirst-type spore trap (Lanzoni VPPS,2000). The emission period of the three taxaextends from approximately late August to October.The maximum cumulative totalof arboreal pollen was found to be 30824.7from September 12 to 18. This period coincideswith the peak of total pollen concentration.Pollen grains trapped were analysed andexpressed as daily averages of 5-hour bandsper day during the whole year. Maximum pollenconcentration was registered between 10 a.m.and 2 p.m. During the studied period, 67 patients examinedat the Allergy Service of ``Hospital Interzonalde Agudos R. Rossi' (La Plata) showed allergicdisease. These allergenic episodes may beproduced by the large amount of pollen trees inthe city area.     

Lichen diversity and red-listed lichen species relationships with tree species and diameter in wooded meadows

This study provides a unique large dataset of total epiphytic lichen diversity (fruticose, foliose and crustose species) and composition on 1,294 trees of 17 tree species in wooded meadows in Sweden and Estonia, the Baltic region. The inventory (25,380 observations and 246 lichen taxa) clearly illustrated that Ulmus minor, Quercus robur and Fraxinus excelsior contributed most significantly to epiphytic lichen richness and number of red-listed species. In Sweden, average single tree α richness was 22.2 on Ulmus (only in Sweden), 21.6 on Quercus (25.0 in Estonia) and 19.8 on Fraxinus (16.7 in Estonia), respectively. Ulmus hosted on average one red-listed species per tree, compared with 0.7 on Fraxinus (0.6 in Estonia), 0.4 on Quercus (0.7 in Estonia) and only 0.05 on Betula (same in Estonia). Lichen species composition and the average number of red-listed lichens were influenced by tree diameter on Fraxinus and Quercus, whilst no such pattern was evident on Ulmus. Randomized species accumulation curves of the dominating tree species illustrated that Fraxinus, Quercus and Ulmus supported α dominated lichen communities where individual trees hosted a substantial part of the total richness. Betula, on the other hand, supported β dominated communities where individual trees tended to be dissimilar and, therefore, more of the total richness existed as species turnover among host trees. Lichen species composition was influenced by tree species, and most notably, lichen species on Ulmus had a strong consistent clumping in ordination graphs, with many rare and red-listed lichens. The broadleaved deciduous trees within the wooded meadows clearly contribute greatly to the biodiversity of the Baltic region.     

The effect of climate conditions on inter-annual flowering variability monitored by pollen traps below the canopy in Draved Forest, Denmark

Since 1967 annual pollen deposition has been monitored in the semi-natural mixed deciduous woodland Draved Forest by the Geological Survey of Denmark. In this paper, we analyse the variability in pollen accumulation rates for the eight most common deciduous trees, and their relationships to monthly temperature and precipitation. High summer temperatures in the year before flowering have a positive effect on pollen deposition for several species. A positive correlation between temperatures during the flowering season and pollen accumulation rates is found for Fagus sylvatica, Quercus robur, Fraxinus excelsior and Corylus avellana. The amount of precipitation can have both positive and negative effects on pollen accumulation, depending on species and on time of year. Linear modelling showed that combinations of monthly climate parameters could explain between 10 and 80% of the variation observed in different species. There were marked differences in the time series of pollen accumulation and pollen/climate relationships for some species between traps within the forest related to the location of trees near the traps. This underlines the importance of using multiple traps in a region for this type of study. Time series analyses were used to test for cyclicity in pollen accumulation rates, which could be caused by resource limitations or internal biological factors. No significant autocorrelations were found, although Alnus glutinosa showed a tendency towards 3-year cyclicity. These results indicate that, with the possible exception of Alnus glutinosa, temperature and precipitation are the main factors controlling the annual variability in pollen deposition of the trees in Draved Forest.     

Comparison between Urticaceae (Parietaria) pollen count and hay fever symptoms: assessment of a «threshold-value»

Summary A comparison betweenParietaria pollen count and allergic symptoms of rhino-conjunctivitis in the early season was used in utilized to determine a «threshold-value» for this pollen. Clinical data were obtained from diary-cards of 34 allergic patients and pollen data from a volumetric sampling, carried out by means of a Hirst-Burkard pollen-trap. A significant correlation (r=0.98) was found between pollen count and symptom scores. Mild symptoms were registered with concentrations above 10–15 pollens/m³. Severe symptoms occurred when pollen count exceeded 80/m³/24 h., and over 90% of patients recorded symptoms. The importance of the late reactions and of the total allergenic airborne content are emphasized.     

Pinus pollen season trend in South Spain

In Andalusia (southern Spain), Pinus species are found in mountainous areas and nature reserves, though some species are also grown as ornamentals in cities. Annual airborne pollen trends are regarded as an indicator of variations in climate prompted by overall climate change. Airborne pollen concentration also provides a useful tool for analyzing alterations in the distribution of vegetation in response to environmental factors and to changes in land use. The present study analyzed the Pinus pollen season over 22 years (1993–2014) in 4 Andalusian cities (Córdoba, Granada, Jaén, and Málaga), and examined correlations between airborne pollen concentrations and meteorological parameters (temperature and rainfall). Pinus pollen season lasted from March to June, starting first in Málaga and later in eastern Andalusia. Differences between the pollen curves for each city were attributable to differing proportions of pine species in each province. Temperatures during the months prior to flowering tended to fall, prompting delayed onset of the pollen season in most cities. No significant results were observed for rainfall patterns in most cities. Total pollen concentrations increased at most sites, suggesting that the recorded decline in pine-nut output was not influenced by flowering rates, but to the impact of a local pest.     

Use of <Emphasis Type="Italic">Quercus ilex</Emphasis> subsp. <Emphasis Type="Italic">ballota</Emphasis> phenological and pollen-production data for interpreting <Emphasis Type="Italic">Quercus</Emphasis> pollen curves

Although aerobiological data are often used in phenological research as an indicator of flowering, airborne pollen concentrations are influenced by a number of factors that could affect pollen curves. This paper reports on a study of various aspects of reproductive biology in Q. ilex subsp. ballota, together with environmental factors influencing pollen release and transport, with a view of achieving reliable interpretation of Quercus pollen curves in Ourense (NW Spain). Aerobiological data were recorded from 2002 to 2004 at two sites in the province of Ourense. From 1st February to the end of the flowering period, phenological observations were carried out on 19 trees from the Q. ilex subsp. ballota population found in the Ourense area. Pollen production was calculated for the same trees. The chilling and heating requirements for triggering development were also calculated. The mean flowering period lasted 11-15 days. Reduced pollen output per catkin and, especially, a reduced number of catkins per tree in 2003 and 2004, prompted a marked decline in overall pollen production. Major differences observed in Q. ilex subsp. ballota pollen curves were attributed to the considerable influence both of weather conditions during pollination and pollen production. In years with high pollen production and weather conditions favouring pollen release, Q. ilex subsp. ballota contributed almost 10% to the total Quercus pollen curve. Around 20% of the pollen trapped was captured before or after flowering periods.     

Airborne pollen and spores monitoring in Buenos Aires City: a preliminary report. Part I. Trees and shrubs (AP)

Summary The monthly trees and shrubs pollen (AP) content of the atmosphere during a whole annual period is analyzed. Thirty airborne pollen types have been identified. Most of them come from cultivated plants flowering in late winter-early spring. Thereby the annual peak is recorded in October. The highest frequencies recorded are those ofFraxinus americana, Acer negundo, Platanus spp. andMorus nigra. A second minor peak is recorded in March, and is mainly due toCasuarina spp./Myrica spp. pollen. Aeropalynological data are discussed and correlated with phytogeographical, phenological and meteorological parameters.     

Airborne pollen grains in Nsukka,Nigeria

A study of the airborne pollen grains in Nsukka, Nigeria, has been carried out at two different sampling heights (1.8?m and 15?m) from February 1993 to January 1994. Twenty‐six plant families (40 genera) were identified at the lower sampling height, whilst thirty‐eight families (58 genera) were identified at the height of 15?m. A total of nine and eighteen fern spore types were observed at 1.80?m and 15?m, respectively. The quantitative results indicate that the number of pollen observed at 15?m sampling height was statistically different (p<0.05) from that observed at the height of 1.80?m. The analysis of airborne pollen grains indicates three different periods: (1) dry season, (2) rainy season, and (3) late rainy season to early dry season/Harmattan. The highest pollen abundance was recorded during the late rainy season – early dry season/Harmattan followed by that of the dry season. The predominant pollen grains and fern spores trapped at both heights include Poaceae, Casuarina equisetifolia, Milicia excelsa, Elaeis guineensis, Celtis integrifolia, Alchornea cordifolia, Amaranthaceae/Chenopodiaceae, Combretaceae/Melastomataceae, Nephrolepis biserrata, Thelypteris totta, and Dryopteris spp.     

Phenological records as a complement to aerobiological data

Phenological studies in combination with aerobiological studies enable one to observe the relationship between the release of pollen and its presence in the atmosphere. To obtain a suitable comparison between the daily variation of airborne pollen concentrations and flowering, it is necessary for the level of accuracy of both sets of data to be as similar as possible. To analyse the correlation between locally observed flowering data and pollen counts in pollen traps in order to set pollen information forecasts, pollen was sampled using a Burkard volumetric pollen trap working continuously from May 1993. For the phenological study we selected the main pollen sources of the six pollen types most abundant in our area: Cupressaceae, Platanus, Quercus, Plantago, Olea, and Poaceae with a total of 35 species. We selected seven sites to register flowering or pollination, two with semi-natural vegetation, the rest being urban sites. The sites were visited weekly from March to June in 2007, and from January to June in 2008 and 2009. Pollen shedding was checked at each visit, and recorded as the percentage of flowers or microsporangia in that state. There was an association between flowering phenology and airborne pollen records for some of the pollen types (Platanus, Quercus, Olea and Plantago). Nevertheless, for the other types (Cupressaceae and Poaceae) the flowering and airborne pollen peaks did not coincide, with up to 1 week difference in phase. Some arguments are put forward in explanation of this phenomenon. Phenological studies have shown that airborne pollen results from both local and distant sources, although the pollen peaks usually appear when local sources are shedding the greatest amounts of pollen. Resuspension phenomena are probably more important than long-distance transport in explaining the presence of airborne pollen outside the flowering period. This information could be used to improve pollen forecasts.     

An annual study of airborne pollen in northern Mexico City

An investigation of airborne pollen in northern Mexico City was carried out for one year. A total of 24 taxa were identified and classified according to the growing form in pollen of trees, weeds and grasses. Pollen grains were recorded all year round with a peak in December. The trees group showed the highest quantity of pollen as well as taxa diversity, although its peak period was in the dry season. The weeds and grasses emitted a larger quantity of pollen in the rainy season. The dominant taxa wereAlnus, Casuarina, Compositae and Gramineae. As for their relation with meteorological parameters, we found that the increase of pollen concentration was related to high temperatures, low relative humidity and high wind speed, the latter causing an increase of airborne pollen with no dilution at all. The hours with the highest pollen concentration where from 16:00 to 18:00.     

An annual study of airborne pollen in northern Mexico City

An investigation of airborne pollen in northern Mexico City was carried out for one year. A total of 24 taxa were identified and classified according to the growing form in pollen of trees, weeds and grasses. Pollen grains were recorded all year round with a peak in December. The trees group showed the highest quantity of pollen as well as taxa diversity, although its peak period was in the dry season. The weeds and grasses emitted a larger quantity of pollen in the rainy season. The dominant taxa wereAlnus, Casuarina, Compositae and Gramineae. As for their relation with meteorological parameters, we found that the increase of pollen concentration was related to high temperatures, low relative humidity and high wind speed, the latter causing an increase of airborne pollen with no dilution at all. The hours with the highest pollen concentration where from 16:00 to 18:00.     

Comparative study of different methods for capturing airborne pollen,and effects of vegetation and meteorological variables

The atmosphere of Mar del Plata city (Argentina) was monitored using three different pollen traps—Burkard, Rotorod, and Tauber—during a flowering season (mid-winter to springtime) in order to compare the diversity and amounts of pollen grains collected in each trap. Sixty three percent of taxa diversity was simultaneously recorded by all three apparatuses. The five most abundant types of pollen in the three traps were Platanus, Ulmus, Quercus, Poaceae, and Fraxinus. The Tauber trap contained the most pollen from taxa with the largest grains, and exclusively trapped ten pollen types with entomophilous characteristics. The amount of pollen in each trap and local/extra-local plant abundance were compared to elucidate the effect of the method used on the pollen–vegetation relationship. The correlation coefficients for total pollen were positive and significant between all pairs of traps. The maximum peak was observed first in the Burkard trap, in agreement with an increase in temperature, but the general pattern in the three traps was similar, with a maximum in early spring. Opposite deviations from the mean value were observed for the Burkard and Tauber data; these deviations were associated negatively with wind speed and relative humidity, respectively. This paper discusses whether in some cases the pollen records could be used in an equivalent manner, although with some limitations.     

Airborne conifer pollen grains are rarely deposited on stigmas of coflowering insect‐pollinated angiosperms

Although plant species with either animal or wind pollination modes are widespread and usually sympatric in nature, the degree of pollen interference from wind‐pollinated species on animal‐pollinated species remains little known. Conifer trees generally release a huge number of pollen grains into the air, floating into our noses and sometimes causing an allergic response. Here we document airborne pollen from two conifers (Pinus densata Mast. and Picea likiangensis (Franch.) E. Pritz.) deposited on the stigmas of eight coflowering insect‐pollinated angiosperms over 2 years in a mountainous forest community, in Shangri‐La, southwest China. Pollen density in the air as well as conifer pollen deposited onto stigmas at short and long distances from the airborne pollen source were quantified. Our results showed that conifer pollen as a proportion of total stigmatic pollen loads in the insect‐pollinated plants varied from 0.16% to 8.67% (3.16% ± 0.41%, n = 735) in 2016 and 0.66% to 5.38% (2.87% ± 0.86%, n = 180), and pollen quantity per unit area was closely related to that of airborne pollen in the air. Conifer pollen deposition on stigmas of insect‐pollinated species decreased greatly with increased distance from the pollen source. In the 10 plant species flowering in summer after conifer pollen release had finished, heterospecific pollen deposited on these stigmas came mainly from other insect‐pollinated flowers, with little contribution from airborne conifer pollen. The results indicate that there might be little interference with coflowering angiosperms by airborne pollen from dominant conifers in natural communities.     

Study of the floral phenology of <Emphasis Type="Italic">Olea europaea</Emphasis> L. in Jaén province (SE Spain) and its relation with pollen emission

Phenological and aerobiological studies provide important information regarding the reproductive biology of cultivated species such as the olive. This article presents the results of an exploratory study of the floral phenology of Olea europaea L. at different altitudes in Jaén province (SE Spain) and an analysis of the main meteorological factors affecting flowering. As well, this study aimed to detect the relationship between phenology and olive pollen emission as a means of interpreting Olea pollen curves in the city of Jaén. Phenological observations were performed on olive trees at six sites, each at different altitudes and distributed over the whole area of olive cultivation in the province. Pollen data were obtained using a Hirst-type volumetric spore trap located within the city of Jaén. Phenological and aerobiological data were recorded in 2006 and 2007. This study shows that the chronology of the start of the flowering period depends on altitude. Statistical analyses indicate that the temperature, humidity, cumulative rainfall and cumulative solar radiation are the meteorological parameters that most affect olive floral phenology. The pollen season in Jaén generally lasts from May to June, with an annual total emission of over 40,000 pollen grains, the highest annual level of olive pollen emission in the world. The airborne pollen concentrations recorded in the city of Jaén are above all influenced by the olive groves located in the Guadalquivir valley.     

Airborne‐pollen pool and mating pattern in a hybrid zone between Pinus pumila and P. parviflora var. pentaphylla

The reproductive isolation barriers and the mating patterns among Pinus pumila, P. parviflora var. pentaphylla and their hybrids were examined by flowering phenology and genetic assays of three life stages: airborne‐pollen grains, adults and seeds, in a hybrid zone on Mount Apoi, Hokkaido, Japan. Chloroplast DNA composition of the airborne‐pollen was determined by single‐pollen polymerase chain reaction. Mating patterns were analysed by estimating the molecular hybrid index of the seed parent, their seed embryos and pollen parents. The observation of flowering phenology showed that the flowering of P. pumila precedes that of P. parviflora var. pentaphylla by about 6 to 10 days within the same altitudinal ranges. Although this prezygotic isolation barrier is effective, the genetic assay of airborne‐pollen showed that the two pine species, particularly P. pumila, still have chances to form F₁ hybrid seeds. Both parental species showed a strong assortative mating pattern; F₁ seeds were found in only 1.4% of seeds from P. pumila mother trees and not at all in P. parviflora var. pentaphylla. The assortative mating was concluded as the combined result of flowering time differentiation and cross‐incompatibility. In contrast to the parental species, hybrids were fertilized evenly by the two parental species and themselves. The breakdown of prezygotic barriers (intermediate flowering phenology) and cross‐incompatibility may account for the unselective mating. It is suggested that introgression is ongoing on Mount Apoi through backcrossing between hybrids and parental species, despite strong isolation barriers between the parental species.     

Influence of meteorological parameters on Olea flowering date and airborne pollen concentration in four regions of Portugal

For calculating the total annual Olea pollen concentration, the onset of the main pollen season and the peak pollen concentration dates, using data from 1998 to 2004, predictive models were developed using multiple regression analysis. Four Portuguese regions were studied: Reguengos de Monsaraz, Valença do Douro, Braga and Elvas. The effect of some meteorological parameters such as temperature and precipitation on Olea spatial and temporal airborne pollen distribution was studied. The best correlations were found when only the pre‐peak period was used, with thermal parameters (maximum temperature) showing the highest correlation with airborne pollen distribution. Independent variables, selected by regression analysis for the predictive models, with the greatest influence on the Olea main pollen season features were accumulated number of days with rain and rainfall in the previous autumn, and temperatures (average and minimum) from January through March. The models predict 59 to 99% of the total airborne pollen concentration recorded and the initial and peak concentration dates of the main Olea pollen season.