The arboreal vegetation of the Central Negev Highlands, Israel, at the end of the Pleistocene: Evidence from archaeological charred wood remains

Charcoal assemblages from five Terminal Pleistocene sites in the Central Negev Highlands, Israel, have been analyzed. Eleven taxa have been identified, two of which, juniper andPaliurus, no longer grow in this district, and one,Pinus (of which only a single occurrence was encountered), is considered intrusive, and the rest are taxa which still characterize the region today. Among these latter,Pistacia atlantica (which is the dominant tree in this area today) was the most common. Association of juniper andPaliurus is found today only in the northern Near East. It can not be ascertained that such an association characterized the Central Negev Highlands throughout the entire period spanned by the charcoal assemblages, since it is possible thatPistacia atlantica may have become temporarily extinct. In any case the former occurrence of juniper and particularlyPaliurus in the Central Negev Highlands clearly point to higher humidity in this region during the final stages of the Pleistocene. This conclusion is corroborated by a variety of proxy climatic indicators throughout the southern Levant.     

A combined light and scanning electron microscopy study

The uppermost Eocene Florissant Formation, Rocky Mountains, Colorado, has yielded numerous insect, vertebrate and plant fossils. Three previous comprehensive palynological studies investigated sections of lacustrine deposits of the Florissant Formation and documented the response of plant communities to volcanic eruptive phases but overall found little change in plant composition throughout the investigated sections. These studies reported up to 150 pollen and spore phenotypes. In the present paper, we used a taxonomic approach to the investigation of dispersed pollen and spores of the Florissant Formation. Sediment samples from the shale units containing macrofossils were investigated using light microscopy (LM) and scanning electron microscopy (SEM). The general picture of the palynoflora is in agreement with previous studies. However, the combined LM and SEM investigation provides important complementary information to previous LM studies. While a fairly large amount of previous pollen determinations could be confirmed, the purported taxonomic affinities of several pollen phenotypes need to be revised. For example, pollen referred to as Podocarpus or Podocarpidites sp. belongs to the Pinaceae Cathaya, Malus/Pyrus actually belongs to Dryadoideae, pollen of the form genus Boehlensipollis referred to as Proteaceae/Sapindaceae/Elaeagnaceae or Cardiospermum belongs to Sapindaceae but not to Cardiospermum, and pollen of Persicarioipollis sp. B with previously assumed affinities to Polygonaceae actually belongs to Thymelaeaceae. Pandaniidites and one type of Malvacipollis cannot be linked with Pandanaceae and Malvaceae. A few taxa are new records for Florissant (Ebenaceae: Diospyros; Mernispermaceae; Trochodendraceae: Tetracentron). In general, SEM investigations complement the LM palynological studies and improve the identification of dispersed pollen and spores and enable integration of data from dispersed fossil pollen into a wide range of comparative morphological, taxonomic, evolutionary, biogeographic and phylogenetic studies.     

PALYNOLOGY AND SYSTEMATICS OF CUPHEA (LYTHRACEAE). I. MORPHOLOGY AND ULTRASTRUCTURE OF THE POLLEN WALL

A survey of pollen from 153 species of Cuphea has revealed a remarkable array of morphological forms. The survey involved light and electron microscope investigations of C. crassiflora, jorullensis, and koehneana to determine details of exine morphology, and a more general study of pollen from an additional 150 species. Comparison of pollen types within a single morphological category and within taxonomic groups (i.e., sections or subsections) indicates considerable variation at subgeneric levels. The genus is distinctly eurypalynous, and the extent to which pollen varies among the sections, subsections, species and varieties is probably exceeded by few genera of comparable size. The pollen is also variable within each taxon, but size studies of single-anther lactic acid preparations demonstrate the genus is not polymorphic, as in Lythrum, where pollen polymorphism is associated with heterostyly. The latter phenomenon is as yet unknown in Cuphea. These results reveal that pollen morphology constitutes an important and useful character for taxonomic studies of Cuphea.     

Optimization of conditions for germination of cold-stored <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> pollen

One of the rare weak points of the model plant Arabidopsis is the technical problem associated with the germination of its male gametophyte and the generation of the pollen tube in vitro. Arabidopsis pollen being tricellular has a notoriously low in vitro germination compared to species with bicellular pollen. This drawback strongly affects the reproducibility of experiments based on this cellular system. Together with the fact that pollen collection from this species is tedious, these are obstacles for the standard use of Arabidopsis pollen for experiments that require high numbers of pollen tubes and for which the percentage of germination needs to be highly reproducible. The possibility of freeze-storing pollen after bulk collection is a potential way to solve these problems, but necessitates methods that ensure continued viability and reproducible capacity to germinate. Our objective was the optimization of germination conditions for Arabidopsis pollen that had been freeze-stored. We optimized the concentrations of various media components conventionally used for in vitro pollen germination. We found that in general 4 mM calcium, 1.62 mM boric acid, 1 mM potassium, 1 mM magnesium, 18% sucrose at pH 7 and a temperature of 22.5°C are required for optimal pollen germination. However, different experimental setups may deviate in their requirements from this general protocol. We suggest how to optimally use these optimized methods for different practical experiments ranging from morphological observations of pollen tubes in optical and electron microscopy to their bulk use for molecular and biochemical analyses or for experimental setups for which a specific medium stiffness is critical. F. Bou Daher and Y. Chebli contributed equally to this study.     

The pollination biology ofHibbertia stricta (Dilleniaceae)

The exines of pollen grains ofHibbertia stricta (DC.)R. Br. exF. Muell. (Sect.Pleurandra) wear an oily, yellow pollen coat that stains positively for lipids. The pollen is collected by asocial bees, exclusively. The most common floral foragers are members of the genusLasioglossum (subgenusChilalictus;Halictidae) and they harvest pollen via thoracic vibration. As these bees cling to the inflated anthers their pollen smeared bodies come in contact with either of the two wet, nonpapillate stigmas. The stigmas respond positively to cytochemical tests for the presence of esterase immediately following expansion of the corolla, indicating the effective pollination period. The foraging patterns of the bees are narrowly to broadly polylectic. AsH. stricta flowers are nectarless, it is not surprising that bees bearing mixed pollen loads always carry the pollen of at least one nectariferous, coblooming plant. The pollination biology ofH. stricta is compared with otherHibbertia spp. and with pollen flowers in general.     

A comprehensive aerobiological study of the airborne pollen in the Irish environment

Respiratory allergies triggered by pollen allergens represent a significant health concern to the Irish public. Up to now, Ireland has largely refrained from participating in long-term aerobiological studies. Recently, pollen monitoring has commenced in several sampling locations around Ireland. The first results of the pollen monitoring campaigns for Dublin (urban) and Carlow (rural) concerning the period 2017–2019 and 2018–2019, respectively, are presented herein. Additional unpublished pollen data from 1978–1980 and, 2010–2011 were also incorporated in creating the first pollen calendar for Dublin. During the monitoring period over 60 pollen types were identified with an average Annual Pollen Integral (APIn) of 32,217 Pollen × day/m³ for Dublin and 78,411 Pollen × day/m³ for Carlow. The most prevalent pollen types in Dublin were: Poaceae (32%), Urticaceae (29%), Cupressaceae/Taxaceae (11%), Betula (10%), Quercus (4%), Pinus (3%), Fraxinus (2%), Alnus (2%) and Platanus (1%). The predominant pollen types in Carlow were identified as Poaceae (70%), Urticaceae (12%), Betula (10%), Quercus (2%), Fraxinus (1%) and Pinus (1%). These prevalent pollen types increased in annual pollen concentration in both locations from 2018 to 2019 except for Fraxinus. Although higher pollen concentrations were observed for the Carlow (rural) site a greater variety of pollen types were identified for the Dublin (urban) site. The general annual trend in the pollen season began with the release of tree pollen in early spring, followed by the release of grass and herbaceous pollen which dominated the summer months with the annual pollen season coming to an end in October. This behaviour was illustrated for 21 different pollen types in the Dublin pollen calendar. The correlation between ambient pollen concentration and meteorological parameters was also examined and differed greatly depending on the location and study year. A striking feature was a substantial fraction of the recorded pollen sampled in Dublin did not correlate with the prevailing wind directions. However, using non-parametric wind regression, specific source regions could be determined such as Alnus originating from the Southeast, Betula originating from the East and Poaceae originating from the Southwest.

     

The pollen season dynamics and the relationship among some season parameters (start,end, annual total,season phases) in Kraków,Poland, 1991–2008

The dynamics of 15 taxa pollen seasons in Kraków, in 1991–2008 was monitored using a Burkard volumetric spore trap of the Hirst design. The highest daily pollen concentrations were achieved in the first half of May, and they were caused mainly by Betula and Pinus pollen. The second period of the high concentrations took place from the middle of July to the end of August (mainly Urtica pollen). Tree pollen seasons were shorter (18–24 days) in comparison with the most herbaceous pollen seasons (73–89 days), except at Artemisia and Ambrosia seasons (30 and 24 days, respectively). The season phases (percentyles) of the spring and late-summer taxa were the most variable in the consecutive years. The highest annual sums were noted for Urtica, Poaceae (herbaceous pollen seasons) and for Betula, Pinus, Alnus (tree pollen seasons), and the highest variability of annual totals was stated for Urtica, Populus, Fraxinus and the lowest for Ambrosia, Corylus, Poaceae. For the plants that pollinate in the middle of the pollen season (Quercus, Pinus and Rumex), the date of the season start seems not to be related to the season end, while for late pollen seasons, especially for Ambrosia and Artemisia, the statistically negative correlation between the start and the end season dates was found. Additionally, for the most studied taxa, the increase in annual pollen totals was observed. The presented results could be useful for the allergological practice and general botanical knowledge.     

BIOSYSTEMATIC STUDIES IN THE BOUTELOUA CURTIPENDULA COMPLEX. III. POLLEN SIZE AS RELATED TO CHROMOSOME NUMBERS

Pollen size statistics are presented for 10 closely related species of Bouteloua and relationships between pollen size and chromosome numbers are presented for 13 populations of 5 species and 3 varieties. With 1 exception, all populations of all taxa conformed to a general pattern of pollen size dependent upon chromosome number. Chromosome numbers varied from 2n = 20 to 2n = ca. 103, with several independent aneuploid series. Statistical analyses were made of pollen size as related to chromosome number in the 3 varieties of B. curtipendula. These data showed that tetraploids (2n = 40) of var. tenuis had significantly greater pollen size and coefficient of variation than diploids (2n = 20) of the same variety. Similarly, aneuploids of var. curtipendula with 2n = 45 to 2n = 64 chromosomes had significantly larger and more variable pollen than tetraploids (2n = 40) of the same variety. Highly significant positive regression coefficients were obtained from analyses of chromosome numbers and mean pollen size, and chromosome numbers and coefficient of variation, for var. curtipendula. Regression coefficients for var. caespitosa populations with chromosome numbers over the hexaploid (2n = 60) level were not significant.     

Temporal pollen pattern in temperate trees: expedience or fate?

European forests are populated with a variety of wind‐pollinated tree species. Their pollen productivity and spatio‐temporal pattern are largely unknown. Long‐term data (17 years) collected at 22 sites across Austria were presented and the pollen production of 12 tree genera was analysed. We ranked the tree genera according to their pollen productivity taking actual tree abundances of the Austrian Forestry Inventory into account. The productivity varied strongly among tree genera with a maximum for Betula. Pollen production in Larix, Abies and Picea amounted to approximately 1/20, while in increasing order Salix, Quercus, Alnus, Populus and Fraxinus produced approximately 1/3 to 1/4 of the respective Betula estimate. In general, pollen quantity in broadleaves was higher than in conifers. We analysed the temporal pollen production pattern by means of hierarchical cluster analysis and identified three major groups: [(Fagus, Larix, Picea, Abies), (Alnus, Betula, Fraxinus)], [Carpinus],[Populus, Salix, Pinus, Quercus]. Distance matrices based on life‐history traits as well as molecular phylogeny were also constructed; they correlated significantly with each other by means of Mantel‐tests. However, there was no significant relationship between the distances on temporal pollen production with the other matrices. Intermittent or idiosyncratic pollen production was studied by means of deviation from expected means, skewness and spindle diagrams. We proposed that Fagus, Carpinus, Larix, Picea and Abies belong to ‘masting pollen producers’, while the remaining genera idiosyncratically produced pollen over the monitored period. Moreover we correlated the distance matrix of pollen production for each tree genus at each sampling site with respective ‘ecological distance matrices’ based on aerial and altitudinal distance among sites. Significant correlations were detected for tree genera (Fagus, Larix, Picea) which were also prone to pollen masting, thus indicating a Moran effect.     

Lack of correlation between pollen aperture number and environmental factors in pansies (Viola L., sect. Melanium Ging.) – pollen heteromorphism re‐examined

• The development of different pollen morphs by one specimen – pollen heteromorphism – occurs in ca. one‐third species of the genus Viola. Melanium section species (pansies) stand out in producing the widest range of apertures among Viola species. Aperture number decreases with elevation increase, and faster germination of five‐aperturate pollen as compared with three‐aperturate has previously been postulated.
• We re‐examined pollen heteromorphism in the context of its viability, and made correlations with elevation (>1500 m a.s.l. versus <1500 m a.s.l.), soil type (metalliferous versus non‐metalliferous; MET versus NMET) and chromosome number based on selected study criteria of ca. 20% karyologically and morphologically strongly differentiated but genetically closely related pansies.
• A total of 79% of analysed species were heteromorphic, forming three‐ to six‐colp or ate pollen per individual flower. Mean aperture number and pollen viability were not affected by soil type (MET versus NMET). Mean aperture number was also not influenced by elevation or species chromosome number. Positive correlations were established between aperture number and pollen viability, negative between pollen viability and elevation (increasing altitude of 100 m decreased pollen viability by 0.4%) and lack of correlation between chromosome number and pollen viability.
• The varied frequencies of different pollen morphs among species are not under the general pressure of ecological conditions, as previously postulated for the species of Melanium section. Rather, this trait in pansies, similar to other floral characters (e.g. long, curved nectar spur, ‘landing platform’, posterior petals with nectar guides), is adaptive but dependent on the breeding system (inbreeding versus outbreeding) of the individual species.

     

Effects of flower number on estimated pollen transfer in natural populations of three hermaphroditic species: an experiment with fluorescent dye

The relationship between the number of open flowers and pollen transfer to stigmas was estimated in three insect-pollinated species (Cynoglossum officinale, Echium vulgare and Oenothera erythrocepala) in 1995 and 1996, using fluorescent dye as a pollen analogue. Dye was applied to an equal number of flowers on a small, a medium and a large individual and its pattern of dispersal to stigmas of conspecifics in local populations was observed. In Cynoglossum officinale and in Echium vulgare large individuals tended to receive more visits per flower. In Oenothera erythrocepala no difference in number of visits per flower was found between small and large individuals. Geitonogamous pollination clearly occurred in all species. In Cynoglossum officinale large individuals transferred more pollen per flower within the same plant (geitonogamy) and an equal or a slightly smaller amount between plants, compared to small individuals. As a result total pollen transfer per flower increased in both years with increasing flower number. In Echium vulgare and in Oenothera erythrocepala large individuals transferred more pollen per flower within the plant (pollen discounting), but a significantly lower amount per flower to other individuals in the populations compared to small individuals. For both these species, there is no difference in total pollen transfer between small and large individuals. In general, the male fitness curve, as estimated by pollen transfer, is a decelerating function of flower number. We discuss this in relation to optimal sex-allocation and the pollen donation hypothesis.     

Botanical and geographical origin of honey from the dry and humid Chaco ecoregions (Argentina)

To characterise the botanical and geographical origin of honey from the Chaco region (Argentina), 189 samples of honey were examined for pollen content using standard methodology. A general feature was the high representation of pollen from native arboreal plants, mainly of Fabaceae and the scarcity of pollen from herbaceous plants. One hundred and twenty-three samples proved to be unifloral. The most common were from: Prosopis alba, Helianthus annuus, Sarcomphalus mistol, Eugenia uniflora and Schinopsis balansae followed by those of Copernicia alba, Trithrinax schizophylla, Tessaria integrifolia, Baccharis-Eupatorium, Cynophalla retusa, Schinopsis lorentzii, Gleditsia amorphoides, Heimia salicifolia, Pisonia zapallo, Sagittaria montevidensis and Bulnesia sarmientoi. The pollen spectrum allowed the Dry and Humid Chaco ecoregions to be distinguished. The presence of pollen from cultivated crops and naturalised plants reflects a transitional complex between both ecoregions.     

Automated pollen recognition using 3D volume images from fluorescence microscopy

Identifying and counting of pollen grains in ambient air samples is still a demanding and time-consuming task even for an experienced microscopist. This article describes a technique which may be employed to establish a fully automated system for this task. Based on a 3D volume fluorescence image of a pollen grain taken with a confocal laser scanning microscope, the described system is able to recognize the pollen taxa. The system autonomously extracts all required information for the recognition from a data base with reference objects (self-learning system) and only needs to calculate very general purpose features of the volumetric data sets (so-called gray scale invariants). This allows for easy adaptation of the system to other conditions (e.g., pollen of a special area) or even other objects than pollen (e.g., spores, bacteria etc.) just by exchanging the reference data base. When using a reference data base with the 26 most important German pollen taxa, the recognition rate is 92%. With a special database for allergic purposes recognizing only Corylus, Alnus, Betula, Poaceae, Secale, Artemisia and ``allergically non-relevant' the recognition rate is 97.4%.     

Division of the generative nucleus in cultured pollen tubes of the Bromeliaceae

Pollen germination, division of the generative nucleus and position of the generative nucleus in the pollen tube during in vitro germination were examined for six bromeliad cultivars. The influence of mixed amino acids (casein hydrolysate) and individual amino acids (Arg, Asn, Asp, Glu, Gly, Met, Phe, Orn, Tyr) were tested. Aechmea fasciata and A. chantinii pollen tubes showed more generative nuclear division in cultured pollen tubes than the other four cultivars tested. Casein hydrolysate did not stimulate generative nuclear division. In general arginine (1 mM) improved division of the Aechmea generative nucleus and to a lesser extent this of Vriesea `Christiane', Guzmania lingulata and Tillandsia cyanea. A concentration of 2 mM arginine reduced pollen tube growth of Aechmea. The vegetative nucleus was ahead of the generative nucleus in approximately 50% of the pollen tubes of all cultivars studied. In about 25% of the pollen tubes, the generative nucleus was ahead and in ±25% pollen tubes the vegetative and generative nuclei were joined together. The distance between the two generative nuclei and the distance from the generative nuclei to the pollen tube tip differed significantly for Aechmea fasciata and A. chantinii. The influence of different amino acids for Aechmea fasciata and A. chantinii varied with respect to pollen germination and generative nuclear division. Arg and Met improved nuclear division of both Aechmea cultivars. Pollen germination and sperm cell production were not linked. This information is important to ameliorate in vitro pollination methods used to overcome fertilization barriers in Bromeliaceae and other higher plants.     

Pollen size in Carex: The effect of different chemical treatments and mounting media

Pollen size and pollen aperture size for ten species of the genus Carex L., native to Estonia, have been measured using light microscopy. The species selected represent different sections of the genus, a range of habitats and different chromosome numbers. The effects of two basic chemical treatments, two mounting media and the effect of chemically induced dehydration with tertiary butyl alcohol (TBA) on the size of pollen grains were then recorded.

In general pollen size and pollen aperture size of the species examined is highly variable at both intraspecific and interspecific levels. Carex hirta has notably larger pollen grains than any of the other species investigated and, although correlations between size and chromosome number in the species examined are limited, it also has the highest chromosome number. Statistically significant size differences resulted from variations in chemical treatment, mounting media and tertiary butyl alcohol (TBA) induced dehydration. Acetolysed pollen grains are larger than potassium hydroxide (KOH) treated pollen grains. Pollen grains dehydrated after chemical treatment with TBA are larger than pollen grains not dehydrated. Pollen grains mounted in silicon oil are smaller than grains mounted in glycerine. But considering the great size variation of Carex pollen grains, the size changes caused by preparation procedures fall within the size variation range of the species examined.

All the samples contained a high number of deformed pollen grains and pollen grains with hardly distinguishable or no lateral apertures.     

Diurnal patterns of airborne pollen concentration of the selected tree and herb taxa in Gdańsk (northern Poland)

The diurnal variation of airborne pollen concentrations of Alnus, Betula, Pinus, Poaceae, Urtica and Artemisia was examined at the sampling station in Gdańsk, northern Poland. Diurnal patterns of Alnus and Pinus pollen show distinctly lower values and low frequency of diurnal maxima between midnight and late morning and a clear rise of pollen counts at around noon. The rather high values remain during the afternoon and evening. The Betula pollen counts are almost evenly distributed along day and night and diurnal maxima appear in similar frequency at any time of day. Pollen concentrations of Poaceae increase at about 9.00 hours and remain high till late evening. Diurnal patterns of Urtica and Artemisia show very clear variation with high peaks at around 9.00 hours (Artemisia) and 13.00 hours (Urtica). The comparison of the data from Gdańsk with the data from other aerobiological stations shows very similar general features in the diurnal patterns irrespective the region or the local situation.     

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.     

Exine ultrastructure of in situ peltasperm pollen from the Rhaetian of Germany and its implications

Morphology and exine ultrastructure of pollen grains of Triassic peltasperms have been studied for the first time. Pollen grains of Antevsia zeilleri from the Rhaetian of Germany are of the Cycadopites-type and monosulcate; the sculpturing is the same in the apertural and non-apertural areas. The proximal exine includes a row of lacunae covered by a solid, thick tectum and underlined by a foot layer. Pillars are hanging from the tectum between the lacunae. The exine is thinning to a homogeneous layer in the apertural region. The latter is bordered by thicker alveolate areas of the exine, in places resembling a saccus-like ultrastructure. The endexine includes white-line-centred lamellae. The exine ultrastructure is compared with that of pollen of Permian peltasperms. Although pollen types ascribed to Permian peltasperms are completely different in their general morphology, a transformation can be hypothesized by ultrastructural data from Permian Vesicaspora into Triassic Cycadopites extracted from pollen sacs of Antevsia. Comparison with Cycadopites of non-peltaspermalean (Ginkgoalean, Cycadophyte) and unknown affinities has been accomplished. The exine ultrastructure is distinctive enough to differentiate among peltaspermalean, cycadalean and bennettitalean Cycadopites; some ultrastructural features are shared with pollen of modern Ginkgo biloba. More ultrastructural data are needed as well as numerous sections of pollen grains are necessary to reveal original unchanged ultrastructure.     

TRACKING POLLEN FLOW OF SOLANUM ROSTRATUM (SOLANACEAE) USING BACKSCATTER SCANNING ELECTRON MICROSCOPY AND X-RAY MICROANALYSIS

A technique using micronized metal powders was developed for both general labeling of pollen and marking of individual pollen grains. After labeling, pollen flow is analyzed by the use of backscatter scanning electron microscopy and X-ray microanalysis. To test the efficiency and efficacy of the technique, we assessed differences in pollen distribution in Solanum rostratum, an enantiostylous species with dimorphic anthers which are putatively feeding and pollinating anthers. Pollen from each set of anthers was labeled using different micronized metal powders. We could not confirm the differentiation of functional anthers in S. rostratum. This technique provides an efficient and convenient method for tracking pollen movement within and between flowers, and anthers within a single blossom can be differentially marked.