D. Vokou

Changes to Airborne Pollen Counts across Europe

A progressive global increase in the burden of allergic diseases has affected the industrialized world over the last half century and has been reported in the literature. The clinical evidence reveals a general increase in both incidence and prevalence of respiratory diseases, such as allergic rhinitis (common hay fever) and asthma. Such phenomena may be related not only to air pollution and changes in lifestyle, but also to an actual increase in airborne quantities of allergenic pollen. Experimental enhancements of carbon dioxide (CO) have demonstrated changes in pollen amount and allergenicity, but this has rarely been shown in the wider environment. The present analysis of a continental-scale pollen data set reveals an increasing trend in the yearly amount of airborne pollen for many taxa in Europe, which is more pronounced in urban than semi-rural/rural areas. Climate change may contribute to these changes, however increased temperatures do not appear to be a major influencing factor. Instead, we suggest the anthropogenic rise of atmospheric CO levels may be influential.

Effects of aromatic plants on potato storage: sprout suppression and antimicrobial activity

Abstract Sprout suppressant properties of the essential oils of Lavandula angustifolia (lavender), Mentha pulegium (mint), Mentha spicata (spearmint), Origanum onites (Turkish oregano), Origanum vulgare ssp. hirtum (Greek oregano), Rosmarinus officinalis (rosemary), and Salvia fruticosa (sage) were assessed. Except for oregano oils, all other essential oils suppressed potato sprout growth. Those of L. angustifolia, Salvia frucicosa and R. officinalis were the most effective. Application of crude herbs, instead of extracted essential oils, lead to comparable results. The inhibition is reversible, thus allowing subsequent normal sprouting of seed potatoes. The essential oils of the above mentioned aromatic plants, as well as those of Coridothymus capitatus (Spanish oregano), Origanum dictamnus (Cretan dittany), and Satureja thymbra , were also found to possess potent antimicrobial activities against Erwinia carotovora strains and bacteria isolated from the surface of potato tubers. The carvacrol-containing essential oils, and particularly that of Greek oregano, had the strongest effect. Use of aromatic plants could be an effective and safe way to prolong the storage life of potato tubers, at the same time protecting them from certain microbial attacks. This holds, in particular, for regions such as the Mediterranean, where prolongation of tuber dormancy needs more drastic and costly measures, because of the high temperatures. As aromatic plants grow natively and in abundance, their use would be cost-effective.

Mentha spicata (Lamiaceae) chemotypes growing wild in Greece

Mentha spicata is the commonest mint species growing wild in Greece, exhibiting great morphological and chemical variability. The oil content from different wild populations examined ranged from 0.3% to 2.2%; the most common value being ca.1%. Though commercially exploited M. spicata plants are always rich in carvone and dihydrocarvone, wild populations are very variable; four different chemotypes were distinguished within the species. These chemotypes are characterized by the high contribution of the following compounds: (1) linalool, (2) piperitone oxide or piperitenone oxide, (3) carvone-dihydrocarvone and (4) pulegone-menthone-isomenthone. This chemical variability suggests the possibility of further developing and exploiting the full potential of the species.

Activation of soil respiration and shift of the microbial population balance in soil as a response to Lavandula stoechas essential oil.

Lavandula stoechas, a native plant of Greece, is rich in essential oil and fenchone is its major constituent. We examined the effect of the essential oil and its main constituents on soil metabolism and microbial growth. Addition of the essential oil or fenchone to soil samples induced a remarkable increase in soil respiration. This was accompanied by an increase in the soil bacterial population of three orders of magnitude. This sizable population was not qualitatively similar to that of the control soil samples. One bacterial strain dominated soil samples treated with L. stoechas essential oil or fenchone. By use of the disk diffusion assay, we evaluated the capacity of three bacterial strains that we isolated from the soil samples, as well as Escherichia coli and Bacillus subtilis (reference strains), to grow in the presence of the essential oil and three of its main constituents (fenchone, cineol, α-pinene). The substances tested did not inhibit the growth of the strain found to dominate the bacterial populations of treated soil samples; they severely inhibited B. subtilis. The other two isolated strains could also grow in liquid cultures in the presence of different quantities of essential oil or fenchone. Addition of fenchone at the end of the exponential phase increased the cell numbers of the strain that dominated the bacterial populations of treated soil samples, indicating use of the substrate added. On the basis of these results, we propose a scheme of successional stages during the decomposition process of the rich-in-essential-oil litter of aromatic plants that abound in the Mediterranean environment.

EFFECTS OF VOLATILE OILS FROM AROMATIC SHRUBS ON SOIL MICROORGANISMS

Abstract Volatile oils from Thymus capitatus, Satureja thymbra and, to a lesser extent, Rosmarinus officinalis stimulate soil respiration. The S. thymbra oil is fungistatic to the germination of Penicillium citrinum spores in soil, and to mycelial growth of Mucor hiemalis in liquid culture. Addition of the S. thymbra oil and, to a lesser extent, R. officinalis oil to soil result in increased bacterial numbers. Bacteria appear to use the oils as carbon and energy sources. Thus the oils appear to have an ecological effect by shifting the soil population balance from fungi to bacteria.

The Onset, Course and Intensity of the Pollen Season

The onset, duration and intensity of the period when pollen is present in the air varies from year to year. Amongst other things, there is an effect upon the quality of life of allergy sufferers. The production and emission of pollens are governed by interacting environmental factors. Any change in these factors may affect the phenology and intensity of the season. Readiness to flower in a plant, and the amount of pollen produced, is the result of conditions during an often long period foregoing flowering. When a plant is ready to flower, temporary ambient circumstances e.g., irradiation and humidity, determine the timing of the actual pollen release. In order to understand variation between years and to be able to safely predict future situations, not least due to the ongoing climate change, it is necessary to know the determinants of all related processes and differences between and within species, here reviewed.

Stimulation of soil microbial activity by essential oils

Summary. Although essential oils are well known antimicrobial agents, some microorganisms are activated by them and can use them as a carbon and energy source; this is the case for soil bacteria from Mediterranean ecosystems. We examined the assumption that soil microorganisms when offered with an essential oil, to which they had been previously exposed, would respond faster making immediate use of the newly added substrate. Origanum vulgare subsp. hirtum, Rosmarinus officinalis, Mentha spicata, and Coridothymus capitatus plants were collected and their essential oils isolated. Soil samples from the upper surface layer, beneath these aromatic plants, were also collected. All possible combinations of essential oils and soil samples were examined as well as the effect of the oil of R. officinalis and the non-indigenous, Lavandula angustifolia, on soil samples collected from cultivated fields. Soil respiration was used as a measure of the microbial activity. Oils (0.1 ml) were repeatedly added to the soil samples (150 g) and CO2 release was measured every seven days. Essential oils differed in their chemical composition. In spite of that, they activated respiration of the different soil samples, even of those not previously exposed to essential oils, to a comparable degree. These results suggest that essential oils are used as a carbon and energy source by rather ubiquitously occurring soil microorganisms and provide evidence that they would not accumulate in the soil, if environmental conditions favour growth of these microorganisms.

Exploring Biodiversity in the Bacterial Community of the Mediterranean Phyllosphere and its Relationship with Airborne Bacteria

We studied the structure and diversity of the phyllosphere bacterial community of a Mediterranean ecosystem, in summer, the most stressful season in this environment. To this aim, we selected nine dominant perennial species, namely Arbutus unedo, Cistus incanus, Lavandula stoechas, Myrtus communis, Phillyrea latifolia, Pistacia lentiscus, Quercus coccifera (woody), Calamintha nepeta, and Melissa officinalis (herbaceous). We also examined the extent to which airborne bacteria resemble the epiphytic ones. Genotype composition of the leaf and airborne bacteria was analysed by using denaturing gradient gel electrophoresis profiling of a 16S rDNA gene fragment; 75 bands were cloned and sequenced corresponding to 28 taxa. Of these, two were found both in the air and the phyllosphere, eight only in the air, and the remaining 18 only in the phyllosphere. Only four taxa were found on leaves of all nine plant species. Cluster analysis showed highest similarity for the five evergreen sclerophyllous species. Aromatic plants were not grouped all together: the representatives of Lamiaceae, bearing both glandular and non-glandular trichomes, formed a separate group, whereas the aromatic and evergreen sclerophyllous M. communis was grouped with the other species of the same habit. The epiphytic communities that were the richest in bacterial taxa were those of C. nepeta and M. officinalis (Lamiaceae). Our results highlight the remarkable presence of lactic acid bacteria in the phyllosphere under the harsh conditions of the Mediterranean summer, the profound dissimilarity in the structure of bacterial communities in phyllosphere and air, and the remarkable differences of leaf microbial communities on neighbouring plants subjected to similar microbial inocula; they also point to the importance of the leaf glandular trichome in determining colonization patterns.

Structural and functional divergence of Campanula spatulata subspecies on Mt Olympos (Greece)

Abstract. Campanula spatulata is represented on Mt Olympos (2917 m) by two subspecies: the lowland spruneriana, from 400 to 1100 m, and the upland spatulata, from 1700 m to 2500 m. Spatulata populations significantly differed from those of spruneriana in the following features: (i) they consisted of shorter individuals with smaller flowers and lower flower production, (ii) they allocated more energy and resources below ground, (iii) they flowered much later in the year, had longer duration of flowering, and longer flower life span, (iv) they produced smaller fruits with fewer but heavier seeds, (v) they received lower numbers of insect visits for fewer hours per day, and (iv) they were pollinated by smaller insects. Between and within subspecies comparisons showed that in most cases the patterns of character change were neither gradual nor monotonous all along the elevation gradient. The differences in phenological characters are in agreement with patterns associated so far with elevation change. The taxonomic and biometric differences of the insect pollinators as well as the temporal separation of the flowering periods provide substantial evidence of reproductive isolation of the two C. spatulata subspecies on Mt Olympos.

Origanum onites (Lamiaceae) in Greece: Distribution, volatile oil yield, and composition

Origanum onites, widely used as a spice, grows wild in southern and southeastern Greece, especially in phryganic ecosystems. Like other woody plants of these ecosystems, it is characterized by seasonal dimorphism, an adaptation to face the summer drought. Its range in Greece is defined, and the features of its volatile oil are studied. It appears to be a fairly stable species, both from the morphological and chemical point of view. The high yields in volatile oil and high contents of carvacrol from all populations studied suggest the possibility of further profitable exploitation.