The aim of this study was to estimate the amount of pollen produced by anemophilous woody taxa with allergenic properties and with considerable contribution in the concentration of pollen in the air of a Mediterranean city (Thessaloniki, Greece). The taxa selected are Corylus avellana, Cupressus sempervirens var. horizontalis and var. pyramidalis, Olea europaea and Platanus orientalis; each was studied in more than one sampling stations differing in elevation, direction or both. O. europaea produced the highest number of pollen grains per flower (1.3 9 10 5 ± 0.1 9 10 5 ) and P. orientalis the highest per inflorescence (3.3 9 10 6 ± 0.2 9 10 6 ). At the level of crown, pollen grains produced were of the order of 10 9 per surface/volume unit for O. europaea and the two C. sempervirens varieties; for the other two taxa, they were of the order of 10 6 . Pollen production was lower at higher elevation and northern direction and depended on the size of the floral unit sampled (flower for O. europaea, inflorescence for all other species): the bigger the floral unit, the more pollen it contained. Our results and reports from other areas, where C. sempervirens and O. europaea grow, show that these two Mediterranean species produce comparable amounts of pollen at the levels of inflorescence or flower, respectively, wherever they occur.
Parietaria judaica (Urticaceae) grows abundantly in urban areas of the Mediterranean region. Its pollen is a major allergy source. We studied the species' distribution and abundance in and around Thessaloniki (Greece), pollen production and pollen season. We also examined how urban pollution affects pollen viability. Our ultimate goal was to obtain an estimate of the species' performance and ability to expand under different environmental conditions related to climate change. We mapped P. judaica and the other Urticaceae species. In a north- and a south-facing population, we recorded the progress of P. judaica flowering and estimated the pollen content per flower, shoot and surface unit. We concurrently assessed atmospheric circulation of Urticaceae pollen. We estimated P. judaica pollen viability and Cu, Pb and Zn concentrations in plants collected from sites differing in traffic intensity. P. judaica is the most abundant Urticaceae species in the area; its occurrence has increased dramatically over the last 100 years. Production of flowers is intense in spring and autumn. Flowering started 12 days earlier in the south-facing population in spring, and 3 days later in autumn. Pollen production was higher in spring and in the south-facing population. Flower and pollen production were positively correlated with the size of the plant and the flower, respectively. Copper and lead concentrations in plants were positively correlated with pollen viability, which was higher for plants collected from high-traffic sites. P. judaica has a high phenotypic plasticity; this is a feature that promotes success of expansive and invasive species. It is also well adapted to warm and polluted urban environments. The climatic change forecast for the Mediterranean region could provoke earlier, longer, and more pronounced flowering and, consequently, more P. judaica pollen in the air. In return, this would result in increased severity of Parietaria pollinosis.
Τhe potential use of the aromatic plants Mentha spicata L. (spearmint) and Salvia fruticosa Mill. (sage) as soil amendments was evaluated. For this purpose, tomato seeds were sown in pots that had been filled with composts made from these plants and mixed with soil collected from an organically cultivated tomato field. A 2×2×4 [two types of fertilizer (synthetic and organic), two types of compost (M. spicata and S. fruticosa) and four compost rates (0%, 2%, 4% and 8%, w/w)] factorial experiment was used; the experiment was conducted twice in a growth chamber and lasted 60 days. At 0, 20, 40 and 60 days, after the establishment of the experiment, the soil bacterial and fungal abundance, the growth of nitrifying bacteria, the number of emerging weeds and the shoot length of tomato plants were measured in all treatments; at the end of the experiment, the above and belowground biomass of tomato plants was also determined. Soil microbial density increased with increasing compost rate of both species; the highest fungal and bacterial densities were recorded at 40 and 60 days, after the establishment of the experiment, respectively. Nitrifying bacteria were present in all treatments and at all sampling times. Both composts had a stimulating effect on tomato growth, which was remarkably pronounced with M. spicata. In contrast, weed emergence was reduced, but only in soils amended with M. spicata. The results suggest that M. spicata compost added at a rate of 4% to 8% is a very promising soil amendment, since it stimulates tomato growth, increases soil bacterial and fungal abundance and inhibits weed emergence. Further research is needed to elucidate the mode of action of M. spicata compost, its effect under field conditions and its possible use in mixed crop, rotational crop or cover crop systems.
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