Seite - 58 - in Biodiversity and Health in the Face of Climate Change

58 3.6 Climate Change Effects Airborne pollen measurements are among the longest term datasets of biological origin, therefore representing a valuable proxy of ongoing climate change. Extensive research over the last decade has shown that airborne pollen has increased in abun- dance but pollen seasons have also shifted to an earlier timeframe and may last longer (Ziello et  al. 2012). It is still not clear, though, if this is the result of increased pollen production per floral unit or per individual plant, or the consequence of land use changes, ongoing climate change, eutrophication, global warming or a combi- nation of these and many other factors. To date, some of the main causative factors for these changes have been considered air pollutants and higher air temperatures associated with global warming, or urbanisation rates and land use changes (e.g. Voltolini et  al. 2000; Sofiev et  al. 2009). In parallel with this, allergic reactions to pollen in sensitised individuals have increased in both frequency and severity over the last decades, which is in accor- dance with the above-mentioned increase in airborne pollen concentrations (Linneberg et  al. 1999). Although the reason for this synchronicity is not thoroughly understood and the cause-effect relationship not completely determined, a correla- tion between pollen abundance and pollen sensitisation has been considered to be real (e.g. Troise et  al. 1992; Ault 2004). Overall, a very large number of factors are expected (but not limited) to be influ- enced by climate change (anthropogenic or not) and together to  contribute to the exacerbated provocation of allergic symptoms in sensitised individuals. There was an extensive review by Sofiev et  al. in 2009 where the authors discuss plant-induced human allergy, from plant pollination and pollen dispersion to modelling and fore- casting of airborne pollen concentrations. The following are some of the factors thought to be most important, although the list cannot be exhaustive: • Plant growth, as influenced by the combination of air pollutants (i.e. carbon diox- ide) and elevated air temperature, because of increased plant biomass. • Pollen production, as expressed by increased pollen or flower production per inflorescence, or by a higher number of inflorescences per plant. • Onset and duration of the pollen season, as influenced by meteorological and climatic factors, per site, among sites and among years and for each pollen type. • Pollen allergenicity, as influenced by air pollutants (e.g. ozone and nitrogen dioxide) and air temperature, but, notably, in inverse correlation to pollen pro- duction per plant, after taking into account available resources as a limiting factor. • Plant microbiome (plant, leaf, inflorescence and pollen microbiome), as deter- mined by a wide variety of environmental factors, including biodiversity per se and its temporal variability. A. Damialis et  al.