Page - 59 - in Biodiversity and Health in the Face of Climate Change

59 • Pollution, including air, water, soil and other forms of pollution, on various spa- tial and temporal scales. • Weather events, including drought or extreme rainfall, wind gusts, thunderstorms and any kind of extreme micro- and macro-meteorological effects. • Land use changes, land management, habitat fracturing and moving to the north because of global warming. Plant phenological traits (like flowering, leaf and bud formation, fruit and pollen production) are well known to be very sensitive to environmental stress and espe- cially to temperature variability. This is particularly true for flowering and pollen production (e.g. Damialis et  al. 2011; Menzel et  al. 2006; Parmesan and Yohe 2003). There have been strong indications that plants produce more pollen, and earlier, when temperatures are higher, that is, at urban locations, lower elevations or south- ern exposure slopes, or during warmer years (e.g. Damialis et  al. 2011; Fotiou et  al. 2011). Higher rainfall prior to the inflorescence production and pollen formation and liberation also favour increased pollen and flower production (Damialis et  al. 2011). However, the implicated processes are excessively complex and influence of many other factors is involved, for example microclimatic conditions in the exam- ined site. Likewise, temperature seems to have a direct effect on allergen release, as revealed by the inter-annual variability in a study on birch pollen in Germany (Buters et  al. 2008). Air pollutants are also responsible for higher biomass production (including flower and pollen production). Wan et  al. (2002) and Wayne et  al. (2002) experi- mentally found that, especially in combination with elevated air temperature, increased carbon dioxide (CO2) did not alter pollen production per se, but increased plant biomass in Ambrosia artemisiifolia and, consequently, individual plants pro- duced more pollen. Ziska et  al. (2003) studied the same species but in real-life conditions in a gradient simulating different climatic scenarios and, likewise, found that plants exhibited higher biomass, pollen production and earlier flowering dates. Ziska et  al. (2003) additionally concluded that plant expansion rates and regional abundance may also increase with increasing CO2, thus increasing allergenic pollen exposure rates on a wider spatial scale. Air pollution and climate change do not only affect plant growth, pollen and flower production, and duration of the whole pollen season, but can also display more direct health effects by increasing the amount of allergenic proteins of the pol- len (Zhao et  al. 2016, 2017). According to Zhao et  al. (2016), elevated levels of certain pollutants, like nitrogen dioxide (NO2), which is traffic-related and hence more prevalent in urban locations, increase overall pollen allergenicity, thus also increasing the relevant allergy risk for sensitised individuals. El Kelish et  al. (2014), as well as Zhao et  al. (2017), showed that elevated pollutants change the transcrip- tome of ragweed pollen; therefore, under global change scenarios, the allergenic potential of pollen is also expected to change. Vehicular-exhaust pollution has been reported to influence the allergenicity of ragweed pollen: pollen along high-traffic 3 Climate Change and  Pollen Allergies