Effects of Environmental Stress on the Pollen Viability of Ornamental Tree-Species in the City of Granada (South-Eastern Spain)

Atmospheric conditions, as well as pollutants, can induce changes in the viability and germinability of the pollen grain. This process frequently occurs in cities due to the high rate of air pollution that can alter the quality of pollen, affecting its biological functions. In this work, the effect of different environmental stress factors, mainly UV-B radiation and polluting gases (CO, NO2 and SO2), on the viability and maturity of the pollen of four ornamental tree-species present in the green infrastructure of Granada, namely Acer negundo, Carpinus betulus, Olea europaea and Cupressus spp. is analyzed. Differential staining techniques were used with fresh pollen collected in areas with different exposure to environmental stress to detect intact cell membranes (Trypan blue) and the state of maturity (Pyrogallol red). It was observed that the species from sectors more exposed to environmental stress registered a low viability and were affected by factors such as UV-B radiation and atmospheric pollutants. On the contrary, the pollen from tree species growing in peri-urban forests presented a higher rate of viability and less effect of pollutant factors. Differences were also observed according to the species/genus and according to the sampling area. This modification in the morphological and/or organic composition of the pollen wall may cause a loss of quality in the reproductive processes of plants, and it may be bioindicator of the process of progressive degradation that plant species can experience in urban environments under conditions of environmental stress, and prevent the impacts that can affect other species.