title: Particulate pollutants are capable to 'degrade' epicuticular waxes and to decrease the drought tolerance of Scots pine (Pinus sylvestris L.).
abstract: Air pollution causes the amorphous appearance of epicuticular waxes in conifers, usually called wax 'degradation' or 'erosion', which is often correlated with tree damage symptoms, e.g., winter desiccation. Previous investigations concentrated on wax chemistry, with little success. Here, we address the hypothesis that both 'wax degradation' and decreasing drought tolerance of trees may result from physical factors following the deposition of salt particles onto the needles. Pine seedlings were sprayed with dry aerosols or 50 mM solutions of different salts. The needles underwent humidity changes within an environmental scanning electron microscope, causing salt expansion on the surface and into the epistomatal chambers. The development of amorphous wax appearance by deliquescent salts covering tubular wax fibrils was demonstrated. The minimum epidermal conductance of the sprayed pine seedlings increased. Aerosol deposition potentially 'degrades' waxes and decreases tree drought tolerance. These effects have not been adequately considered thus far in air pollution research.
authors.affiliation: Institute of Crop Science and Resource Conservation, INRES-PE, Plant Nutrition Group, University of Bonn, Karlrobert-Kreiten-Str. 13, D-53115 Bonn, Germany. Electronic address: j.burkhardt@uni-bonn.de.
authors.forename: Juergen
authors.initials: J
authors.lastname: Burkhardt
authors.forename: Shyam
authors.initials: S
authors.lastname: Pariyar
mesh_terms: D000222:Adaptation, Physiological; D000393:Air Pollutants / Q000633:toxicity*; D055864:Droughts; D052638:Particulate Matter / Q000633:toxicity*; D041605:Pinus sylvestris / Q000502:physiology* / Q000648:ultrastructure; D012621:Seasons; D014885:Waxes / Q000378:metabolism
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D014885:Waxes
keywords: Aerosols; DRH; Drought; Dry deposition; ESEM; Fog; Forest decline; HAS; RH; SEM; Wax degradation; deliquescence relative humidity; environmental scanning electron microscope; g(min); hydraulic activation of stomata; minimum epidermal conductance; relative humidity; scanning electron microscope