Particulate pollutants are capable to 'degrade' epicuticular waxes and to decrease the drought tolerance of Scots...

Area of Science:

• Environmental Science
• Plant Biology
• Forestry

Background:

• Air pollution is linked to epicuticular wax degradation in conifers, often correlating with tree damage like winter desiccation.
• Previous research focused on wax chemistry with limited success in explaining these effects.
• A new hypothesis suggests physical factors from salt particle deposition may be responsible.

Purpose of the Study:

• To test the hypothesis that salt particle deposition, not just chemical composition, causes epicuticular wax degradation and reduces tree drought tolerance.
• To investigate the physical mechanisms by which salt particles affect conifer needles.

Main Methods:

• Pine seedlings were exposed to dry salt aerosols and 50 mM salt solutions.
• Needles were subjected to humidity changes within an environmental scanning electron microscope (ESEM).
• Changes in wax appearance and epidermal conductance were measured.

Main Results:

• Deliquescent salts caused an amorphous wax appearance by covering tubular wax fibrils.
• Salt expansion occurred on needle surfaces and within epistomatal chambers.
• Minimum epidermal conductance of sprayed pine seedlings increased, indicating reduced drought tolerance.

Conclusions:

• Aerosol deposition of salts can physically alter epicuticular waxes, leading to 'degradation'.
• This physical alteration increases epidermal conductance, potentially decreasing tree drought tolerance.
• The physical effects of salt deposition are crucial factors in air pollution research on trees and have been underestimated.