A Review of the Response of Epicuticular Wax of Conifer Needles to Air Pollution

Abstract

The effects of air pollutants on the epicuticular wax structure of conifer needles and the ecophysiological consequences of the injuries are reviewed on the basis of published literature and the authors' recent investigations. Degradation of the epicuticular waxes, which appears as a fusion of wax tubes in the epistomatal chambers and finally results in an amorphous appearance of the waxes, is the most common micromorphological injury type observed in studies on the genera Abies, Larix, Picea, and Pinus. The rate of erosion correlates well with the level of air pollution, but clear evidence for the specificity of the symptoms for different air pollutants has not been observed. It is concluded that the erosion of the epicuticular waxes, a phenomenon with a large geographic distribution, is a relevant factor of the multiple forest decline syndrome. Erosion of the waxes can change needle wettability and rain retention. Increased needle wettability and permeability of the cuticles can result in enhanced leaching of nutrients and uptake of pollutants. Increased or decreased stomatal and cuticular diffusion resistance of the needles leads to altered transpiration rates. Due to the changed chemical microenvironment of the needles, the conifers are predisposed to various biotic and abiotic stresses. Because the epicuticular waxes are one of the first targets of a variety of air pollutants, they can widely be used as an early indicator of air pollution effects.

Ecophysiological responses of Mediterranean pines to simulated sea aerosol polluted with an anionic surfactant: prospects for biomonitoring

“…Stomatal structural damage, used as an indicator of atmospheric pollution [50], was also proved to be sensitive to surfactants. The symptomatology of stomatal damage was not specific, as it was reminiscent of that induced by other pollutants [50] and by environmental stressors of different origins [7,24].…”

“…Stomatal structural damage, used as an indicator of atmospheric pollution [50], was also proved to be sensitive to surfactants. The symptomatology of stomatal damage was not specific, as it was reminiscent of that induced by other pollutants [50] and by environmental stressors of different origins [7,24]. Several authors have attributed the alterations of epistomatal wax structures to the direct or indirect action exerted by the components of marine aerosol (salt and surfactants), either individually [28,52], or combined [10,12,20,34,35,39,43,44].…”

Seasonal changes of leaf surface contamination in beech, oak, and ginkgo in relation to leaf micromorphology and wettability

“…Holloway, 1969 b ;Rentschler, 1971). In forest decline research, many papers have been published on the interdependence between wax alteration, wettability of leaf surfaces and air pollution, and have been reviewed recently (Turunen & Huttunen, 1990 ;Huttunen, 1994). Some investigations indicate increased contamination with particles in parallel to * To whom correspondence should be addressed.…”

Diagnostics of Epistomatal Wax of Californian Pine Needles, and Their Association with Ozone-Caused Chlorotic Mottle

“…Changes in conifer needle epicuticular waxes, and especially epistomatal waxes, have been used as an early diagnostic tool in needle injuries [15] [16]. Experimental responses with different pollutants and case studies around mixed pollution sources indicate changes in epicuticular waxes especially at the top of and around the stomata.…”

“…Experimental responses with different pollutants and case studies around mixed pollution sources indicate changes in epicuticular waxes especially at the top of and around the stomata. The observations vary due to species, environment, needle ontogeny, age and longevity [15] [17] [18].…”