Effects of simulated acid rain on epicuticular wax production, morphology, chemical composition and on cuticular membrane thickness in two clones of Sitka spruce [Picea sitchensis (Bong.) Carr.]

Abstract

SUMMARY Sticklings (rooted cuttings) of two Sitka spruce [Picea sitchensis (Bong.) Carr.] clones were exposed to simulated rain of 4 pH values (5.6, 4.2, 3.4, 2.6). Rain was applied at 2 mm h−1 for 1 h, three times weekly, for 11 wk starting 1 wk prior to bud break. A range of physicochemical cuticular characteristics were investigated on current‐year needles following 2, 6, and 11 wk of exposure. Cuticular effects were initiated well above the threshold for visible injury (pH 2.6). The magnitude and direction of cuticular response differed significantly between clones. Amount of epicuticular wax recovered was not affected by the pH of the simulated rain. Wax structure was greatly modified at pH ≤ 3.4 on needles from one clone. Changes in wax structure were accompanied by changes in chemical composition, formation of amorphous deposits with increasing rain acidity coinciding with decreases in nonacosane‐diols and increases in estolides. Cuticular membrane thickness was increased significantly (P > 0.001) in one clone and decreased in the other due to simulated rain pH. Such alterations to physico‐chemical cuticular characteristics would be expected to have consequential effects on needle surface properties such as needle wettability and retention of acidic rain.

Effects of u.v.‐B radiation on epicuticular wax production and chemical composition of four Picea species

“…1), and\or the sequence of class deposition onto the needle surface would be expected to play a role in the degree of biosynthetic response, and overall sensitivity of the cuticle to u.v.-B radiation. This has been clearly shown to be the case for needle wax response to other components of the changing atmospheric environment such as acid rain (Percy & Baker, 1990), acid vapour (Bytnerowicz et al, 1997, tropospheric ozone\acid fog (Percy, Jensen & McQuattie, 1992), or general pollution climate (Turunen et al, 1997 ;Cape & Percy, 1997). Response to changes in plant growth environment such as light quantity\quality (Cape & Percy, 1993) is also known to be influenced by shoot phenology in the four species studied here.…”

“…This might be attributed to the very early development of the epicuticular wax layer in conifer needles (Fig. 1), with considerable proportions in some spruce species already present on expanding primordia before bud break (Percy & Baker, 1990), compared with many crop species that show a more even deposition of waxes during the period of leaf expansion. It might also indicate the dominant genetic influence in the pre-determination of homologue distribution within the wax classes.…”

“…Of particular concern would be the interaction of increased u.v.-B with co-occurring air pollutants such as ozone\acid fog (Percy et al, 1992), acid rain (Percy & Baker, 1990) or mixtures of drydeposited and wet-deposited pollutants (Cape & Percy, 1997) known to alter spruce needle wax chemical composition. Even subtle changes to needle physico-chemical characteristics might result in altered micro flora\pathogen interactions, needle water loss patterns, foliar uptake rates and early needle abscission.…”

The effects of dry O3, SO2 and NO2 on reconstituted epicuticular wax tubules

“…Various hypotheses for the explanation of the phenomenon may be put forward: (1) inorganic gases not covered in this study (e.g. NjO or NO) or mixtures of air pollutants might react directly with nonacosan-10-ol (Huttunen & Laine, 1981;Cape, 1983); (2) direct reactions might be accelerated in the presence of water (Percy & Baker, 1990;Turunen & Huttunen, 1991); (3) nonacosan-10-ol might be sensitive to intermediates formed in reactions of inorganic air pollutants either with plant products like diterpenoids (Elstner, Osswald & Youngman, 1985) or with airborne organic xenobiotics like polycyclic aromatic hydrocarbons (Aceves & Grimalt, 1993); (4) tubules might be destroyed or even eroded by the mechanical impact of dust or precipitation (Baker & Hunt, 1986;Gunthardt-Goerg, 1991). These hypotheses, which imply the direct action of atmospheric conditions on epicuticular crystals, have not yet been tested experimentally.…”

Comparative investigations of cuticular permeability of conifer needles from healthy and damaged trees

“…All these studies have in common that a more or less evident alteration of ,^^^ surface wax aggregates can be observed by scanning electron microscopy (Huttunen & Laine, 1983 ;Barnes, Davison & Booth, 1988;Bermadinger, Grill & Golob, 1988;Adams, Capron & Hutchinson, 1990;Percy & Baker, 1990). As a consequetice, leaf surface wettability increased as measured by the means of contact angle determination (Cape, 1983;Percy, Jensen & McQuattie, 1992).…”