Abstract
Condition of epistomatal wax on the abaxial surface of the current and previous-year needles of damaged silver fir trees (<em>Abies alba</em> Mill.), both from the polluted Risnjak and "clean" Donja Dobra sites in Gorski Kotar region, both influenced by pollutants coming from Europe, during two years, three times a year, were examined with Scanning Electron Microscope. In the course of time the wax tubules on the epistomatal rims of stomata in polluted, but also in "clean" needles surface, become fused and agglomerated rapidly to various extents of morphologically different types of amorphous wax crusts, primarily compact and particulate ones. This process begins very early, especially in polluted Risnjak site, and may be interpreted as a possible result of air pollution. However, the recrystalization, or production of new tubules, also appears relatively quickly in mostly cases. Quantitative estimations indicate a very large total amount of amorphous wax crusts in the current-year needles, and a very high percentage of the same wax in previous-year needles. Amorphous wax crusts cover stomatal pores, as well as the rims, disturbing the normal gas exchange. Statistically there is a signicant tendency of increase in wax degradation in the needles of the polluted site in comparison with those of the unpolluted one, but there is an insignificant wax degradation among the needles of damaged trees within each site. These results confirmed most of the research done in our preliminary report.
Highlights
Condition of epistomatal wax on the abaxial surface of the current and previous-year needles of damaged silver fir trees (Abies alba Mill.), both from the polluted Risnjak and clean Donja Dobra sites in Gorski Kotar region, both influenced by pollutants coming from Europe, during two years, three times a year, were examined with Scanning Electron Microscope
Like in many European and American countries coniferous forests in Croatia are declining (Huttunen 1976a, b; Bernadzki 1983; Schulze et al 1989; Komlenoviæ and Rastovski 1992; Tikviæ et al 1995; etc). this phenomenon in our country is most expressed in Gorski Kotar (Baèiæ and Popoviæ 1998), the region between the continetal part and the Mediterranean area, which is strongly influenced by different pollutants coming from the Rijeka region, northern Italy and even from the north and middle part of Europe
The opinion that air pollution is the primary cause of forest decline, especially those of silver fir trees, in Croatia was first emphasized by Durbeiæ and Kerovec (1990), it was known that other factors, abiotic, biotic and anthropogenic can be implicated, too (Opalièki 1972; Spaiæ 1972; Glava 1987; 1992a, b)
Summary
Like in many European and American countries coniferous forests in Croatia are declining (Huttunen 1976a, b; Bernadzki 1983; Schulze et al 1989; Komlenoviæ and Rastovski 1992; Tikviæ et al 1995; etc). this phenomenon in our country is most expressed in Gorski Kotar (Baèiæ and Popoviæ 1998), the region between the continetal part and the Mediterranean area, which is strongly influenced by different pollutants coming from the Rijeka region, northern Italy and even from the north and middle part of Europe. This work is the continuation of our preliminary investigations of abaxial epicuticular wax surface condition on stomatal rims of silver fir needles in Risnjak (Baèiæ and Popoviæ 1998). This one research includes two different localities, polluted and clean sites, exclusively on needles of damaged trees, two years of investigations and statistical analyses of the results. Taking into account the results of our other investigations, done in this area on silver fir trees needles, too (Baèiæ et al 2003; Baèiæ et al 2004), it is possible to attribute the needle dying to the acid rain as well as to pollution, respectively. This paper has the aim to contribute to wider knowledge on the condition of epicuticular wax on stomata of damaged trees as a consequence of pollution at both localities
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