Response of gas exchange rates inAbies firmaseedlings to various additional stresses under chronic acid fog stress

Abstract

In order to clarify the chronic influence of acid fog on the gas exchange rates of momi fir (Abies firma Sieb. et Zucc.) trees, we exposed them to simulated acid fog (pH 3) for 3 years. The composition of the acid fog was similar to that observed in a region where momi fir trees have been declining, and it contained organic acids. We then treated the firs with various additional stresses, such as drought, low temperature, fine root cutting, ozone exposure, soil acidification, nitrogen load, and rhizosphere aluminum stress. Under chronic exposure to acid fog, the momi fir seedlings exhibited a pattern of stomatal behavior whereby they excessively opened in summer and closed in winter. Furthermore, the stomata of these seedlings tended to open during drought stress, and their needles were visibly injured after ozone exposure. The net photosynthesis rates of the seedlings exposed to acid fog were regulated by their stomatal aperture, rather than directly by acid fog. These results suggest that acid fog exposure disturbs the control of stomatal function in the momi fir seedlings. In addition, we found that chronic acid fog exposure suppressed the decrease in net photosynthesis rate, due to its nitrogen load.

Effects of chronic acid fog exposure with soil acidification or nitrogen loading on nutrient status in Abies firma seedlings

“…Soil pH (H 2 O) values after treatment are shown in a previous report (Yoshida et al 2004). A proton loading of 6 kg H ϩ /ha per year for 17 months did not cause any distinct decrease in soil pH, although we confirmed that this proton loading level could decrease the soil pH to 5.8 in the absence of seedlings.…”

“…We analyzed momi fir (Abies firma) seedlings treated with acid fog and soil acidification or nitrogen loading as shown in a previous study (Yoshida et al 2004), which gives a full description of the plant materials used, growth conditions of momi fir seedlings, and methods of acid fog exposure and proton or nitrogen loading.…”

Effects of complex stress of chronic acid fog exposure with rhizosphere aluminum on nutrient status in Abies firma seedlings

“…We found no distinct complex effect of acid fog with Al on nutrient status. Integration of the results of this study with those of the previous report, in which these stress treatments had no effect on transpiration rate or photosynthesis rate of momi fir seedlings (Yoshida et al 2004), shows that the alterations in nutrient status are not sufficiently serious to induce the decline of photosynthesis rate of momi fir seedlings. Eamus D, Fowler D (1990) Effects Acid fog n.s.…”

“…Half of the seedlings were exposed to simulated acid fog of pH 3.0 twice weekly from mid-July 1999, while the remaining seedlings were not exposed. The details on growth conditions and acid fog exposure methods are described elsewhere (Yoshida et al 2004).…”

“…In a previous study, we reported that 1 mM Al treatment with or without exposure to acid fog of pH 3 for 1 year did not alter chlorophyll concentration or gas exchange rates in momi fir seedlings (Yoshida et al 2004). These results indicated that exposure to acid fog of pH 3 and 1 mM Al seemed to be mildly stressful for momi fir seedlings.…”