Throughfall chemistry and canopy interactions in a Sitka spruce plantation sprayed with six different simulated polluted mist treatments

Throughfall chemistry was studied in a mature Sitka spruce plantation in order to investigate canopy interactions, such as nitrogen absorption, cation leaching, and neutralization of rainfall passing through the canopy. The plantation had been exposed to six different simulated mist treatments including N (NH(4)NO(3)) and S (H(2)SO(4) at pH 2.5) in four replicated blocks since 1996. Throughfall and rainfall were collected from May to September 2000. The results showed that 30-35% of the applied N was retained by the canopy. There were linear relationships between the loss of H(+) and increased K(+), Mg(2+) and Ca(2+) deposition through the canopy. However these increases in K(+), Mg(2+) and Ca(2+) deposition accounted for only about 50% of total neutralization of the acidity. The relationship between the anion deficits in throughfall and the loss of H(+) implied that weak organic acid anions were involved in the neutralization of the acidity in throughfall.

Variation in CO2 assimilation rate induced by simulated dew waters with different sources of hydroxyl radical (*OH) on the needle surfaces of Japanese red pine (Pinus densifora Sieb. et Zucc.)

The hydroxyl radical (*OH) is generated in polluted dew on the needle surfaces of Japanese red pine (Pinus densiflora Sieb. et Zucc.). This free radical, which is a potent oxidant, is assumed to be a cause of ecophysiological disorders of declining trees on the urban-facing side of Mt. Gokurakuji, western Japan. Mists of *OH-generating N(III) (HNO2 and NO2-) and HOOH + Fe + oxalate solutions (50 and 100 microM, pH 5.1-5.4) simulating the dew water were applied to the foliage of pine seedlings grown in open-top chambers in the early morning. Needles treated with 100 microM N(III) tended to have a greater maximum CO2 assimilation rate (Amax), a greater stomatal conductance (g(s)) and a greater needle nitrogen content (Nneedle), suggesting that N(III) mist acts as a fertilizer rather than as a phytotoxin. On the other hand, needles treated with 100 microM HOOH + Fe + oxalate solution showed the smallest Amax, g(s), and Nneedle, suggesting that the combination of HOOH + Fe + oxalate caused a decrease in needle productivity. The effects of HOOH + Fe + oxalate mist on pine needles were very similar to the symptoms of declining trees at Mt. Gokurakuji.