Physiological characteristics of Japanese red pine, Pinus densiflora Sieb.et Zucc., in declined forests at Mt. Gokurakuji in Hiroshima Prefecture, Japan

The decline of Japanese red pine trees (Pinus densiflora Sieb. et Zucc.) at Mt. Gokurakuji (693 m a.s.l.), 30 km west of Hiroshima city, west Japan, w as studied. The effects of air pollution and acid deposition on the physiol ogical characteristics of the trees, especially those of the needles, were investigated. Ozone concentration was not correlated with the physiological status of the needles and SO2 concentration was not high in the declined a rea. NO2 concentration correlated negatively with needle longevity while it correlated positively with ethylene emission from 1-year-old needles. Aver age needle longevity was about 2.8 years in non-declined areas; however the longevity was 1.3 years in the most polluted area. The minimal fluorescenc e at night (F-0) of 1-year-old needles decreased with increasing NO2 concen tration. The maximum stomatal conductance (gl), net photosynthesis (P-n) an d intercellular CO2 concentration (C-i) in the declined areas were lower th an in the non-declined areas (about 50%, 30% and 20% lower, respectively). The lower C-i suggested that the major part of the decrease in P-n can be e xplained by stomatal restriction. The soil pH, N content and C/N ratio show ed no significant difference between the declined and non-declined areas. T he physiological disorders of needles were due to the damage by air polluta nts, and important roles of NO2 are suggested. Lowering of P-n and the shor tening of needle longevity appear to be the main causes of the decline in p ines in the forest decline area.