Tetsushi Yonekura

GROWTH AND NITROGEN AVAILABILITY OF RED PINE SEEDLINGS UNDER HIGH NITROGEN LOAD AND ELEVATED OZONE

To evaluate the effect of increasing nitrogen (N) deposition and tropospheric ozone (o3) concentrations on N-saturated forest ecosystems, we investigated the response of Japanese red pine (Pinus densiflora), an N-saturation sensitive tree species, to increasing N load under elevated o3 concentrations. one-year-old seedlings of red pine were treated with three levels of N supply (0, 50 and 100 mg N L−1 fresh soil volume) under two levels of atmospheric o3 concentration (< 5 and 60 ppb) for two growing seasons. Nitrogen treatment did not stimulate dry matter production of the seedlings. Growth inhibition was observed in the highest N treatment under low o3 and in the two higher N treatments under elevated o3. Irrespective of the o3 concentration, increasing N supply negatively affected root growth and mycorrhizal development in fine roots, resulting in a reduction in P and Mg uptake from the soil. Net photosynthetic rate was significantly reduced by both the highest N treatment under low o3 and the two higher N treatments under elevated o3, together with decreased N-availability to RubiscO. Nitrogen assimilated from No3 – to amino acid in the needles was not affected by the treatments. However, needle protein concentration was reduced by the highest N-treatment under low o3 and by the two higher N-treatments under elevated o3. These results suggest that elevated o3 potentially disturbs the N-availability in the form of protein including Rubisco, and may advance the negative effects of excessive N-deposition on N-sensitive plant species in N-saturated forests.

Growth, Net Photosynthetic Rate, Nutrient Status and Secondary Xylem Anatomical Characteristics of Fagus Crenata Seedlings Grown in Brown Forest Soil Acidified with H2SO4 Solution

Dry matter production, net photosynthetic rate, leaf nutrient status and trunk anatomical characteristics of Fagus crenata seedlings grown in brown forest soil acidified by adding H2SO4 solution were investigated. The soil acidification leaded to decreased (Ca+Mg+K)/Al molar ratio in the soil solution. Dry mass per plant of the seedlings grown in the soil treated with H+ at 120 mg·L−1 was significantly reduced compared with the control value at 0 mg·L−1. When net photosynthetic rate was reduced in the seedlings grown in the soil treated with H+ at 120 mg·L−1, the carboxylation efficiency and maximum net photosynthetic rate at saturated CO2-concentration were lower than the control values. The addition of H+ to the soil at 120 mg·L−1iinduced a reduction in the concentration of Ca in the leaf. By contrast, the concentration of Al in the leaf was increased with increasing the amount of H+ added to the soil. The annual ring formed in the seedlings grown in the soil treated with H+ at 120 mg·L−1 was significantly narrower than that at 0 (control), 10, 30, 60 or 90 mg·L−1. Based on the results obtained in the present study, we conclude that Fagus crenata is relatively sensitive to a reduction in the (Ca+Mg+K)/Al molar ratio of soil solution compared with Picea abies.

Effects of Ozone on Japanese Agricultural Crops

Field surveys and experimental studies of the effects of ozone on Japanese agricultural crops have been conducted since the early 1970s. We review these research studies comprehensively, in chronological order. In the 1970s, most studies of the effects of ozone on agricultural crops, and the evaluation of ozone-induced foliar injuries, were field surveys. Since the 1980s, there has also been considerable research using various facilities, such as open-top chambers and controlled-environment growth cabinets; these studies are concerned with the response to and mechanism of ozone influence on various crops. In addition, since the last half of the 1990s, informative studies have been carried out to assess and map critical levels of ozone in relation to Japanese agricultural crops.

Effects of Ozone and/or Soil Water Stress on Growth and Photosynthesis of Fagaus Crenata Seedlings

The effects of ozone (O3) and soil water stress, singly and in combination, on the growth and photosynthesis of Fagus crenata seedlings were investigated. Four-year-old seedlings were exposed to charcoal-filtered air (<5 nmol mol-1 O3) or 60 nmol mor-1 O3, 7 hours per day (11:00)-18:00), for 156 days from 10 May to 11 October 1999 in naturally-lit growth chambers at 20/15C (6:00-18:00/18:00-6:00). During the same period, half of the seedlings in each gas treatment received 250 mL of water at the 3-day intervals (wellwatered treatment), while the rest received 175 mL of water at the 3-day intervals (water-stressed treatment). The exposure of the seedlings to O3 caused reductions in the leaf, stem, root and whole-plant dry weights. The net photosynthetic rate at 350 μmol mol-1 CO2, the maximum net photosynthetic rate at saturated CO2- concentration, carboxylation efficiency of photosynthesis and Rubisco content were significantly reduced by the exposure to O3. The soil water stress induced reductions in the stem, bud and whole-plant dry weights, transpiration rate and leaf water potential during the midday. The additive effects of O3 and soil water stress were observed on the dry matter production, leaf gas exchange rates and leaf water potential. As a result, the whole-plant dry weight of the seedlings exposed to both stresses was markedly reduced compared with that of the seedlings exposed to charcoal-filtered air and grown in the well-watered treatment.