Hideyuki Matsumura

Radiocesium contaminations of 20 wood species and the corresponding gamma-ray dose rates around the canopies at 5 months after the Fukushima nuclear power plant accident

Radiocesium ((134)Cs + (137)Cs) deposition from the Fukushima nuclear power plant accident was measured in 20 woody plants (12 evergreen and 8 deciduous species) grown in Abiko (approximately 200 km SSW from the NPP). Leaves (needles) and twigs were sampled from each of three foliar positions (top, middle, and bottom) in the plant canopy in early August 2011. At the time, soils around the plants were also sampled, and gamma radiation dose rates were measured at each sampling position. The average radiocesium activity in the observed leaves of the evergreen species was 7.7 times that in the leaves of the deciduous species. Among the observed evergreen coniferous species, the activity in pre-fallout-expanded leaves was 2.4 times that in the post-fallout-expanded leaves. Notably, a distinct variation in the activity among the evergreen coniferous species could be observed for the post-fallout-expanded leaves but not for the pre-fallout-expanded leaves. Although these differences depend on whether the leaves had expanded at the time of the fallout, it is probable that a considerable amount of radiocesium was translocated to newly developed leaves at a species-specific rate. In addition, it was demonstrated that dose rates around woody plants were not consistent with the prevailing prediction that general dose rates correspondingly decrease with monitoring height from the ground. Thus, the dose rates in the top foliar layer of the deciduous species decreased more than predicted, whereas those in the top foliar layer of the coniferous species did not decrease. This may be due to differences in the balance between the attenuation resulting from a shielding effect of the plant bodies and the higher radiocesium accumulation in the leaves.

Establishing critical levels of air pollutants for protecting East Asian vegetation — A challenge

Critical levels of ozone (O3) and sulfur dioxide (SO2) for protecting European forests are not evaluated to apply to East Asian vegetation. Based on the results obtained from the long-term experimental studies on the effects of chronic exposure to O3 or SO2 on 30 young potted grown tree species using open-top chambers, we analyzed dose-response relationships between the whole-plant dry mass increment during the experiment and concentration of air pollutants to establish Asian critical levels.

Impacts of Ambient Ozone and/or Acid Mist on the Growth of 14 Tree Species: An Open-Top Chamber Study Conducted in Japan

Young trees of 14 species were exposed to ambient ozone (O3), (charcoal-filtered air [CF] or non-filtered air [NF]) and/or acid mist (pH 5 or 3 : SO4 2, NO3, Cl- at equivalent 1:2:1 ratio) over three seasons (from June 1993 to November 1995) using tunnel-type open-top chambers at two sites (Abiko: 25 ma.s.l. and Akagi: 540 m a.s.l.)in Japan. Ambient, 12-hr (0600-1800) mean O3 concentration for April-September during the period of experiment at Akagi (41 ppb) was 40% higher than that at Abiko (30 ppb). The NF- and CF-chambers had 90% and 30% of ambient O3, respectively. Significant decreases in biomass in the NF treatments were observed in Pinus densiflora, Larix kaempferi, Picea abies, Abies firma, Abies homolepis, Abies veitchii, Cryptomeriajaponica, Populus maximowiczii, Betula platyphylla, Fagus crenata and Zelkova serrata as compared with the CF treatment. These results indicate that the current ambient level of O3 in Japan is high enough to have adverse effects on the growth of all tree species examined, except Pinus thunbergii, Chamaecyparis obtusa and Quercus mongolica. Increasing acidity of mist caused no growth decreases in all tree species examined However, the growth decreases by O3 were greater at pH3 mist treatment than at pH 5 mist treatment on Abies veitchii and Fagus. this suggested that the O3 effect on tree growth can be exacerbated by the deposition of acid mist, possibly associated with nitrate.

Risk assessment of ozone impact on Fagus crenata in Japan: consideration of atmospheric nitrogen deposition

Tropospheric ozone (O3) is considered to be the air pollutant relating to the decline of Fagus crenata forest in Japan. In the present study, we assessed a risk of O3 impact on the growth of F. crenata in Japan, giving consideration to the effects associated with atmospheric nitrogen (N) deposition based on the experimental study, national monitoring data for oxidant concentration and atmospheric N deposition, and a national vegetation survey. The average and maximum O3-induced relative growth reduction (RGred) of F. crenata across Japan were estimated to be 3.2 and 9.7%, respectively. Current levels of atmospheric N deposition were found to significantly affect the sensitivity of F. crenata to O3. When the N deposition was assumed as zero, the estimated average and maximum RGred were 2.3% and 5.7%, respectively. The inclusion of atmospheric N deposition data thus increased the estimated values for average and maximum RGred (by 38% and 71%, respectively). Our results demonstrate that a change in the sensitivity to O3 associated with atmospheric N deposition is an important consideration in the risk assessment of O3 impact on the growth of F. crenata in Japan.

Risk assessment of ozone impact on the carbon absorption of Japanese representative conifers.

A risk assessment of ozone (O3) impact on the annual carbon absorption (ACA) of Japanese representative conifers was conducted based on the results of an experimental study, monitoring data of oxidant concentrations and vegetation surveys. The areas with high O3-induced reduction in ACA did not necessarily correspond to the areas with relatively high O3-exposure. Widespread distribution of O3-sensitive tree species such as Pinus densiflora and Larix kaempferi, and high ACA were important factors that induced a high risk of O3 impact on the ACA. Therefore, we concluded that not only the accumulated O3-exposure but also the variety of tree habitat, the tree sensitivity to O3 and the ACA among the tree species must be taken into account to assess the risk of O3 impact on the ACA of Japanese conifers. The O3-induced reduction in the total ACA of the three tree species in Japan was estimated to be 0.8%.

Effects of Nitrogen Supply on the Sensitivity to O3 of Growth and Photosynthesis of Japanese Beech (Fagus crenata) Seedlings

To obtain basic information for evaluating critical levels of O3 under different nitrogen loads for protecting Japanese beech forests, two-year-old seedlings of Fagus crenata Blume were grown in potted andisol supplied with N as NH4NO3 solution at 0, 20 or 50 kg ha year and exposed to charcoal-filtered air or O3 at 1.0, 1.5 and 2.0 times the ambient concentration from 16 April to 22 September 2004. The O3 induced significant reductions in the wholeplant dry mass, net photosynthetic rate at 380 μmol mol CO2 (A380), carboxylation efficiency (CE) and concentrations of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and total soluble protein (TSP) in the leaves. The concentrations of Rubisco and TSP were negatively correlated with the concentration of leaf acidic amino acid, suggesting that O3 enhanced the degradation of protein such as Rubisco. The N supply to the soil did not significantly change the whole-plant dry mass and A380, whereas it significantly increased the CE and concentrations of Rubisco and total amino acid. No significant interactive effects of O3 and N supply to the soil were detected on the growth, photosynthetic parameters and concentrations of protein and amino acid in the leaves. In conclusion, N supply to the soil at ≤50 kg ha year does not significantly change the sensitivity to O3 of growth and net photosynthesis of Fagus crenata seedlings.

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.

EFFECT OF SIMULATED ACID RAIN ON THE GROWTH OF JAPANESE CONIFERS GROWN WITH OR WITHOUT FERTILIZER

Three-year old cuttings of Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa) and Sawara cypress (Chamaecyparis pisifera) were grown in pots with andosol and were exposed to simulated acid rain (SAR) at pH 2.0, 3.0, and 4.0 for 23 months. Total precipitation was 2460, 3960, or 5450 mm and SAR contained sulfuric, nitric and chloric acid at equivalent ratio of 5∶2∶3. Deionized water of pH 5.6 was a control. Exposure to SAR at pH 2.0 induced visible foliar injuries, but not any visible symptoms at pH 3.0 or higher. Total dry weights of 3 conifer cuttings grown with fertilizer were about two fold of those in plants grown without fertilizer and they reduced significantly by the exposure to SAR at pH 2.0. However, Cryptomeria japonica without fertilizer increased dry weights even though plants developed reddish-brown necrosis in large parts of tops. These 3 coniferous cuttings did not show any significant growth reduction at pH 3.0 and 4.0. Soil pH after receiving 5450 mm of SAR at pH 2.0 was 4.0 and molar ratio of (K+Ca+Mg)/Al in water and 1M ammonium acetate soluble fraction of the soil was about 0.3 and 0.4. respectively. However, dry weight of root in plants grown without fertilizer did not decrease. This suggested that growth reduction in plants fertilized and exposed to pH 2.0 was due to a reduction in photosynthetic organs associated with visible injuries, but not direct linkage with root growth inhibition due to soil acidification stress.

Effects of Simulated Acid Rain on Asian Trees

We summarized the results obtained from experimental studies on the growth and physiological responses of Japanese and Chinese tree species to simulated acid rain, mist, or fog. Based on the studies conducted in Japan and China, exposure to simulated acid rain, mist, or fog at pH 4.0 or above for one to three growing seasons did not induce any adverse effects on the growth and physiological functions of Japanese and Chinese tree species. Current acidic rain monitored in Japan and China, where the lowest acidity of ambient precipitation was around pH 4.0, was not found to induce any direct significant effects in the tree species examined.

Combined Effects of Simulated Acid Rain and Other Environmental Factors on Asian Trees

We summarized the results obtained from experimental studies on the combined effects of concurrent or sequential exposure to simulated acid rain, mist, or fog, and ozone, on the growth and physiology of Japanese and Chinese tree species. Based on the limited number of studies conducted in Japan and China, we found that the combined effects of acid precipitation and ozone on Japanese and Chinese tree species were additive or greater than additive. Moreover, there is a possibility that acid precipitation with a relatively low acidity increased the extent of ozone-induced inhibition of assimilate translocation from the shoot to roots, and this ozone effect on trees exacerbated by acid precipitation may be associated with nitrate input from precipitation.