Masahiro Yamaguchi

Growth and photosynthetic responses of Fagus crenata seedlings to O3 under different nitrogen loads

To obtain the basic data for evaluating the critical level of ozone (O3) to protect Japanese deciduous broad-leaved forest tree species, the growth and photosynthetic responses of Fagus crenata seedlings to O3 under different nitrogen (N) loads were investigated. The seedlings were grown in potted andisol supplied with N as NH4NO3 solution at 0, 20 or 50xa0kgxa0ha−1 year−1 and were exposed to charcoal-filtered air or O3 at 1.0, 1.5 and 2.0 times the ambient concentration for two growing seasons. The interactive effect of O3 and N load on the whole-plant dry mass of the seedlings at the end of the second growing season was significant. The O3-induced reduction in the whole-plant dry mass of the seedlings was greater in the relatively high N treatment than that in the low N treatment. This interactive effect was mainly due to the difference in the degree of O3-induced reduction in net photosynthesis among the N treatments. The degree of O3-induced reduction in N availability to photosynthesis was greater in the relatively high N treatment than that in the low N treatment. In conclusion, the sensitivity of growth and photosynthetic parameters of F. crenata seedlings to O3 become high with increasing amounts of N added to the soil. Therefore, N deposition from the atmosphere should be taken into account to evaluate the critical level of O3 to protect Japanese deciduous broad-leaved forest tree species.

Effects of ozone on growth, yield and leaf gas exchange rates of four Bangladeshi cultivars of rice (Oryza sativa L.)

To assess the effects of tropospheric O3 on rice cultivated in Bangladesh, four Bangladeshi cultivars (BR11, BR14, BR28 and BR29) of rice (Oryza sativa L.) were exposed daily to charcoal-filtered air or O3 at 60 and 100 nl l(-1) (10:00-17:00) from 1 July to 28 November 2008. The whole-plant dry mass and grain yield per plant of the four cultivars were significantly reduced by the exposure to O3. The exposure to O3 significantly reduced net photosynthetic rate of the 12th and flag leaves of the four cultivars. The sensitivity to O3 of growth, yield and leaf gas exchange rates was not significantly different among the four cultivars. The present study suggests that the sensitivity to O3 of yield of the four Bangladeshi rice cultivars is greater than that of American rice cultivars and is similar to that of Japanese rice cultivars and that O3 may detrimentally affect rice production in Bangladesh.

Effects of ozone on growth, yield and leaf gas exchange rates of two Bangladeshi cultivars of wheat (Triticum aestivum L.)

To clarify the effects of O(3) on crop plants cultivated in Bangladesh, two Bangladeshi wheat cultivars (Sufi and Bijoy) were grown in plastic boxes filled with Andisol and exposed daily to charcoal-filtered air or O(3) at 60 and 100 nl l(-1) (10:00-17:00) from 13 March to 4 June 2008. The whole-plant dry mass and grain yield per plant of the two cultivars at the final harvest were significantly reduced by the exposure to O(3). Although there was no significant effect of O(3) on stomatal diffusive conductance to H(2)O of flag leaf, net photosynthetic rate of the leaf was significantly reduced by the exposure to O(3.) The sensitivity of growth, yield, yield components and leaf gas exchange rates to O(3) was not significantly different between the two cultivars. The results obtained in the present study suggest that ambient levels of O(3) may detrimentally affect wheat production in Bangladesh.

Influences of nitrogen load on the growth and photosynthetic responses of Quercus serrata seedlings to O3

The objectives of this study were to clarify the influences of nitrogen (N) load on the growth and photosynthetic responses of Quercus serrata seedlings to O3 and to obtain basic data for evaluating the critical levels of O3 for protecting Q. serrata forests in Japan. The effects of O3 and/or N load on growth and photosynthetic activity of Q. serrata seedlings were investigated during the two growing seasons. Two-year-old seedlings were assigned to 12 experimental treatments, which were comprised of the combination of four gas treatments (charcoal-filtered air and three levels of O3 at 1.0, 1.5 and 2.0 times ambient concentration) and three N treatments (0, 20 and 50xa0kgxa0ha−1xa0year−1). During the second growing season, no significant interactive effects of O3 and N load on the growth and net photosynthetic rate of the seedlings were detected. Threrfore, we concluded that N supply to the soil at ≤50xa0kgxa0ha−1xa0year−1 does not significantly influence the growth and photosynthetic responses of Q. serrata seedlings to O3. Based on the O3 exposure-response relationships for the whole-plant growth of the seedlings, the critical level of O3 for Q. serrata was estimated to be approximately 36xa0nmolxa0mol−1 as the average 15-h O3 concentration during the one growing season.

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%.

Evaluation of the effects of ozone on yield of Japanese rice (Oryza sativa L.) based on stomatal ozone uptake.

To evaluate the negative impact of ozone (O3) on Japanese crop plant yield based on cumulative stomatal O3 flux, a Japanese rice cultivar, Koshihikari, was exposed to O3 in O3-exposure chambers. Stomatal diffusive conductance to water vapour were measured during the experimental period. We parameterized and improved a stomatal diffusive conductance model by considering seasonal changes in stomatal diffusive conductance, as well as the acute effects of O3 on this variable. Our adjusted model accounted for 64% of the variation within the data set. Based on the results of linear regression analyses of the relationship between relative yield and cumulative O3 uptake, the negative impact of O3 on the yield of Koshihikari can be evaluated using cumulative O3 uptake with a threshold of 10xa0nmolxa0O3xa0m(-2) projected leafxa0areaxa0s(-1) and an integration period ofxa0-300 to 100xa0°C days from anthesis.

Effects of ozone on nitrogen metabolism in the leaves of Fagus crenata seedlings under different soil nitrogen loads

To clarify the effects of ozone (O3) on nitrogen (N) metabolism in the leaves of Fagus crenata seedlings under different N loads, the combined effects of O3 and N load on N enzyme activity, amino acid profiles and soluble protein concentrations were investigated. The seedlings were grown in potted andisol supplied with N at 0 (N0), 20 (N20) and 50xa0kgxa0ha−1xa0year−1 (N50) and were exposed to charcoal-filtered air or O3 at 1.0, 1.5 and 2.0 times the ambient concentration in open-top chambers from April 2004 to October 2005. The average 24-h concentrations of O3 during the two growing seasons were 11.8, 42.7, 63.3 and 83.7xa0ppb, respectively. In July 2005, exposure to O3 did not significantly affect the concentration of total free amino acids and activities of nitrite reductase and glutamine synthetase in any N treatment. Exposure to O3 significantly increased the relative content of acidic amino acids in all N treatments while it significantly reduced concentration of total soluble protein (TSP) and ratio of TSP concentration to leaf N concentration in the N50 treatment, but not in the N0 and N20 treatments. Based on the results obtained in the present study, we concluded that exposure to O3 reduces the allocation of N to soluble protein in addition to O3-induced degradation of protein in the leaves of seedlings grown under a relatively high N load, with the result that the degree of O3-induced reduction in the soluble protein was greater under a relatively high N load than under a relatively low N load.

Modeling stomatal conductance and ozone uptake of Fagus crenata grown under different nitrogen loads

A multiplicative stomatal conductance model was constructed to estimate stomatal O3 uptake of Fagus crenata exposed to O3 under different N loads to the soil. Our stomatal conductance model included environmental functions such as the stomatal responses of F.xa0crenata to diurnal changes, chronic O3 stress (AOT0), acute O3 stress (O3 concentration), and nitrogen load to soil. The model could explain 62% of the variability in stomatal conductance. We suggest therefore that stomatal closure induced by O3 and N load-induced soil acidification must be taken into account in developing a stomatal conductance model for estimating stomatal O3 uptake for future risk assessment of O3 impact on Japanese forest tree species such as F.xa0crenata.

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.