Tatsuro Nakaji

Seasonal changes in the relationship between photochemical reflectance index and photosynthetic light use efficiency of Japanese larch needles

We investigated seasonal changes in the photochemical reflectance index (PRI) and its relation to the diurnal profile of photosynthetic light use efficiency (LUE) in mature Japanese larch (Larix kaempferi Sarg.) forest throughout the growing season from June to October 2003. The daily mean value of needle PRI showed seasonal variation, strongly correlated with the chlorophyll concentration and carotenoid/chlorophyll ratio of the needles. During the green period from early June to late September, the hourly values of both PRI and LUE showed significant midday depression, and were positively correlated. In late October, however, because the PRI of yellowing needles tended to increase slightly at midday in contrast to the LUE, this correlation became negative. Even before autumn senescence, the sensitivity of PRI to LUE changed with the season. Correlation analysis indicated that the slope and intercept of the regression line of the PRI–LUE relationship increased during summer, with peaks in July and August, respectively. The seasonal change in slope was strongly correlated with the foliar photosynthetic pigment concentration, nitrogen concentration, air temperature and the daily mean value of the normalized difference vegetation index (NDVI). The value of the intercept was positively correlated with the daily mean PRI. These results suggest that although diurnal change in LUE cannot be estimated quantitatively from PRI on its own throughout the growing season, the combined use of PRI and other variables such as foliar pigments or NDVI could improve the remote evaluation of seasonal changes in LUE of deciduous tree leaves.

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 photosynthesis and leaf nutrient status of Fagus crenata seedlings grown in brown forest soil acidified with H2SO4 or HNO3 solution

To obtain basic information for evaluating critical loads of acid deposition for protecting Japanese beech forests, growth, net photosynthesis and leaf nutrient status of Fagus crenata seedlings grown for two growing seasons in brown forest soil acidified with H2SO4 or HNO3 solution were investigated. The whole-plant dry mass of the seedlings grown in the soil acidified by the addition of H2SO4 or HNO3 solution was significantly less than that of the seedlings grown in the control soil not supplemented with H+ as H2SO4 or HNO3 solution. However, the degrees of reduction in the whole-plant dry mass and net photosynthetic rate of the seedlings grown in the soil acidified by the addition of H+ as H2SO4 solution at 100xa0mgxa0l−1 on the basis of air-dried soil volume (S-100 treatment) were greater than those of the seedlings grown in the soil acidified by the addition of H+ as HNO3 solution at 100xa0mgxa0l−1 (N-100 treatment). The concentrations of Al and Mn in the leaves of the seedlings grown in the S-100 treatment were significantly higher than those in the N-100 treatment. A positive correlation was obtained between the molar ratio of (Ca+Mg+K)/(Al+Mn) in the soil solution and the relative whole-plant dry mass of the seedlings grown in the acidified soils to that of the seedlings grown in the control soil. Based on the results, we concluded that the negative effects of soil acidification due to sulfate deposition are greater than those of soil acidification due to nitrate deposition on growth, net photosynthesis and leaf nutrient status of F. crenata, and that the molar ratio of (Ca+Mg+K)/(Al+Mn) in soil solution is a suitable soil parameter for evaluating critical loads of acid deposition in efforts to protect F. crenata forests in Japan.