Effects of Ozone and/or Excess Soil Nitrogen on Growth, Needle Gas Exchange Rates and Rubisco Contents of Pinus Densiflora Seedlings |
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| Authors: | Tatsuro Nakaji Takeshi Izuta |
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| Institution: | 1. United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo, 183-8509, Japan
2. Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo, 183-8509, Japan
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| Abstract: | The effects of ozone (O3) and excess soil nitrogen (N), singly and in combination, on growth, needle gas exchange rates and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) contents of Pinus densiflora seedlings were investigated. One-year-old seedlings were grown in 1.5-L pots filled with brown forest soil with 3 levels of N supply (0, 100 or 300 mg N·L?1 fresh soil volume). The seedlings were exposed to charcoal-filtered air or 60±5 nL·L?1 O3 (8 hours a day) in naturally-lit phytotrons for 173 days from 22 May to 11 November. The exposure to O3 or high N supply to the soil caused a significant reduction in the dry weights of the seedlings. Although no significant interactive effects of O3 and excess soil N were detected on the dry weight growth of the seedlings, the whole-plant dry weight of the O3-exposed seedlings grown in the soil treated with 300 mg N·L?1 was greatly reduced compared with the control value. Ozone reduced net photosynthetic rate at 350 µmol·mol?1 CO2 (A 350 ), carboxylation efficiency (CE) of photosynthesis and Rubisco content without a significant change in the gaseous phase diffusive conductance to CO2 (gs) of the needles. The excess soil N reduced the A 350 , CE, gs and Rubisco content of the needles. These results suggest that the reduction in the dry weight growth of Pinus densiflora seedlings induced by the exposure to O3 and/or excess soil N was caused by reduction in the net photosynthetic rate mainly due to the decrease of Rubisco quantity in the chloroplasts. |
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