Elevated CO2 decreases the photorespiratory NH3 production but does not decrease the NH3 compensation point in rice leaves

Shin Ichi Miyazawa, Kentaro Hayashi, Hirofumi Nakamura, Toshihiro Hasegawa, Mitsue Miyao

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7 Citations (Scopus)


The exchange of gaseous NH3 between the atmosphere and plants plays a pivotal role in controlling the global NH3 cycle. Photorespiration generates NH3 through oxygenation instead of carboxylation by the CO2-fixing enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The future increase in the atmospheric CO2 concentration, [CO2], is expected to reduce plant NH3 production by suppressing RuBisCO oxygenation (Vo). We measured the net leaf NH3 uptake rate (FNH3) across NH3 concentrations in the air (na) ranging from 0.2 to 1.6nmol mol-1 at three [CO2] values (190, 360 and 750 μmol mol-1) using rice plants. We analyzed leaf NH3 gas exchange using a custom-made whole-leaf chamber system, and determined the NH3 compensation point (y), a measure of potential NH3 emission, as the x-intercept of the linear relationship of FNH3 as a function of na. Our y values were lower than those reported for other plant species. y did not decrease under elevated [CO2], although leaf NH4+ content decreased with decreasing Vo at higher [CO2]. This was also the case for γ estimated from the pH and NH4+ concentration of the leaf apoplast solution (γ'). γ' of rice plants, grown at elevated [CO2] for months in a free-air CO2 enrichment facility, was also not decreased by elevated [CO2]. These results suggest that suppression of RuBisCO oxygenation by elevated [CO2] does not decrease potential leaf NH3 emission in rice plants.

Original languageEnglish
Pages (from-to)1582-1591
Number of pages10
JournalPlant and Cell Physiology
Issue number9
Publication statusPublished - 2014 Sep
Externally publishedYes


  • Ammonia
  • Elevated CO
  • NH compensation point
  • Nitrogen metabolism
  • Photorespiration

ASJC Scopus subject areas

  • Physiology
  • Plant Science
  • Cell Biology


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