NH4+ nutrition slows down plant growth in a dose-dependent manner.
Elevated CO2 enhances photosynthesis and growth without alleviating NH4+ toxicity.
High CO2 at 7.5 mM NH4+ improves Water Use Efficiency but decreases plant N status.
The up-regulation of N metabolism under 7.5 mM NH4+ is impaired at elevated CO2.
Elevated CO2 annuls the induction of TCA anaplerotic enzymes under 7.5 mM NH4+.