Transcriptional reprogramming and stimulation of leaf respiration by elevated CO₂ concentration is diminished, but not eliminated, under limiting nitrogen supply

Plant respiration responses to elevated CO₂ concentration ([CO₂]) have been studied for three decades without consensus about the mechanism of response. Positive effects of elevated [CO₂] on leaf respiration have been attributed to greater substrate supply resulting from stimulated photosynthesis. Negative effects of elevated [CO₂] on leaf respiration have been attributed to reduced demand for energy for protein turnover assumed to result from lower leaf N content. Arabidopsis thaliana was grown in ambient (370ppm) and elevated (750ppm) [CO₂] with limiting and ample N availabilities. The stimulation of leaf dark respiration was attenuated in limiting N (+12%) compared with ample N supply (+30%). This response was associated with smaller stimulation of photosynthetic CO₂ uptake, but not interactive effects of elevated CO₂ and N supply on leaf protein, amino acids or specific leaf area. Elevated [CO₂] also resulted in greater abundance of transcripts for many components of the respiratory pathway. A greater transcriptional response to elevated [CO₂] was observed in ample N supply at midday versus midnight, consistent with reports that protein synthesis is greatest during the day. Greater foliar expression of respiratory genes under elevated [CO₂] has now been observed in diverse herbaceous species, suggesting a widely conserved response.