Fig. 4

Net carbon assimilation values (A) obtained from isotope ratio mass spectrometry (IRMS) of ¹³C labeled plant tissue are quantitatively similar to those obtained by gas exchange measurements. a Two methods to calculate A in time course labeled Arabidopsis plants adapted to different light intensities (80–500 PAR, n = 107 plants). Gas exchange measurements of cuvette enclosed plants were taken continuously during the 30–45 min pre-labeling adaptation phase, and reported values represent the average A in normal air for the 3 min prior to introducing the ¹³CO₂-containing atmosphere. For each plant, the analogous IRMS-based carbon assimilation estimate was calculated from the raw IRMS data (μg ¹³C mg⁻¹ D.W.) and converted to μmol ¹³CO₂ m⁻² s⁻¹ based on their individual leaf surface areas, rosette dry weights, and labeling times. Outliers were identified by the interquartile range rule. b The correlation between surface area and dry mass of Arabidopsis rosettes is weak and insufficient to establish a general rule used in gas exchange and ¹³C labeling experiments. Surface area was estimated by comparison to a calibrated size standard as described in methods. Mass was determined following lyophilization of the intact rosette. Each point represents a single rosette stage Arabidopsis plant 50–70 days old. Outliers were removed according to the interquartile range rule