Photosynthetic dark reaction is more sensitive to ABA signalling caused by osmotic stress than Ca2+ signalling in ginger leaves

• Photosynthetic dark reaction is less sensitive to Ca2+ signalling than ABA.
• ABA causes the active down regulation of the photosynthetic dark reaction.
• A stronger photosynthetic dark reaction results in the reopening of stomata.
• Ca2+ signalling plays an irreplaceable role in regulating stomatal conductance.

The effects of calcium deficiency on the stomatal conductance (Gs), net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), and carboxylation efficiency (CE) of ginger leaves under well-watered conditions and osmotic stress were investigated. On the third treatment day, Ca deficiency significantly decreased Gs, Pn, and Ci, while these three parameters recovered on the next day. The Ca-deficiency treatment had no significant effect on the carboxylation efficiency but the osmotic stress significantly reduced carboxylation efficiency during the experiment. The osmotic stress also significantly increased the ABA content in the ginger leaves, however, the Ca-deficiency had no significant effect on the ABA content. The above results indicate that the photosynthetic dark reaction is more sensitive to the increase of abscisic acid (ABA) caused by osmotic stress than to Ca2+ signalling. The lower intercellular CO2 concentration caused by the increased carboxylation efficiency resulted in the re-opening of stomata under Ca-deficiency treatment under well-watered conditions, while the lower carboxylation efficiency caused by increased ABA content after osmotic stress resulted in complete stomatal closure under Ca-deficiency treatment.