For most plant species, elevated atmospheric CO2 levels lead to a decrease in stomatal conductance (gs) by causing the partial closure of the stomata. This allows the plant to decrease transpirational water loss. Current knowledge of the molecular-level control of stomatal CO2 response is based primarily on studies that investigated response to short-term CO2 changes, on the scale of minutes to hours. It’s unclear, however, whether this data is representative of longer-term changes occurring over weeks or months. With atmospheric CO2 levels projected to double over the next century, long-term stomatal response could have a major impact on plant water use in the future, and an understanding of its regulation could help researchers to improve crop water-use efficiency.
In a new study published in Annals of Botany, lead author Karin S.L. Johansson and colleagues studied the genetic controls of short- and long-term gs responses to elevated CO2 levels. The researchers used two arabidopsis recombinant inbred lines, one with a strong CO2 response, and one with a weak CO2 response, and employed quantitative trait locus (QTL) mapping to pinpoint loci controlling gs responses.
The authors found that short- and long-term stomatal responses were both associated with a QTL on chromosome 2 that explained about half of the short-term variation seen in responses between the weak and strong lines. Elevated CO2 caused an average gs decrease of 26% in the arabidopsis lines tested, which is similar to what has been found in field experiments studying long-term response. The plants also showed a 60% increase in total leaf area.
“The fact that short- and long-term CO2 responses were significantly correlated and associated with the same locus suggests that knowledge about the signalling pathway for short-term gs regulation in response to elevated CO2 concentration could be used for manipulation of long-term gs responses under rising atmospheric CO2,” write the authors. They note that breeding crops for high water-use efficiency could produce varieties able to grow in arid regions, as has already been accomplished with wheat. “Large differences in gs or water-use efficiency observed among cultivars of wheat, rice, maize, legumes, cotton, and sugarcane show that there is a large untapped potential in the genetic variation for stomatal traits in crop species as well.”