Short- and long-term responses to elevated carbon dioxide use the same genetic controls

For most plant species, elevated atmospheric CO₂ levels lead to a decrease in stomatal conductance (g_s) 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 g_s 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 g_s 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 g_s 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 g_s regulation in response to elevated CO₂ concentration could be used for manipulation of long-term g_s 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 g_s 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.”