Submitted to: Annals Of Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/30/2013
Publication Date: 9/1/2013
Citation: Locke, A.M., Sack, L., Bernacchi, C.J., Ort, D.R. 2013. Soybean leaf hydraulic conductance does not acclimate to growth at elevated [CO2] or temperature in growth chambers or in the field. Annals Of Botany. 112(5):911-918. Interpretive Summary: For each molecule of CO2 that a leaf acquires from the atmosphere it sacrifices 500 to 1000 molecules of water. Plants have numerous mechanisms to keep this lopsided ratio as reasonable as possible and collective these mechanisms define the water use of efficiency of the plant. Plants have the capacity to adapt to conditions of drought and high temperature in order to sustain the highest water use efficiency possible but the mechanism of these adaptation is not known. It was discovered in this study that the water transport pathway in leaves plays only a minor role in the adaptation of leaf water use efficiency to drought, elevated CO2 and elevated temperature.
Technical Abstract: Leaf hydraulic properties are strongly linked with transpiration and photosynthesis in many species. However, it is not known if gas exchange and hydraulics will have coordinated responses to climate change. Our objective was to investigate the responses of leaf hydraulic conductance (Kleaf) in Glycine max(soybean) to elevated[CO2] and increased temperature compared with the responses of leaf gas exchange and leaf water status. Two controlled environment growth chamber experiments were conducted with soybean to measure Kleaf, stomatal conductance (gs), and photosynthesis (A) during growth at elevated [CO2] and temperature relative to ambient levels. These results were validated with field experiments on soybean grown under free-air elevated [CO2] and canopy warming. In chamber studies, Kleaf did not acclimate to growth at elevated [CO2], even though stomatal conductance decreased and photosynthesis increased. Growth at elevated temperature also did not affect Kleaf, although gs and A showed significant but inconsistent decreases. The lack of response of Kleaf to increased [CO2] and temperature in chamber-grown plants was confirmed with field-grown soybean. Leaf hydraulic and leaf gas exchange responses to these two climate change factors were not strongly linked in soybean, although stomatal conductance responded to [CO2] and increased temperature as previously reported. This differential behavior could lead to an imbalance between hydraulic supply and transpiration demand under extreme environmental conditions likely to become more common as global climate continues to change. However, the maintenance of Kleaf despite reduction of gs would contribute to a high hydraulic supply capacity relative to demand, which could provide a mechanism for soybean under higher [CO2] and temperature to better maintain open stomata during the onset of mild to moderate soil drying.