Plant, Cell, & Environment 22: 325-330 (1999)

Root hydraulic conductivity of Helianthus annuus and Larrea tridentata under elevated CO₂

Kim A. Huxman and Dawn S. Neuman

Department of Biological Sciences, University of Nevada, Las Vegas, Las Vegas, NV 89154-4004

*Corresponding author

Abstract

While investigations into shoot responses to elevated atmospheric CO₂ are extensive, few studies have focused on how an elevated atmospheric CO₂ environment might impact root functions such as water uptake and transport. Knowledge of functional root responses may be particularly important in ecosystems where water is limiting if predictions about global climate change are true. In this study we investigated the effect of elevated CO₂ on the root hydraulic conductivity (Lp) of a C,₃ perennial, Larrea tridentata, and a C₃ annual, Helianthus annuus. Plants were grown in a glasshouse under ambient (360 µmol mol^-1)and elevated (700 µmol mol^-1) CO₂. The L_p through intact root systems was measured using a hydrostatic pressure induced flow system. Leaf gas exchange was also determined for both species. The L_p of L. tridentata roots was unchanged by an elevated CO₂ growth environment. Stomatal conductance (g_s) and transpiration (E) decreased and photosynthetic rate (A_net) and Y_leaf increased in L. tridentata. There were no changes in biomass, leaf area, stem diameter or R:S ratio for L. tridentata. In H. annuus, elevated CO₂ induced a nearly 2-fold decrease in root L_p. There was no effect of growth under elevated CO₂ on g_s, E, above and below ground dry mass, R:S ratio, leaf area, root length or stem diameter in this species. The results demonstrate that rising atmospheric CO₂ can impact water uptake and transport in roots in a species specific manner. Possible mechanisms for the observed decrease root L_p in H. annuus under elevated CO₂ are currently under investigation and may relate to either axial or radial components of root L_p.

Keywords: hydraulic conductivity, carbon dioxide, functional root responses, water uptake, Helianthus annuus, Larrea tridentata