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

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 C3 perennial, Larrea tridentata, and a C3 annual, Helianthus annuus. The plants were grown in a glasshouse under ambient (360 μmol mol–1) and elevated (700 μmol mol–1) CO2. The Lp through intact root systems was measured using a hydrostatic pressure‐induced flow system. Leaf gas exchange was also determined for both species and leaf water potential (ψleaf) was determined in L. tridentata. The Lp of L. tridentata roots was unchanged by an elevated CO2 growth environment. Stomatal conductance (gs) and transpiration (E) decreased and photosynthetic rate (Anet) and Ψleaf increased in L. tridentata. There were no changes in biomass, leaf area, stem diameter or root : shoot (R : S) ratio for L. tridentata. In H. annuus, elevated CO2 induced a nearly two‐fold decrease in root Lp. There was no effect of growth under elevated CO2 on Anet, gs, 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 in root Lp in H. annuus under elevated CO2 are currently under investigation and may relate to either axial or radial components of root Lp.