Effects of high atmospheric CO2 concentration on root hydraulic conductivity of conifers depend on species identity and inorganic nitrogen source

We examined root hydraulic conductivity (Lp) responses of one-year-old seedlings of four conifers to the combined effects of elevated CO2 and inorganic nitrogen (N) sources. We found marked interspecific differences in Lp responses to high CO2 ranging from a 37% increase in P. abies to a 27% decrease in P. menziesii, but these effects depended on N source. The results indicate that CO2 effects on root water transport may be coupled to leaf area responses under nitrate (NO3−), but not ammonium (NH4+) dominated soils. To our knowledge, this is the first study that highlights the role of inorganic N source and species identity as critical factors that determine plant hydraulic responses to rising atmospheric CO2 levels. The results have important implications for understanding root biology in a changing climate and for models designed to predict feedbacks between rising atmospheric CO2, N deposition, and ecohydrology.

► Root hydraulic conductivity (Lp) in conifers is affected by increased atmospheric CO2 levels.
► This response depends on inorganic N source and species identity.
► This is the first report of Lp responses to elevated CO2 and N source in multiple species.