Hydraulic conductivity of soil-grown lupine and maize unbranched roots and maize root-shoot junctions

Meunier, Félicien [UCL] Zarebanadkouki, Mohsen [Division of Soil Physics, University of Bayreuth, Bayreuth, Germany] Ahmed, Mutez A [Division of Soil Physics, University of Bayreuth, Bayreuth, Germany] Carminati, Andrea [Division of Soil Physics, University of Bayreuth, Bayreuth, Germany] Couvreur, Valentin [UCL] Javaux, Mathieu [UCL]

Improving or maintaining crop productivity under conditions of long term change of soil water availability and atmosphere demand for water is one the big challenges of this century. It requires a deep understanding of crop water acquisition properties, i.e. root system architecture and root hydraulic properties among other char- acteristics of the soil-plant-atmosphere continuum. A root pressure probe technique was used to measure the root hydraulic conductances of seven-week old maize and lupine plants grown in sandy soil. Unbranched root seg- ments were excised in lateral, seminal, crown and brace roots of maize, and in lateral roots of lupine. Their total hydraulic conductance was quantified under steady-state hydrostatic gradient for progressively shorter seg- ments. Furthermore, the axial conductance of proximal root regions removed at each step of root shortening was measured as well. Analytical solutions of the water flow equations in unbranched roots developed recently and relating root total conductance profiles to axial and radial conductivities were used to retrieve the root radial hydraulic conductivity profile along each root type, and quantify its uncertainty. Interestingly, the optimized root radial conductivities and measured axial conductances displayed significant differences across root types and species. However, the measured root total conductances did not differ significantly. As compared to mea- surements reported in the literature, our axial and radial conductivities concentrate in the lower range of her- baceous species hydraulic properties. In a final experiment, the hydraulic conductances of root junctions to maize stem were observed to highly depend on root type. Surprisingly maize brace root junctions were an order of magnitude more conductive than the other crown and seminal roots, suggesting potential regulation me- chanism for root water uptake location and a potential role of the maize brace roots for water uptake more important than reported in the literature.