| Abstract: | The nitrate uptake capacity of surface roots of spring wheat(Triticum aestivum L. cv. Kulin) was investigated followingwetting of dry surface soil. Plants were grown to stem elongationstage with adequate watering at depth while the surface soilwas allowed to dry. Eight weeks after sowing, water or a 15N-nitratesolution was added to the surface soil to simulate rainfall.Root growth and nitrate uptake were measured up to 4 d afterwetting on plants with unconfined nodal root growth and on plantswith the majority of nodal roots confined within small vials.Prior to wetting, plants from both nodal treatments had seminalroots with collapsed cortices along the upper 10 cm and manyshort, viable lateral roots. Nodal roots, where present, wereonly a few cm long and unbranched. Only plants with unconfinednodal roots were able to take up nitrate within the 24 h beforeany new root growth. By 2 d after wetting there was significantgrowth of the seminal lateral roots, and rapid growth and branchingof nodal roots. From 2 d after wetting, plants with confinednodal roots also took up nitrate, presumably due to the growthof the seminal lateral roots. Hence it appears as though thenodal roots in the unconfined treatment could immediately takeup nitrate, but the seminal roots required new lateral rootgrowth to become active in nitrate uptake. The plants with confinednodal roots had a lower nitrate uptake than those with unconfinednodal roots 4 d after wetting, indicating that the seminal rootsystem was not able to compensate for lack of nodal roots. Insufficientnitrate was taken up after 4 d, by plants from either nodalroot treatment, to increase the shoot N concentration significantly. Key words: Triticum aestivum, nitrate uptake, drought, seminal roots, nodal roots |
