Triple super phosphate impact on maize root hydraulic conductance

The discovery that application of triple super phosphate (TSP) to near-neutral pH soils induced plant drought resilience opened the possibility of a new approach to managing crops for water-deficit conditions. A key component of the TSP response appeared to be decreased root hydraulic conductance. In the current study, maize plants were grown on hydroponic solutions to investigate characteristics of root hydraulic conductance response to TSP.

Maize (Zea mays L.) was grown on hydroponic solutions to which responses to pH, TSP and H2PO4- concentrations, and timing of changes in solution pH were determined. Root hydraulic conductance was determined for seedlings by placing them in a pressure chamber and measuring sap exudation for 1 h with the root system subjected to 0.2 MPa atmospheric pressure.

Root hydraulic conductance decreased to approximately 40 % of the value for TSP-grown plants at solution pH 6.75 as compared to plants grown with diammonium phosphate. Also, hydraulic conductance decreased when solution concentrations of TSP and of H2PO4- were increased. A test of the temporal response to solution pH change showed root hydraulic conductance altered from the unchanged pH value required at least 2-4 d, indicating longer-term response to pH treatment than purely a biochemical response.

These results quantified specific conditions under which TSP caused decreases in root hydraulic conductance in the studied maize hybrid. Decreased root hydraulic conductance observed in response to TSP and near-neutral pH was congruent with previous observations of TSP-induced decreases in soil water extraction at elevated soil water content, which has been identified as a basis for crop drought resilience.