Influence of phosphorus stress on ammonium uptake by maize

The effect of phosphorus (P) starvation on ammonium (NH4) uptake was evaluated by growing single-cross seedlings of the male progenitor of the maize double-cross hybrid BR 201 in nutrient solution. The kinetics of NH4 uptake were measured after P starvation and non-starvation periods of 2, 4, 6, 8, and 10 days. The effect of P addition during the study period (resupply) was also tested. Ammonium uptake decreased 45.7% after two days of P stress compared to the fully P-sufficient control. Ammonium uptake decreased 83.0% when P was withheld for 10 days. The decline in NH, uptake was partially reversed when P was resupplied during the early periods of P deficiency, but this effect diminished as the P stress increased. These results suggest that maize plants are physiologically dependent on NH, rather than nitrate (NO3) when under P stress.