Influence of phosphorus stress on ammonium uptake by maize

The effect of phosphorus (P) starvation on ammonium (NH4) uptake was evalua ted by growing single-cross seedlings of the male progenitor of the maize d ouble-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) wa s also tested. Ammonium uptake decreased 45.7% after two days of P stress c ompared 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 re versed when P was resupplied during the early periods of P deficiency, but this effect diminished as the P stress increased. These results suggest tha t maize plants are physiologically dependent on NH, rather than nitrate (NO 3) when under P stress.