Interactions between K+ and NH4+: Effects on ion uptake by rice roots

Interactive effects of K+ and N (principally NH4+) on plant growth and ion uptake were investigated using hydroponically grown rice (Oryza sativa L. cv, M202) seedlings by varying the availability of NH4+ or NO3- and K+ during an 18 d growth period, a 3 d pretreatment period and during flux measurements, Plants grew best in media containing 100 mmol m(-3) NH4+ and 200 mmol m(-3) K+ (N100/K200), followed by N2/K200>N100/K2>N2/K2. Rb-86(+)(K+) fluxes were increased by exposure to N during the 18 d growth period and the 3 d of pretreatment, but decreased by the presence of NH4+ during flux measurements, This inhibition was a function of prior N/K provision and the [NH4+](o) present during flux determinations. NH4+ was least inhibitory to Rb-86(+)(K+) influx in high-N/low-K plants, Pretreatments with K+ failed to stimulate NH4+ uptake, and the presence of K+ in the uptake solutions reduced NH4+ fluxes only in high-N/low-K plants.