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 18d growth period, a 3d pretreatment period and during flux measurements. Plants grew best in media containing 100 mmol m−3 NH4+ and 200mmolm−3 K+ (N100/K200), followed by N2/K200 < N100/K2 < N2/K2. 86Rb+(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+]0 present during flux determinations. NH4+ was least inhibitory to 86Rb+(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.