UPTAKE OF AMMONIUM-NITROGEN BY BLUEBERRY PLANTS

Blueberry plants (Vaccinium ashei Reade cv. Tifblue) and Citrus natsud aidai Hayata were compared in terms of their ability to regulate the u ptake of ammonium-nitrogen (NH4-N). Plants of both species were grown in N-free nutrient solutions for three days and then transferred to nu trient solutions that contained various concentrations of NH4-N. Blueb erry plants showed increases in rates of uptake of NH4-N 8 to 24 h aft er application of NH4-N. At concentrations of NH4-N above 200 muM, upt ake rates decreased to the initial value 24 h after application of NH4 -N and then increased. By contrast, seedlings of Citrus natsudaidai sh owed constant rates of uptake of NH4-N during the experiment. These re sults indicate that blueberry plants are able to repress the uptake of NH4-N periodically when they are exposed to high concentrations of ex ternal NH4-N, but not seedlings of Citrus natsudaidai.