HIGH TEMPORAL RESOLUTION MEASUREMENT OF NITRATE UPTAKE FROM FLOWING SOLUTIONS

The nitrate (NO3-) uptake rates of intact, 23 day old rice plants were measured to determine the relationship between the plant's NO3- nutri tion history and the NO3- uptake rate. A system for measuring NO3- upt ake was designed, built and tested. Specific design goals, which were met, include: low handling shock to the plants, high measurement accur acy (4%), high temporal resolution (10 min) and minimal mass-transfer limitations to uptake. Important design factors were identified and th e overall uncertainties in the reported measurements were computed. Th e observed uptake rates were dependent on the NO3- concentration ([NO3 -]) to which the plants were exposed for the 24 h prior to testing; pl ants pretreated at higher [NO3-] had lower uptake rates from 200 mu M NO3- solutions than plants pretreated at lower [NO3-].