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Influence of ambient acidity on the absorption of nitrate and ammonium by tomato plants
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The effects of ambient acidity on nitrate and ammonium absorption by 26-day-old tomato plants (Lycopersicon esculentum Mill.) were examined in solution culture. The absorption rate per unit root mass was measured for 6 hr. The nitrate absorption rate from 0.4 mM NaNO3 was 36% greater at pH 4.5 than at pH 6.5. In contrast, the ammonium absorption rate was approximately 42% greater at pH 5.5 or 6.5. than at pH 4.5. The presence of equimolar ammonium from 0.4 mM NH4NO3 decreased the nitrate absorption rate at pH 5.5 or 6.5 but did not reduce the rate at pH 4.5. The nitrate absorption rate was inhibited less at pH 5.5 when equimolar ammonium was supplied from 0.2 mM (NH4)2SO4 as opposed to NH4NO3. At pH 5.5, the nitrate absorption rate increased with increased (NH4)2SO4 concentration. The presence of equimolar nitrate supplied as either NaNO3 or NH4NO3 had no effect on the ammonium absorption rate at pH 5.5 or 6.5. However, at pH 4.5, the ammonium absorption rate was solightly reduced from NH4NO3 solutions relative to that from a (NH4)2SO4 solution. [AS]
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 Record created 2017-10-01, last modified 2019-02-22

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