Abstract
The exudation of certain organic anions and protons by roots which may affect solubility of metals and P and uptake by plants, is affected by nitrogen form and pH. The objective of this work was to study exudation of carboxylates and H+/OH− by tomato plants in response to NH4/NO3 ratio and pH in nutrient solution. Four NH4/(NH4+NO3) ratios (R= 0, 0.33, 0.67 and 1) and constant vs. variable solution pH treatments were investigated. The sum of the exudation rates of all carboxylates tended to decline with increasing R, particularly tri- and dicarboxylates. The molar fraction of the exuded tri- and dicarboxylates, averaged over all treatments and plant ages, increased in the order tartarate ∼2%), malate (∼6%), succinate (∼15%), citrate (∼26%) and fumarate (∼46%). At R=1 the solution pH dropped from 5.2 to ∼3 and at R=0 increased to ∼8. The R corresponding to the pH stat of tomato plant was ∼0.3. For the constant solution pH treatment, the effect of solution pH on carboxylate exudation rate was small as compared to the effect of R. The exudation of citrate and H+ efflux which were initiated when NO3 and NH4 uptake rates per plant exceeded certain threshold values, increased with plant age.
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Imas, P., Bar-Yosef, B., Kafkafi, U. et al. Release of carboxylic anions and protons by tomato roots in response to ammonium nitrate ratio and pH in nutrient solution. Plant and Soil 191, 27–34 (1997). https://doi.org/10.1023/A:1004214814504
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DOI: https://doi.org/10.1023/A:1004214814504