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Absorption Rates of Ammonium and Nitrate by Red Kidney Beans under Salt and Water Stress¹

ABSTRACT

The purpose of this study was to gain additional knowledge regarding the influence of salinity and water deficit on plant uptake of NH₄⁺ and NO₃^-. The absorption patterns of NH₄⁺ and NO₃^- by red kidney beans (Phaseolus vulgaris L.) were determined under normal conditions (control), NaCl treatment (salt stress), and carbowax treatment (water stress) using an inverse isotope dilution technique with ¹⁵N. Salt and water stress inhibited the absorption of both NH₄⁺ and NO₃^-. There was no difference between these two stress treatments in NH₄⁺ uptake, but carbowax restricted NO₃^- uptake more than did NaCl. Under NaCl salinity the plants absorbed the same amount of N independent of N source; under water stress more NH₄⁺ than NO₃^- was absorbed. Water absorption was reduced by both stress treatments; N and water uptake were highly correlated. Root permeability decreased in plants subjected to stress. Dry matter production and total N per plant decreased, but the N percentage increased in the stressed plants.

¹ Contribution from the Dep. of Soils, Water & Engineering, Arizona Agric. Exp. Stn., Tucson, AZ 85721. Published with approval of the Director as Journal Article no. 2812.

² Former Graduate Student and Professor, respectively, Dep. of Soils, Water & Engineering, Univ. of Arizona. The senior author is now located at Fortaleza, Ceara, Brazil.

Received for publication January 13, 1978. Accepted for publication May 16, 1978.