Growth and solute composition of the salt-tolerant kallar grass [Leptochloa fusca (L.) Kunth] as affected by nitrogen source

Abstract

A study was conducted to elucidate the effect of N form, either NH₄ ⁺ or NO₃ ⁻, on growth and solute composition of the salt-tolerant kallar grass [Leptochloa fusca (L.) Kunth] grown under 10 mM or 100 mM NaCl in hydroponics. Shoot biomass was not affected by N form, whereas NH₄ ⁺ compared to NO₃ ⁻ nutrition caused an almost 4-fold reduction in the root biomass at both salinity levels. Under NH₄ ⁺ nutrition, salinity had no effect on the biomass yield, whereas under NO₃ ⁻ nutrition, increasing salinity from 10 mM to 100 mM caused 23% and 36% reduction in the root and shoot biomass, respectively. The reduced root growth under NH₄ ⁺ nutrition was not attributable to impaired shoot to root C allocation since N form did not affect the overall root sugar concentration and the starch concentration was even higher under NH₄ ⁺ compared to NO₃ ⁻ nutrition. The low NH₄ ⁺ (≤2 mM) and generally higher amino-N concentrations in NH₄ ⁺- compared to NO₃ ⁻-fed plants indicated that the grass was able to effectively detoxify NH₄ ⁺. Salinity had no effect on Ca²⁺ and Mg²⁺ levels, whereas their concentration in shoots was lower under NH₄ ⁺ compared to NO₃ ⁻ nutrition (over 66% reduction in Ca²⁺; over 20% reduction in Mg²⁺), but without showing deficiency symptoms. Ammonium compared to NO₃ ⁻ nutrition did not inhibit K⁺ uptake, and the K⁺-Na⁺ selectivity either remained unaffected or it was higher under NH₄ ⁺ than under NO₃ ⁻ nutrition. Results suggested that while NH₄ ⁺ versus NO₃ ⁻ nutrition substantially reduced root growth, and also strongly modified anion concentrations and to a minor extent concentrations of divalent cations in shoots, it did not influence salt tolerance of kallar grass.