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

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.