A comparative study of ammonium toxicity at different constatn pH of the nutrient solution

Abstract

Seedlings of 14 species were grown for 14-28 days on nutrient solution with 6 mmol.1-1 NH4 as the sole nitrogen source. Solutions acidity was were kept constant at pH 4.0, 5.0, 6.0 and 7.0 by continuous titration with diluted KOH. The following species were used: barley, maize, oats sorghum, yellow and white lupin, pea, soybean, carrot, flax, castor-oil, spinach, sugarbeet and sunflower. Most plant species grew optimally at pH 6.0 with slight reductions at pH 5.0. Growth of many species was severely inhibited at pH 4.0, but this inhibition was not observed with the legume and cereal species. Yield depressions at pH 4.0 relative to pH 6.0 were well correlated with the respective relative decreases of the K concentration in their roots (P < 0.002). In the roots of two species (sunflower and flax) total N concentrations were also strongly reduced at pH 4.0. Apparently, the interactions between uptake of K, NH4 and H ions become the prevalent problem at suboptimal pH. At pH 7.0, yields were also considerably decreased, with the exception of the lupines. At this pH, the roots of the growth inhibited plants were characterized by increased levels of total N and free NH4. It is thought that the binding capacity of the roots for NH4 is an important factor in preventing NH4/NH 3 toxicity at supraoptimal pH.

The differing responses of two Arabidopsis ecotypes to ammonium are modulated by the photoperiod regime

“…level and the buffering external pH are efficient methods to alleviate NH 4 ? toxicity and to increase growth, which were also proved in several crops (Findenegg 1987;Roosta and Schjoerring 2008;Balkos et al 2010). Particularly, the co-provision of nitrate and the elevated K ?…”

Growth Responses to N Forms in Rabbiteye and Highbush Blueberries.

“…This suggests that highbush blueberries assimilated NH4+ more efficiently but were more sensitive to accumulated free NH4+ in leaves than were rabbiteye blueberries. The sensitivity to free NH4+ is assumed to be different among species (4).…”

Influence of nitrate—ammonium ratio on growth and nutrition of Arabidopsis thaliana

“…This inhibition is correlated with concomitant decrease in root K + content (Findenegg 1987), suggesting NH 4 + -K + competition for root transporters at low pH. When medium acidification is prevented by using buffered medium, NH 4 + toxicity is generally attenuated (Maynard and Barker 1969;Claussen and Lenz 1995) and NH 4 + specific deleterious effects are revealed.…”