Supplementary calcium ameliorates ammonium toxicity by improving water status in agriculturally important species

• Published in: AoB plants 2015-09, Vol.7, p.plv105
• Main Authors: Hernández-Gómez, Elvia, Valdez-Aguilar, Luis A., Cartmill, Donita L., Cartmill, Andrew D., Alia-Tajacal, Irán
• Format: Article
• Language: English
• Subjects: Calcium; Electrolytes; Lipid peroxidation; Nitrates
• ISSN: 2041-2851; 2041-2851
• DOI: 10.1093/aobpla/plv105

Fertilization of plants with ammonium is highly desirable because it is less susceptible to leaching than nitrate, with associated reductions in environmental pollution and risk to human health; however, important agricultural species exhibit a reduction in growth when fertilized with high levels of ammonium. The present study proved that tolerance to ammonium can be increased in bell pepper plants when calcium is incorporated at higher concentrations; calcium should thus be integrated into crop management to enhance the tolerance of agricultural plants to excess ammonium. Abstract Fertilization of agricultural plants with ammonium (NH4+) is often desirable because it is less susceptible to leaching than nitrate (NO3−), reducing environmental pollution, risk to human health and economic loss. However, a number of important agricultural species exhibit a reduction in growth when fertilized with NH4+, and increasing the tolerance to NH4+ may be of importance for the establishment of sustainable agricultural systems. The present study explored the feasibility of using calcium (Ca) to increase the tolerance of bell pepper (Capsicum annuum) to NH4+ fertilization. Although NH4+ at proportions ≥25 % of total nitrogen (N) decreased leaf dry mass (DM), supplementary Ca ameliorated this decrease. Increasing NH4+ resulted in decreased root hydraulic conductance (Lo) and root water content (RWC), suggesting that water uptake by roots was impaired. The NH4+-induced reductions in Lo and RWC were mitigated by supplementary Ca. Ammonium induced increased damage to the cell membranes through lipid peroxidation, causing increased electrolyte leakage; Ca did not reduce lipid peroxidation and resulted in increased electrolyte leakage, suggesting that the beneficial effects of Ca on the tolerance to NH4+ may be more of a reflection on its effect on the water status of the plant. Bell pepper plants that received NO3−N had a low concentration of NH4+ in the roots but a high concentration in the leaves, probably due to the high nitrate reductase activity observed. Ammonium nutrition depressed the uptake of potassium, Ca and magnesium, while increasing that of phosphorus. The results obtained in the present study indicate that NH4+ caused growth reduction, nutrient imbalance, membrane integrity impairment, increased activity of antioxidant enzymes and affected water relations. Supplementary Ca partially restored growth of leaves by improving root Lo and water relations, and our re