Abstract
Fertilization of agricultural plants with ammonium [Formula: see text] is often desirable because it is less susceptible to leaching than nitrate [Formula: see text] 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 [Formula: see text] and increasing the tolerance to [Formula: see text] 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 [Formula: see text] fertilization. Although [Formula: see text] at proportions ≥25 % of total nitrogen (N) decreased leaf dry mass (DM), supplementary Ca ameliorated this decrease. Increasing [Formula: see text] resulted in decreased root hydraulic conductance (Lo) and root water content (RWC), suggesting that water uptake by roots was impaired. The [Formula: see text]-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 [Formula: see text] may be more of a reflection on its effect on the water status of the plant. Bell pepper plants that received [Formula: see text] had a low concentration of [Formula: see text] 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 [Formula: see text] 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 results suggest that it may be used as a tool to increase the tolerance to [Formula: see text] fertilization.
Highlights
Nitrate (NO3−) and ammonium (NH4+) are the predominant forms in which nitrogen (N), a critical nutrient for the growth of agricultural species (Berger et al 2013), is absorbed; the growth of cultivated plants may be affected by the predominant form of N present in the soil or nutrient solution
The objective of the present study was to determine the effect of NH4+ nutrition on growth, photosynthetic parameters, root hydraulic conductance (Lo), leaf water potential, antioxidant enzymes, nitrate reductase activity (NRA) and the nutrient status of Capsicum annuum cv
Photosynthesis, transpiration rate and stomatal conductance were unaffected by the proportion of NH4+ in the nutrient solution (Table 2)
Summary
Nitrate (NO3−) and ammonium (NH4+) are the predominant forms in which nitrogen (N), a critical nutrient for the growth of agricultural species (Berger et al 2013), is absorbed; the growth of cultivated plants may be affected by the predominant form of N present in the soil or nutrient solution. High concentration of NH4+ may be toxic to some agricultural species (Borgognone et al 2013), mainly due to a depletion of carbon supply caused by damage to the chloroplast ultrastructure (Takacs and Tecsi 1992), decreased photosynthesis rate (Setien et al 2013) and an energydemanding transmembrane NH4+ cycle in order to maintain low intracellular NH4+ concentrations (Britto et al 2001). Other plant responses to high concentration of NH4+ include increased intracellular pH (Bittsanszky et al 2015), damage to the cell membrane permeability (M’rah-Helali et al.2010) and decrease in the uptake of essential cations such as potassium (K), calcium (Ca) and magnesium (Mg)
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