Elsevier

Journal of Plant Physiology

Volume 213, June 2017, Pages 98-107
Journal of Plant Physiology

Research paper
Drought stress obliterates the preference for ammonium as an N source in the C4 plant Spartina alterniflora

https://doi.org/10.1016/j.jplph.2017.03.003Get rights and content

Abstract

The C4 grass Spartina alterniflora is known for its unique salt tolerance and strong preference for ammonium (NH4+) as a nitrogen (N) source. We here examined whether Spartinas unique preference for NH4+ results in improved performance under drought stress. Manipulative greenhouse experiments were carried out to measure the effects of variable water availability and inorganic N sources on plant performance (growth, photosynthesis, antioxidant, and N metabolism). Drought strongly reduced leaf number and area, plant fresh and dry weight, and photosynthetic activity on all N sources, but the reduction was most pronounced on NH4+. Indeed, the growth advantage seen on NH4+ in the absence of drought, producing nearly double the biomass compared to growth on NO3, was entirely obliterated under both intermediate and severe drought conditions (50 and 25% field capacity, respectively). Both fresh and dry weight became indistinguishable among N sources under drought. Major markers of the antioxidant capacity of the plant, the activities of the enzymes superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, showed higher constitutive levels on NH4+. Catalase and glutathione reductase were specifically upregulated in NH4+-fed plants with increasing drought stress. This upregulation, however, failed to protect the plants from drought stress. Nitrogen metabolism was characterized by lower constitutive levels of glutamine synthetase in NH4+-fed plants, and a rise in glutamate dehydrogenase (GDH) activity under drought, accompanied by elevated proline levels in leaves. Our results support postulates on the important role of GDH induction, and its involvement in the synthesis of compatible solutes, under abiotic stress. We show that, despite this metabolic shift, S. alternifloras sensitivity to drought does not benefit from growth on NH4+ and that the imposition of drought stress equalizes all N-source-related growth differences observed under non-drought conditions.

Introduction

Under natural conditions of growth and development, plants are inevitably exposed to multiple stresses, such as drought, salinity, flooding, mineral deficiencies, and toxicity (Ben Hamed et al., 2013). Of these, drought is considered one of the most formidable challenges to agricultural productivity (Mahajan and Tuteja, 2005, Hessini et al., 2008, Hessini et al., 2009b), and the greatest losses in productivity occur in arid and semiarid regions, where, in addition to scarcity, the quality of irrigation water is often low (Fernández-Cirelli et al., 2009).

Drought inhibits plant growth by disturbing the uptake of ions and water, impeding N-metabolism, and causing oxidative stress (Gonzalez et al., 1998, Bhargava and Sawant, 2013). The extent of damage depends on plant genotype, the severity of the stress, and the type, quantity, and regime of fertilization (Hessini et al., 2009a, Waraich et al., 2011, Waraich et al., 2012). The use of fertilizer to enhance crop productivity has increased five-fold since the 1960s, and about 65% of it is used on cereals. However, inadequate or inefficient fertilization perturbs plant growth and contributes to soil degradation (Humbert et al., 2013), and it is predicted that access to fertilization will be one of the main challenges for crop production in drought-prone areas (Shiferaw et al., 2014).

Nitrogen (N), the most important macronutrient obtained by plant roots, is deficient in most soils, and in particular those in arid and semiarid regions (Hernández et al., 1997). It is critical to all principal metabolic processes, including those related to osmotic adjustment, and constitutes almost 80% of the total nutrients absorbed by plant roots (Marschner, 1995). Plants take up N mainly in two forms: nitrate (NO3) and ammonium (NH4+), or as mixtures of the two. Great differences exist between species in their preference for the sources of N, with most species growing best on either NO3 or a mixed N source (Kronzucker et al., 1999), while only few perform best on NH4+ (Kronzucker et al., 1997, Britto and Kronzucker, 2002, Britto and Kronzucker, 2013).

Plant response to N fertilization under drought conditions varies with plant species, climate, N source, and fertilization regime (Waraich et al., 2011). Nitrate may not always be beneficial under drought, as it can accumulate in plant leaves without contributing to biomass or to increasing yield (Martinoia et al., 1981, Bernguer et al., 2009). However, the NO3 ion can also serve as an electron sink and potentially alleviate photosystem stress under water limitation conditions (Yi et al., 2014). Plants with high tissue NO3 levels also lose nutritional value because, when consumed in excess, NO3 can be harmful for human and livestock health (Britto and Kronzucker, 2002, Hessini et al., 2009b). Thus, there is interest in identification and development of drought-tolerant plant genotypes able to utilize NH4+ as their principal N source. Indeed, the addition of NH4+ to the nutrient solution has been reported to mitigate the adverse effects of drought on growth and development of rice (Gao et al., 2010). NH4+ has also been reported to mitigate the effects of salt stress on Hordeum vulgare, Citrange carrizo, and Spartina alterniflora (Kant et al., 2007, Fernández-Crespo et al., 2012, Hessini et al., 2013), although others have observed the opposite effect, as, for instance, in pea (Speer et al., 1994, Speer and Kaiser, 1994).

Although the mechanism by which NH4+ may enhance plant tolerance to osmotic stress is not clear, several authors consider it a result of: (i) NH4+ assimilation carrying a lower energy cost than that of NO3 (Kant et al., 2007); (ii) increased plant water absorption (Gao et al., 2010); (iii) the activation of antioxidant enzymes responsible for some mechanisms of early acclimation to stress (Misra and Gupta, 2006, Fernández-Crespo et al., 2012).

Spartina alterniflora is an interesting test species due to its C4 photosynthetic habit and high tolerance for environmental stresses. Due to these characteristics, Spartina is sometimes an invasive species that can disturb natural ecosystems. In this study, we explore the mechanism for drought tolerance in this species and report the effects of ammonium nutrition on the species in the light of the responsiveness of its antioxidant systems and shifts in N metabolism that may be required for acquisition of drought tolerance.

Section snippets

Plant material and propagation

The plants used in this experiment were obtained from 25-cm-high cuttings transplanted into 4-L blow-moulded pots (one cutting per pot) filled with sandy soil and irrigated with Hewitt (1966) nutrient solution for one month under well-watered conditions, in a greenhouse with an average air temperature of 25/18 °C day/-night, an air relative humidity ranging between 65 and 90%, an average irradiance at mid-day of ∼900/1800 μmol m−2 s−1 PAR, and a natural photoperiod of 12–15 h. In order to prevent

Growth

Under well-watered conditions (100% FC), plant biomass accrual responded strongly to the N source present in the root medium. The biomass of NO3-fed plants was only half that of those fed with NH4+, while NH4NO3-fed plants had intermediate biomass (Fig. 1). Under drought conditions (soil moisture 50 or 25% FC), plant biomass accumulation became similar on all three N-source treatments, and at 50% FC no significant differences from control, NO3-fed, plants were observed.

The effect of drought

Discussion

Drought is a major stress factor for most plants, even for C4 species, which have a water-use efficiency significantly superior to that of C3 plants under arid conditions, being able to maintain stomatal closure when water availability is low (Sage, 2004, Osborne and Beerling, 2006). S. alterniflora, a C4 grass, is able to thrive on, acclimate to, and tolerate salinity stress well (Hessini et al., 2013). It is also unique in that it grows best on NH4+ as an N source, rather than nitrate or

Conclusion

Although Spartina alterniflora is able to thrive on, acclimate to, and tolerate both ammonium and salinity stresses, it is unable to tolerate drought, even when provided with its preferred N form, NH4+. Indeed, in contrast to performance under salt stress, drought imposition completely nullifies any of the growth advantages observed in this C4 grass under normal conditions when provided with NH4+ as an N source. The sensitivity of the species to drought is in part due to low constitutive levels

Author contributions

HK and CC carried out experimental and analysis work.

HK, CC and AC: design and interpretation of all experiments.

HK and KHJ wrote the manuscript.

Acknowledgements

This work was supported by the Tunisian Ministry of Higher Education and Scientific Research (LR10CBBC02). Special thanks to Dr. Stephen Houghton for improving the English of the manuscript.

References (87)

  • R. Mittler

    Oxidative stress, antioxidants and stress tolerance

    Trends Plant Sci.

    (2002)
  • J. Nimptsch et al.

    Ammonia triggers the promotion of oxidative stresss in the aquatic macrophyte Myriophyllum mattogrossense

    Chemosphere

    (2007)
  • K. Rios-Gonzalez et al.

    The activity of antioxidant enzymes in maize and sunflower seedlings as affected by salinity and different nitrogen sources

    Plant Sci.

    (2002)
  • B. Shiferaw et al.

    Managing vulnerability to drought and enhancing livelihood resilience in sub-Saharan Africa: technological, institutional and policy options

    Weather Clim. Extr.

    (2014)
  • Z.Q. Wang et al.

    Glutamine synthetase and glutamate dehydrogenase contribute differentially to proline accumulation in leaves of wheat (Triticum aestivum) seedlings exposed to different salinity

    J. Plant Physiol.

    (2007)
  • C. Wang et al.

    Effects of ammonium on the antioxidative response in Hydrilla verticillata (L.f.) Royle plants

    Ecotox. Environ. Safe

    (2010)
  • I. Ariz et al.

    Changes in the C/N balance caused by increasing external ammonium concentrations are driven by carbon and energy availabilities during ammonium nutrition in pea plants: the key roles of asparagine synthetase and anaplerotic enzymes

    Physiol. Plant

    (2013)
  • M. Ashraf et al.

    Photosynthesis under stressful environments: an overview

    Photosynthetica

    (2013)
  • C. Barth et al.

    A mutation in GDP-mannose pyrophosphorylase causes conditional hypersensitivity to ammonium, resulting in Arabidopsis root growth inhibition, altered ammonium metabolism, and hormone homeostasis

    J. Exp. Bot.

    (2010)
  • R.F. Beers et al.

    Spectrophotometric method for measuring the breakdown of hydrogen peroxide by catalase

    J. Biol. Chem.

    (1952)
  • K. Ben Hamed et al.

    Physiological response of halophytes to multiple stresses

    Funct. Plant Biol.

    (2013)
  • R. Bendixen et al.

    Difference in zeaxanthin formation in nitrate- and ammonium-grown Phaseolus vulgaris

    Physiol. Plant

    (2001)
  • P. Bernguer et al.

    Nitrogen fertilization of irrigated maize under Mediterranean conditions

    Eur. J. Agron.

    (2009)
  • S. Bhargava et al.

    Drought stress adaptation: metabolic adjustment and regulation of gene expression

    Plant Breeding

    (2013)
  • Bouyoucos

    Les propriétés physiques du sol dépendent de sa texture et de sa structure

    Les Bases De La Production végétale. Tome 1

    (1983)
  • D.T. Britto et al.

    Ecological significance and complexity of N-source preference in plants

    Ann. Bot.

    (2013)
  • R. Cantera et al.

    Acidifying product as a source of stabilized ammonia nitrogen under greenhouse conditions

  • F.J. Castillo et al.

    Peroxidase release induced by ozone in sedum album leaves

    Plant Physiol.

    (1984)
  • M.D. Domínguez-Valdivia et al.

    Nitrogen nutrition and antioxidant metabolism in ammonium-tolerant and −sensitive plants

    Plant Physiol.

    (2008)
  • E.A. Edwards et al.

    Subcellular distribution of multiple forms of glutathione reductase in leaves of pea (Pisum sativum L.)

    Planta

    (1990)
  • G.E. Edwards et al.

    Single cell C4 photosynthesis versus the dual-cell (Kranz) paradigm

    Ann. Rev. Plant Biol.

    (2004)
  • R. El Omari et al.

    Ammonium tolerance and the regulation of two cytosolic glutamine synthetases in the roots of sorghum

    Funct. Plant Biol.

    (2010)
  • A. Fernández-Cirelli et al.

    Environmental effects of irrigation in arid and semi-arid regions

    Chil. J. Agric. Res.

    (2009)
  • C.H. Foyer et al.

    Drought-induced effects on nitrate reductase activity and mRNA and on the coordination of nitrogen and carbon metabolism in maize leaves

    Plant Physiol.

    (1998)
  • C.H. Foyer et al.

    Markers and signals associated with nitrogen assimilation in higher plants

    J. Exp. Bot.

    (2003)
  • J. Frew et al.

    Spectrophotometric determination of hydrogen peroxide and organic hydroperoxides at low concentrations in aqueous solution

    Anal. Chim. Acta

    (1983)
  • Y. Gao et al.

    Ammonium nutrition increases water absorption in rice

    Plant Soil

    (2010)
  • T.P. Garnett et al.

    Simultaneous measurement of ammonium, nitrate and proton fluxes along the length of eucalypt roots

    Plant Soil

    (2001)
  • J. Gerendas et al.

    Physiological and biochemical processes related to ammonium toxicity in higher plants

    Z Pflanzenernähr Bodenkd

    (1997)
  • O. Ghannoum

    C4 photosynthesis and water stress

    Ann. Bot.

    (2009)
  • E.M. Gonzalez et al.

    Water-deficit effects on carbon and nitrogen metabolism of pea nodules

    J. Exp. Bot.

    (1998)
  • R.G. Groat et al.

    Root nodules enzymes of ammonium assimilation in alfalfa (Medicago sativa L.)

    Plant Physiol.

    (1981)
  • S. Guo et al.

    Different apparent CO2 compensation points in nitrate- and ammonium-grown Phaseolus vulgaris and the relationship to non-photorespiratory CO2 evolution

    Physiol. Plant

    (2005)
  • Cited by (25)

    • Growth and nitrogen metabolism in Sophora japonica (L.) as affected by salinity under different nitrogen forms

      2022, Plant Science
      Citation Excerpt :

      indicated that some conifer seedlings grown in hydroponic experiments prefer to take up NH4+ over NO3−, whereas their mature trees in plantations assimilated NO3− as efficiently as NH4+ from soils. The N source preference performs differently among plant species, developmental stages and environmental conditions (Camalle et al., 2020; Hessini et al., 2017). However, this phenomenon has not been studied in many species, especially forest trees, which can reflect their functional niche within an ecosystem.

    View all citing articles on Scopus
    View full text