Ionic homeostasis, biochemical components and yield of Italian zucchini under nitrogen forms and salt stress.

C S Fernandes,N S Dias,F V S Sá,L B L Reges,M Ferreira Neto,A A Silva,E P Paiva,A S Melo,H R Gheyi

doi:10.1590/1519-6984.233567

Abstract

This research was carried out aiming at evaluating the effects of nitrate and ammonium ions on nutrient accumulation, biochemical components and yield of Italian zucchini (cv. Caserta) grown in a hydroponic system under salt stress conditions. The experiment was carried out in a greenhouse utilizing an experimental design in randomized blocks, arranged in a 2 x 5 factorial scheme, with 4 replications. The treatments consisted of two forms of nitrogen (nitrate - NO3- and ammonium - NH4+) and 5 electrical conductivity levels of irrigation water (ECw) (0.5, 2.0, 3.5, 5.0 and 6.5 dS m-1). The analysis of the results indicated that supply of N exclusively in NH4+ form promotes greater damage to the leaf membrane and reduction in accumulation of macronutrients and higher Na+/K+, Na+/Ca++ and Na+/Mg++ ratios in the shoots of zucchini plants. Electrical conductivity of irrigation water above 2.0 dS m-1 reduces the accumulation of nutrients in shoot and yield of Italian zucchini plant. The toxicity of NH4+ under Italian zucchini plants overlap the toxicity of the salinity, since its fertilization exclusively with this form of nitrogen inhibits its production, being the NO3- form the most suitable for the cultivation of the species.

Highlights

Nitrogen is a limiting factor for crop growth and yield, since it is essential and required in large quantities by most plants (McAllister et al, 2012; Medeiros et al, 2016)
The plants fertilized with NO3- had higher accumulation of macronutrients than those fertigated with nutrient solution containing NH4+, with increments of 25.5%, 54.0%, 61.4%, 165.3% and 215.9% for N, P, K, Ca and Mg, respectively (Figures 1A-E)
Salt stress is caused by excess ions in the rhizosphere, limiting water extraction by the roots and reducing

Summary

Introduction

Nitrogen is a limiting factor for crop growth and yield, since it is essential and required in large quantities by most plants (McAllister et al, 2012; Medeiros et al, 2016). The higher energy expenditure of the plant to assimilate NO3- occurs because, unlike NH4+ which is directly incorporated into amino acids by the enzymes glutamine synthase (GS) and glutamate synthase (GOGAT). Most species prefer to absorb it in the form of NO3-, there is a greater energy expenditure for its assimilation in this case (McAllister et al, 2012).

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