Nitrogen use efficiencies of spring barley grown under varying nitrogen conditions in the field and growth chamber

Abstract

Background and aims: Nitrogen-use efficiency (NUE) of cereals needs to be improved by nitrogen (N) management, traditional plant breeding methods and/or biotechnology, while maintaining or, optimally, increasing crop yields. The aims of this study were to compare spring-barley genotypes grown on different nitrogen levels in field and growth-chamber conditions to determine the effects on N uptake (NUpE) and N utilization efficiency (NUtE) and ultimately, NUE.

Methods: Morphological characteristics, seed yield and metabolite levels of 12 spring barley (Hordeum vulgare) genotypes were compared when grown at high and low nitrogen levels in field conditions during the 2007 and 2008 Canadian growing seasons, and in potted and hydroponic growth-chamber conditions. Genotypic NUpE, NUtE and NUE were calculated and compared between field and growth-chamber environments.

Key results: Growth chamber and field tests generally showed consistent NUE characteristics. In the field, Vivar, Excel and Ponoka, showed high NUE phenotypes across years and N levels. Vivar also had high NUE in growth-chamber trials, showing NUE across complex to simplistic growth environments. With the high NUE genotypes grown at low N in the field, NUtE predominates over NUpE. N metabolism-associated amino acid levels were different between roots (elevated glutamine) and shoots (elevated glutamate and alanine) of hydroponically grown genotypes. In field trials, metabolite levels were different between Kasota grown at high N (elevated glutamine) and Kasota at low N plus Vivar at either N condition.

Conclusions: Determining which trait(s) or gene(s) to target to improve barley NUE is important and can be facilitated using simplified growth approaches to help determine the NUE phenotype of various genotypes. The genotypes studied showed similar growth and NUE characteristics across field and growth-chamber tests demonstrating that simplified, low-variable growth environments can help pinpoint genetic targets for improving spring barley NUE.

Fig. 1.

Morphological characteristics of four spring-barley genotypes grown in Sunshine mix #4 in a growth chamber, at four different N concentrations (25, 50, 75 and 100 % N). In (A) and (B), measurements were taken at anthesis, when 50 % of the plants for each genotype showed a spike at the top of the boot. This was at 54 DAS for Morex, 67 DAS for Vivar and Kasota and 75 DAS for CDC-Copeland. (A) Shoot dry weight; (B) flag leaf width. In (C) and (D) measurements were taken at plant maturity: (C) shoot dry weight, (D) seed weight. Values represent the average ± s.e. of six independent plant samples. Different letters above the bars indicate significant differences between plants grown at different N concentrations (P ≤ 0·05). Asterisks indicate genotypes that are not significantly different within a certain measured trait.

Fig. 2.

Morphological characteristics of four spring-barley genotypes grown in a hydroponic growth chamber, at four different N concentrations (0·5, 2, 4 and 8 mm nitrate): (A) shoot dry weight; (B) root dry weight; (C) total dry weight. Measurements were taken just prior to anthesis at 42 DAG. Values represent the average ± s.e. of three independent plant samples. Different letters above the bars indicate significant differences between plants grown at different N concentrations (P ≤ 0·05). Asterisks indicate genotypes which are not significantly different within a certain measured trait. Genotypes which have a cross and an asterisk show significant differences between them (P ≤ 0·05).

Fig. 3.

Principal component analysis (PCA) of amino acid metabolite levels from (A) the shoots of Vivar and Kasota genotypes grown in field conditions at low and high supplied N in the Canadian 2008 growing season (V-Lo, V-Hi, K-Lo and K-Hi) and (B) the roots and shoots of Vivar and Kasota genotypes grown hydroponically at three different concentrations of supplied N (0·5, 4 and 8 mm nitrate; V0·5, V4, V8, K0·5, K4, K8). Values represent the average ± s.e. of four independent plant samples for the field-grown barley and three independent plant samples for the hydroponically grown barley (sample number given at the end of each label).