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. 2024 Dec 6;25(23):13116.
doi: 10.3390/ijms252313116.

Growth, Quality, and Nitrogen Metabolism of Medicago sativa Under Continuous Light from Red-Blue-Green LEDs Responded Better to High Nitrogen Concentrations than Under Red-Blue LEDs

Ren Chen  1 , Yanqi Chen  2   3 , Kunming Lin  2   3 , Yiming Ding  1 , Wenke Liu  1   2   3 , Shurong Wang  1
Affiliations

Growth, Quality, and Nitrogen Metabolism of Medicago sativa Under Continuous Light from Red-Blue-Green LEDs Responded Better to High Nitrogen Concentrations than Under Red-Blue LEDs

Ren Chen et al. Int J Mol Sci. .

Abstract

Alfalfa is a widely grown forage with a high crude protein content. Clarifying the interactions between light quality and nitrogen level on yield and nitrogen metabolism can purposely improve alfalfa productivity in plant factories with artificial light (PFAL). In this study, the growth, quality, and nitrogen metabolism of alfalfa grown in PFAL were investigated using three nitrate-nitrogen concentrations (10, 15, and 20 mM, labeled as N10, N15, and N20) and continuous light (CL) with two light qualities (red-blue and red-blue-green light, labeled as RB-C and RBG-C). The results showed that the adaptation performance of alfalfa to nitrogen concentrations differed under red-blue and red-blue-green CL. Plant height, stem diameter, leaf area, yield, Chl a + b, Chl a, Chl b, crude protein contents, and NiR activity under the RB-CN15 treatment were significantly higher than RB-CN10 and RB-CN20 treatments. The RB-CN20 treatment showed morphological damage, such as plant dwarfing and leaf chlorosis, and physiological damage, including the accumulation of proline, H2O2, and MDA. However, the difference was that under red-blue-green CL, the leaf area, yield, and Chl a + b, carotenoid, nitrate, and glutamate contents under RBG-CN20 treatment were significantly higher than in the RBG-CN10 and RBG-CN15 treatments. Meanwhile, the contents of soluble sugar, starch, and cysteine were significantly lower. However, the crude protein content reached 21.15 mg·g-1. The fresh yield, dry yield, stomatal conductance, leaf area, plant height, stem diameter, crude protein, GS, and free amino acids of alfalfa were positively correlated with increased green light. In addition, with the increase in nitrogen concentration, photosynthetic capacity, NiR, and GOGAT activities increased, promoting growth and improving feeding value. The growth, yield, photosynthetic pigments, carbon, nitrogen substances, and enzyme activities of alfalfa were significantly affected by the interaction between nitrogen concentration and light quality, whereas leaf/stem ratio and DPPH had no effect. In conclusion, RB-CN15 and RBG-CN20 are suitable for the production of alfalfa in PFAL, and green light can increase the threshold for the nitrogen concentration adaptation of alfalfa.

Keywords: alfalfa; crude protein; enzyme activity; plant factory with artificial light (PFAL); yield.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Appearance of alfalfa under three nitrogen concentrations and CL with two light qualities.
Figure 2
Figure 2
Growth characteristics and yield of alfalfa under three nitrogen concentrations with red–blue and red–blue–green CL. (A) Plant height, (B) stem diameter, (C) leaf area, (D) fresh yield, (E) dry yield, (F) fresh/dry ratio, (G) leaf/stem ratio, and (H) specific leaf area. Data are means ± SE; n = 5. Error bars with different letters show a significant difference (p < 0.05).
Figure 3
Figure 3
Photosynthetic pigment content, stomatal conductance, and Fv/Fm of alfalfa leaves under red and blue light and green light instead of red light. (A) Chl a + b content, (B) Chl a content, (C) Chl b content, (D) carotenoid content, (E) stomatal conductance, and (F) Fv/Fm. Data are means ± SE; n = 5. Error bars with different letters show a significant difference (p < 0.05).
Figure 4
Figure 4
Soluble sugar (A), sucrose (B), starch (C), soluble protein (D), free amino acid (E), and crude protein (F) contents in alfalfa under three nitrogen concentrations and CL with two light qualities. Error bars with different letters show a significant difference (p < 0.05).
Figure 5
Figure 5
DPPH free radical clearance rate (A), Proline (B), H2O2 (C), and MDA (D) contents in alfalfa under three nitrogen concentrations and CL with two light qualities. Error bars with different letters show a significant difference (p < 0.05).
Figure 6
Figure 6
Nitrate (A) and ammonium (B) contents and activities of NR (C) and NiR (D) in alfalfa under three nitrogen concentrations and CL with two light qualities. Error bars with different letters show a significant difference (p < 0.05).
Figure 7
Figure 7
Glutamate (A), cysteine (B), and lysine (C) contents and activities of GOGAT (D), GS (E), GDH (F), CS (G), and AK (H) in alfalfa under three nitrogen concentrations and CL with two light qualities. Error bars with different letters show a significant difference (p < 0.05).
Figure 8
Figure 8
Correlation and heatmap analysis of growth characteristics, yield, photosynthetic pigment content, stomatal conductance, and Fv/Fm under three nitrogen concentrations and CL with two light qualities. Note. * Significant at the p < 0.05 level of probability, ** significant at the p < 0.01 level of probability, *** significant at the p < 0.001 level of probability.
Figure 9
Figure 9
Correlation and heatmap analysis of carbon and nitrogen substances and enzyme activities under three nitrogen concentrations and CL with two light qualities. Note. * Significant at the p < 0.05 level of probability, ** significant at the p < 0.01 level of probability, *** significant at the p < 0.001 level of probability.
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