Ammonium/nitrate ratio affects the growth and glucosinolates content of pakchoi

Yang, Jing; Zhu, Biao; Ni, Xiaolei; He, Yong

doi:10.1590/S0102-053620200302

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Research • Hortic. Bras. 38 (3) • 2020 • https://doi.org/10.1590/S0102-053620200302 copy

Ammonium/nitrate ratio affects the growth and glucosinolates content of pakchoi

Relação amônio/nitrato afeta o crescimento e o conteúdo de glucosinolatos do pakchoi

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Nitrogen (N) strongly affects plant growth. However, little is known about the effects of the ammonium/nitrate ratio on pakchoi (Brassica rapa), especially its glucosinolates (GSs) contents which are involved in plant defense and many of them benefit to human health. The aim of this study was to evaluate the effects of a constant N supply (8 mM) but with five ammonium/nitrate ratios (namely 0/8 mM, 2/6 mM, 4/4 mM, 6/2 mM and 8/0 mM) on the growth of pakchoi in a hydroponic system in 2 years. In both years, a higher biomass (dry weight) was in the 4/4 and 2/6 ammonium/nitrate treatments (2.3 and 2.2-fold compared to 8/0, respectively), with no significant difference in biomass between these two treatments. The biomass then decreased with increasing proportions of ammonium in the N supply from more than 10 g/pot to below 5 g/pot. The N and sulfur contents were strongly affected in the sole nitrate or ammonium treatments, as were the contents of chlorophyll, lutein, and β-carotene. Most of the individual glucosinolates (GSs) detected in pakchoi showed the highest concentrations in the sole ammonium treatment. The ammonium/nitrate ratio also affected the types of GSs. The highest proportion of indolyl GSs and the lowest proportion of aromatic GSs were in the sole ammonium treatment. We concluded that a high ammonium level decreases the biomass but increases the GSs concentrations in pakchoi. Further studies are required to explore the difference in GSs metabolism among plants supplied with different ammonium/nitrate ratios.

Keywords:
Brassica rapa; biomass; nitrogen form; secondary metabolites

NH₄ ⁺-N/NO₃ ^--N (mM)	Shoot dry weight (g pot^-1)		Shoot dry matter content (%)		Root dry weight (g pot^-1)
NH₄ ⁺-N/NO₃ ^--N (mM)	1^st	2^nd	1^st	2^nd	1^st	2^nd
0/8	8.96 ± 0.96 bc^b	9.12 ± 2.20 ab	6.07 ± 0.39 d	5.72 ± 0.64 b	1.27 ±0.09a	1.41 ±0.34 b
2/6	10.05 ± 1.16 ab	10.37 ± 0.23 a	6.13 ± 0.21 d	5.96 ± 0.70 b	1.18 ± 0.12 a	1.83 ± 0.20 a
4/4	10.70 ± 1.73 a	7.78 ± 1.76 ab	6.85 ± 0.30 c	6.36 ± 0.78 b	1.28 ± 0.26 a	1.37 ± 0.22 b
6/2	7.80 ± 0.26 c	6.69 ± 1.76 bc	7.42 ± 0.13 b	6.72 ± 0.12 b	1.06 ± 0.05 a	1.48 ± 0.21 ab
8/0	4.62 ± 0.75 d	4.81 ± 0.58 c	9.18 ± 0.35 a	10.74 ± 1.06 a	0.56 ± 0.07 b	0.49 ± 0.08 c

NH₄ ⁺-N/NO₃-N (mM)	Nitrogen	Phosphorus	Potassium	Calcium	Magnesium	Sulphur
NH₄ ⁺-N/NO₃-N (mM)	(mg g^-1 DW)
0/8	47.23 ± 2.96 a	5.71 ± 0.32 c	29.08 ± 0.21 a	4.75 ± 0.05 ab	2.73 ± 0.11 a	5.67 ± 0.09 b
2/6	38.93 ± 2.65 c	6.43 ± 0.42 b	26.33 ± 1.13 b	4.86 ± 0.03 a	2.64 ± 0.07 a	5.75 ± 0.36 b
4/4	41.33 ± 2.42 bc	6.57 ± 0.09 b	23.69 ± 0.74 c	4.83 ± 0.13 ab	2.49 ± 0.13 b	5.68 ± 0.23 b
6/2	42.19 ± 1.00 bc	6.27 ± 0.14 b	23.83 ± 0.37 c	4.72 ± 0.04 b	2.08 ± 0.07 c	5.43 ± 0.29 b
8/0	44.08 ± 2.92 ab	7.68 ± 0.26 a	24.38 ± 0.60 c	4.73 ± 0.08 b	2.06 ± 0.05 c	7.28 ± 0.47 a

NH₄ ⁺-N/NO₃ ^--N (mM)		Glucoalyssin	Gluconapin	Glucobrassicanapin	Glucobrassicin
NH₄ ⁺-N/NO₃ ^--N (mM)		(μmol g^-1 DW)
1^st	0/8	0.16 ± 0.03 d ^b	3.12 ± 0.47 c	1.48 ± 0.08 c	0.23 ± 0.03 bc
	2/6	0.17 ± 0.06 d	3.50 ± 0.71 c	1.43 ± 0.29 c	0.18 ± 0.03 c
	4/4	0.24 ± 0.04 c	3.61 ± 0.50 c	1.77 ± 0.16 bc	0.18 ± 0.03 c
	6/2	0.30 ± 0.06 b	4.76 ± 1.30 b	2.17 ± 0.53 b	0.27 ± 0.04 b
	8/0	0.68 ± 0.10 a	7.25 ± 1.20 a	3.87 ± 0.82 a	0.71 ± 0.15 a
2^nd	0/8	0.12 ± 0.04 b	4.92 ± 0.15 a	1.47 ± 0.60 bc	0.19 ± 0.06 c
	2/6	0.17 ± 0.06 b	2.74 ± 0.68 bc	1.22 ± 0.17 c	0.10 ± 0.04 c
	4/4	0.17 ± 0.03 b	2.54 ± 0.32 c	1.02 ± 0.05 c	0.07 ± 0.02 c
	6/2	0.18 ± 0.01 b	4.12 ± 1.08 ab	1.89 ± 0.27 ab	0.51 ± 0.09 b
	8/0	0.35 ± 0.10 a	4.35 ± 1.18 a	2.15 ± 0.30 a	0.72 ± 0.16 a
NH₄ ⁺-N/NO₃ ^--N (mM)		Gluconasturtiin	4-methoxyglucobrassicin		Neoglucobrassicin
NH₄ ⁺-N/NO₃ ^--N (mM)		(μmol g^-1 DW)
1^st	0.23 ± 0.03 bc	0.72 ± 0.14 a	0.032 ± 0.008 b		0.29 ± 0.12 bc
	0.18 ± 0.03 c	0.47 ± 0.11 b	0.021 ± 0.004 c		0.23 ± 0.06 c
	0.18 ± 0.03 c	0.70 ± 0.11 a	0.026 ± 0.010 bc		0.34 ± 0.09 bc
	0.27 ± 0.04 b	0.65 ± 0.15 a	0.045 ± 0.017 a		0.40 ± 0.08 b
	0.71 ± 0.15 a	0.82 ± 0.22 a	0.035 ± 0.014 b		1.19 ± 0.21 a
2^nd	0.19 ± 0.06 c	0.37 ± 0.10 a	0.018 ± 0.004 a		0.18 ± 0.01c
	0.10 ± 0.04 c	0.31 ± 0.02 ab	0.012 ± 0.000 b		0.13 ± 0.03 cd
	0.07 ± 0.02 c	0.22 ± 0.03 b	0.011 ± 0.001 b		0.12 ± 0.04 d
	0.51 ± 0.09 b	0.30 ± 0.02 ab	0.022 ± 0.001 a		0.26 ± 0.01 b
	0.72 ± 0.16 a	0.36 ± 0.06 a	0.020 ± 0.005 a		0.45 ± 0.03 a

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[TFN1] 1^st= first year; 2^nd= second year. ^aData are presented as mean ± standard deviation (first year: n= 5, second year: n= 4). ^bMeans followed by different letters in each column were significantly different (p<0.05).