Nitrogen fertilization affects yields and storage compound contents in seeds of field-grown soybeans cv Enrei (Glycine max. L) and its super-nodulating mutant En-b0-1 through changing N₂ fixation activity of the plants

Figures & data

Table 1. Effects of N fertilization on the seed growth of the three soybean genotypes with different nodulation abilities.

Genotype	N Treat.	Seed Wt. (g)	No./plants
En1282	L-L	0.18 (0.03) ^f	51.6 (18.4) ^e,f
	H-L	0.22 (0.05) ^e,f	118.1 (29.0) ^b
	L-H	0.27 (0.02) ^b–d	117.7 (22.7) ^b
	H-H	0.28 (0.03) ^a–c	128.7 (29.8) ^a,b
Enrei	L-L	0.30 (0.02) ^a	118.2 (28.7) ^b
	H-L	0.26 (0.01) ^c–e	93.0 (34.9) ^b–d
	L-H	0.30 (0.02) ^a,b	158.5 (28.3) ^a
	H-H	0.28 (0.02) ^b,c	108.7 (37.3) ^b,c
En-b0-1	L-L	0.23 (0.03) ^e	31.1 (13.9)^f
	H-L	0.23 (0.02) ^d,e	43.6 (17.2) ^e,f
	L-H	0.25 (0.03) ^c–e	56.8 (22.5)^d–f
	H-H	0.25 (0.01) ^c–e	77.2 (21.4) ^c–e
ANOVA:
Genotype		p < 0.001	p < 0.001
N level		p < 0.001	p < 0.001
Interaction		p < 0.001	p < 0.001

Different letters within columns indicate significant differences (p < 0.05, Tukey’s HSD test). Parentheses indicate the SD.

Table 2. The σ¹⁵N values of mature seeds from plants of three genotypes of soybean.

	N Treatment
Genotype	L-L	H-L	L-H	H-H
En1282	3.36	2.57	1.22	1.07
	(0.60)	(0.51)	(0.66)	(0.14)
Enrei	−0.20	2.12	0.33	1.88
	(0.36)	(1.36)	(0.14)	(0.36)
En-b0-1	−0.61	1.46	1.06	1.69
	(0.22)	(0.02)	(0.09)	(0.22)

The σ¹⁵N value of a urea coated slow release nitrogen fertilizer (Meister 15) was −1.41.

^†σ¹⁵N values: Averages of duplicated samples. Parentheses indicate the SD (n = 2).

Figure 1. Effects of the N fertilization on the seed yields of three genotypes of soybean. Symbols indicate the types of N treatment where plants were grown: white, L-L; horizontal stripe, H-L; vertical stripe, L-H; black, H-H. Different letters indicate significant differences between genotypes and N treatments.

Figure 2. Effects of the N fertilization on the protein content and oil content in seeds from plants of three soybean genotypes. (a): The relationship between the protein content and the seed weight. (b): The relationship between the oil content and the seed weight. (c): The relationship between the oil content and the protein content. Shapes of symbols circles, squares, and triangles indicate the genotypes, En1282, Enrei and En-b0-1, respectively. Patterns inside symbols indicate the types of N treatment described in Figure 1 legend. The correlation coefficients between the protein content and seed weight from the En1282 and Enrei plants were 0.982 and 0.907, respectively. The significance levels were 0.02 and 0.10 for En1282 and Enrei, respectively. The correlation coefficient between the protein content and the oil content from the En-b0-1 plants was −0.924 (p = 0.10).

Figure 3. Interrelationships between the protein content and oil content in seeds from plants of three soybean genotypes.

Figure 4. Effects of the N fertilization on the amounts of protein and oil per seed from plants of the three soybean genotypes. Shapes of symbols indicate the same genotype as those described in Figure 2 legend. Numbers beside marks indicate types of N plots where plants were grown as follows: 1: L-L, 2: H-L, 3: L-H, and 4: H-H. The dotted line indicates the coefficient line between the amount of oil per seed and the amount of protein per seed from En1282 plants (p = 0.01).

Table 3. Contribution of N derived from N₂ fixation of plants of two nodulating genotypes grown on fields where had different N treatments (%Ndfa).

	N Treatments
Genotype	L-L	H-L	L-H	H-H
Enrei	106.1	17.6	73.1	−75.0
En-b0-1	118.1	43.3	13.3	−57.3

The values were obtained by substituted σ¹⁵N values into Equation (1)(1) $\begin{array}{rl}& \mathrm{\%}\mathrm{N}\mathrm{d}\mathrm{f}{\mathrm{a}}_{\mathrm{i}-\mathrm{i}\mathrm{i}}=({\sigma }^{15}\mathrm{N}\mathrm{o}\mathrm{f}\mathrm{E}\mathrm{n}1282_{\mathrm{i}-\mathrm{i}\mathrm{i}}-{\sigma }^{15}\mathrm{N}\mathrm{o}\mathrm{f}\mathrm{E}\mathrm{n}\mathrm{r}\mathrm{e}{\mathrm{i}}_{\mathrm{i}-\mathrm{i}\mathrm{i}}\\ & \mathrm{o}\mathrm{r}\mathrm{E}\mathrm{n}\text{-}\mathrm{b}0\text{-}{1}_{\mathrm{i}-\mathrm{i}\mathrm{i}})/({\sigma }^{15}\mathrm{N}\mathrm{o}\mathrm{f}\mathrm{E}\mathrm{n}1282_{\mathrm{i}-\mathrm{i}\mathrm{i}}-{\sigma }^{15}\mathrm{N}\mathrm{o}\mathrm{f}\mathrm{a}\mathrm{i}\mathrm{r})\mathrm{x}100\end{array}$(1) described in the text.

Table 4. The ratios and amounts of N originated from the two origins, soil+compound fertilizer, and CUSLNFs, in the total N in seeds from plants of non-nodulating genotype, En1282.

	Ratio, %		Amount, gN/plant
N Treat.	Soil+BF	CUSLNF	Soil+BF	CUSLNF	Sum
L-L	100	0	0.63	0	0.63
H-L^§	83.4	16.6	1.50	0.30	1.80
L-H^§	55.2	44.8	1.20	0.98	2.18
H-H	52.0	48.0	1.32	1.22	2.53

^§The values were calculated by the equation described in the text under the assumption that the two types of CUSLNF had the same σ¹⁵N values with that of Meister 15.

Table 5. The ratios and amounts of N originated from the three origins, soil+compound fertilizer, CUSLNFs, and N₂ fixation, in total N in seeds from plants of the two nodulating genotypes, Enrei and En-b0-1.

		Ratio, % Amount			gN/plant
N Treat.	Genotype	Soil+BF	SLNF	N2 fix.	Soil+BF	SLNF	N2 fix.	Sum
L-L	Enrei	10.1	0	89.9	0.28	0	2.48	2.75
	En-b0-1^†	0	0	100	0	0	0.53	0.53
H-L^§	Enrei	71.6	14.2	14.2	1.21	0.24	0.24	1.70
	En-b0-1	54.2	10.8	35.0	0.40	0.08	0.26	0.73
L-H^§	Enrei	28.2	22.9	48.9	0.97	0.79	1.68	3.43
	En-b0-1	50.3	40.8	8.9	0.53	0.43	0.09	1.06
H-H	Enrei^‡	76.9	71.0	−47.9	1.67	1.54	−1.04	2.17
		(52.0)	(48.0)	(0)	(1.13)	(1.04)	(0)	(2.17)
	En-b0-1^‡	71.0	65.5	−36.5	0.95	0.87	−0.49	1.33
		(52.0)	(48.0)	(0)	(0.64)	(0.69)	(0)	(1.33)

^†En-b0-1 plants grown on L-L soil; it was assumed that N was only from N₂ fixation.

^‡The numbers of each fraction of nitrogen origins in parentheses were calculated by the equation described in the text in the cases in which N₂ fixation did not work.

^§The values were calculated by the equation described in the text under the assumption that the two types of CUSLNF had the same σ¹⁵N values with that of Meister 15.