Effect of poly(γ-glutamic acid) on microbial community and nitrogen pools of soil

Figures & data

Table 1. PCR-DGGE conditions.

Target	Primer	PCR conditions
Bacteria	518R(5′-ATTACCGCGGCTGCTGG-3′)	94°C, 5 min; 30 cycles, 94°C, 45 s,
	GC ^a -338F(5′-ACTCCTACGGGAGGCAGC-3′)	60°C, 30 s; 72°C, 45 s; 72°C, 10 min
Fungi	NS1(5′-GTAGTCATATGCTTGTCTC-3′)	94°C, 4 min; 35 cycles, 94°C, 30 s;
	GC ^b -Fung(5′-ATTCCCCGTACCCGTTG-3′)	55°C, 30 s; 72°C, 1 min; 72°C, 10 min

Notes: ^a(CGC CCG CCG CGC GCG GCG GGC GGG GCG GGG GCA CGG GGG G).

^b(CGC CCG CCG CGC CCC GCG CCG GCC CGC CGC CCC CGC CCC).

Table 2. Effects of urea, glutamic acid and Poly(γ-glutamic acid) on the Chlorophyll contents and biomass of potted rapeseed at the late seedling stage.

Treatment	Chlorophyll contents (CCI)	Underground fresh weight per pot (g)	Above-ground fresh weight per pot (g)
T1	25.13 ± 2.90^c	2.01 ± 0.29^d	24.60 ± 3.03^c
T2	47.77 ± 3.37^b	2.58 ± 0.21^c	42.55 ± 1.15^b
T3	47.53 ± 3.26^b	2.74 ± 0.22^bc	43.21 ± 1.29^ab
T4	50.02 ± 2.38^ab	2.99 ± 0.23^abc	45.77 ± 1.88^ab
T5	51.60 ± 4.03^ab	3.15 ± 0.16^ab	46.13 ± 1.05^a
T6	55.43 ± 3.00^a	3.17 ± 0.28^ab	46.46 ± 1.37^a
T7	55.26 ± 1.70^a	3.20 ± 0.25^a	46.49 ± 2.55^a

Notes: Values are expressed as mean ± SD (n = 3). Statistical analysis was performed by Duncan's test (P < 0.05). Means in the same column with different letters are statistically different.

Table 3. Effects of urea, glutamic acid, and Poly(γ-glutamic acid) on yield and yield components of potted rapeseed at the maturity stage.

		Yield components
Treatment	Total biomass per pot (g)	Pod per pot	Seeds per pod	1000-grain weight (g)	Grain yield per pot (g)
T1	48.4 ± 1.9^d	160.7 ± 4.6^d	18.7 ± 0.6^b	3.78 ± 0.18^b	11.33 ± 0.54^c
T2	66.2 ± 2.0^c	188.0 ± 2.0^c	20.3 ± 1.5^ab	4.18 ± 0.14^a	15.94 ± 0.55^b
T3	68.2 ± 1.3^c	189.3 ± 2.3^bc	20.3 ± 0.6^ab	4.17 ± 0.13^a	16.04 ± 0.12^b
T4	71.5 ± 1.9^b	193.7 ± 1.2^ab	21.0 ± 1.0^a	4.17 ± 0.05^a	16.97 ± 0.24^ab
T5	73.6 ± 2.0^ab	195.0 ± 2.7^a	21.0 ± 1.0^a	4.22 ± 0.06^a	17.26 ± 0.69^a
T6	74.2 ± 1.6^ab	195.3 ± 2.3^a	21.3 ± 1.2^a	4.21 ± 0.06^a	17.54 ± 1.00^a
T7	75.6 ± 2.1^a	195.7 ± 2.3^a	21.3 ± 0.6^a	4.24 ± 0.07^a	17.69 ± 0.78^a

Notes: Values are expressed as mean ± SD (n = 3). Statistical analysis was performed by Duncan's test (P < 0.05). Means in the same column with different letters are statistically different.

Figure 1. Effect of poly(γ-glutamic acid) (γ-PGA) on the quantities of soil culturable bacteria (a), fungi (b), and actinomycetes (c). These values are expressed as mean ± SD (n = 3). Statistical analysis was performed by Duncan's test (P < 0.05). Means in the same column with different letters are statistically different. T₁, a check without urea; T₂, a check with urea only; T₃, urea mixed with 3 mg of glutamic acid per kilogram of soil; T₄, urea mixed with 3 mg of γ-PGA per kilogram of soil; T₅, urea mixed with 10 mg of γ-PGA per kilogram of soil; T₆, urea coated with γ-PGA (0.9%, m/m); and T₇, urea coated with γ-PGA (3.1%, m/m).

Figure 2. DGGE cluster analysis of 16S (a) and 18S rDNA (b) profiles of the soil microbial communities. T₁, a check without urea; T₂, a check with urea only; T₃, urea mixed with 3 mg of glutamic acid per kilogram of soil; T₄, urea mixed with 3 mg of poly(γ-glutamic acid) (γ-PGA) per kilogram of soil; T₅, urea mixed with 10 mg of γ-PGA per kilogram of soil; T₆, urea coated with γ-PGA (0.9%, m/m); and T₇, urea coated with γ-PGA (3.1%, m/m).

Table 4. Effect of poly(γ-glutamic acid) on diversity of soil bacteria and fungi at late seedling stage and blooming stage.

	Bacteria				Fungi
	Late seedling stage		Blooming stage		Late seedling stage		Blooming stage
Treatment	Band number	Shannon index	Band number	Shannon index	Band number	Shannon index	Band number	Shannon index
T1	15	2.32	19	2.54	20	2.52	11	2.02
T2	14	2.28	18	2.44	21	2.58	10	2.00
T3	13	2.18	19	2.63	22	2.65	12	2.03
T4	24	2.73	27	2.92	27	2.68	20	2.12
T5	24	2.58	29	3.12	29	2.75	21	2.10
T6	25	2.67	28	3.01	29	2.79	22	2.15
T7	27	2.77	29	3.13	32	2.75	22	2.35

Figure 3. Effects of poly(γ-glutamic acid) (γ-PGA) on the ammonium nitrogen (-N) in potted soil. These values are expressed as mean ± SD (n = 3). Statistical analysis was performed by Duncan's test (P < 0.05). Means in the same column with different letters are statistically different. T₁, a check without urea; T₂, a check with urea only; T₃, urea mixed with 3 mg of glutamic acid per kilogram of soil; T₄, urea mixed with 3 mg of γ-PGA per kilogram of soil; T₅, urea mixed with 10 mg of γ-PGA per kilogram of soil; T₆, urea coated with γ-PGA (0.9%, m/m); and T₇, urea coated with γ-PGA (3.1%, m/m).

Figure 4. Effects of poly(γ-glutamic acid) (γ-PGA) on the nitrate nitrogen (-N) in potted soil. These values are expressed as mean ± SD (n = 3). Statistical analysis was performed by Duncan's test (P < 0.05). Means in the same column with different letters are statistically different. T₁, a check without urea; T₂, a check with urea only; T₃, urea mixed with 3 mg of glutamic acid per kilogram of soil; T₄, urea mixed with 3 mg of γ-PGA per kilogram of soil; T₅, urea mixed with 10 mg of γ-PGA per kilogram of soil; T₆, urea coated with γ-PGA (0.9%, m/m); and T₇, urea coated with γ-PGA (3.1%, m/m).

Figure 5. Effects of poly(γ-glutamic acid) (γ-PGA) on the SMBN in potted soil. These values are expressed as mean ± SD (n = 3). Statistical analysis was performed by Duncan's test (P < 0.05). Means in the same column with different letters are statistically different. T₁, a check without urea; T₂, a check with urea only; T₃, urea mixed with 3 mg of glutamic acid per kilogram of soil; T₄, urea mixed with 3 mg of γ-PGA per kilogram of soil; T₅, urea mixed with 10 mg of γ-PGA per kilogram of soil; T₆, urea coated with γ-PGA (0.9%, m/m); and T₇, urea coated with γ-PGA (3.1%, m/m).

Figure 6. Effects of poly(γ-glutamic acid) (γ-PGA) on the fixed -N in potted soil. These values are expressed as mean ± SD (n = 3). Statistical analysis was performed by Duncan's test (P < 0.05). Means in the same column with different letters are statistically different. T₁, a check without urea; T₂, a check with urea only; T₃, urea mixed with 3 mg of glutamic acid per kilogram of soil; T₄, urea mixed with 3 mg of γ-PGA per kilogram of soil; T₅, urea mixed with 10 mg of γ-PGA per kilogram of soil; T₆, urea coated with γ-PGA (0.9%, m/m); and T₇, urea coated with γ-PGA (3.1%, m/m).

Figure 7. Effects of poly(γ-glutamic acid) (γ-PGA) on the urease activity in potted soil. These values are expressed as mean ± SD (n = 3). Statistical analysis was performed by Duncan's test (P < 0.05). Means in the same column with different letters are statistically different. T₁, a check without urea; T₂, a check with urea only; T₃, urea mixed with 3 mg of glutamic acid per kilogram of soil; T₄, urea mixed with 3 mg of γ-PGA per kilogram of soil; T₅, urea mixed with 10 mg of γ-PGA per kilogram of soil; T₆, urea coated with γ-PGA (0.9%, m/m); and T₇, urea coated with γ-PGA (3.1%, m/m).

Figure 8. Relationships between different forms of N in pot rapeseed soil. Green filled circles, strongly fixed ; red filled circles, weakly fixed or exchangeable ; blue filled circles, .