Response of soil microbial community and diversity to increasing water salinity and nitrogen fertilization rate in an arid soil

Figures & data

Table 1. Chemical characteristic of the three types of irrigation water in this study.

Irrigation water	pH	SAR	Ion concentration (meq L^−1)
			K^+	Na^+	Ca^2+	Mg^2+	HCO3^−	Cl^−	SO4^2−
FW	7.52	0.16	0.33	0.22	2.44	1.18	0.98	2.46	0.73
BW	7.18	6.74	0.33	25.52	27.50	1.18	1.07	52.57	0.83
SW	7.09	8.91	0.33	43.04	45.50	1.18	1.15	88.00	0.83

Note: The symbols FW, BW, and SW represent irrigation water with EC of 0.35, 4.61, and 8.04 dS m⁻¹, respectively.

Table 2. Soil chemical properties as affected by irrigation water salinity and N fertilization.

N Rate	Water salinity	Soil water content	EC	pH	OM	Total N	NO3^−–N	NH4^+–N
		(%)	(dS m^−1)		(g kg^−1)	(g kg^−1)	(mg kg^−1)	(mg kg^−1)
N0	FW	16.81 b	0.27 c	8.00 a	16.36 bc	0.66 bc	10.51 d	5.13 e
	BW	17.69 a	0.86 b	7.82 b	15.70 cd	0.65 cd	9.26 de	6.55 d
	SW	18.07 a	1.16 a	7.78 bc	15.12 d	0.62 d	7.62 e	7.90 c
N360	FW	15.60 c	0.33 c	7.96 a	17.83 a	0.74 a	47.64 a	7.85 c
	BW	16.68 b	0.90 b	7.76 bc	17.21 ab	0.70 b	29.20 b	11.91 b
	SW	17.54 a	1.22 a	7.75 c	16.97 ab	0.65 cd	22.50 c	13.33 a
Two-way ANOVA (significance)
Water salinity (S)		***	***	***	**	***	***	***
Nitrogen rate (N)		***	**	**	***	***	***	***
Interaction (S × N)		ns	ns	ns	ns	*	***	***

Note: Different letters within the same column indicate significant differences at P < 0.05 level among the six treatments. The symbols FW, BW, and SW represent irrigation water with EC of 0.35, 4.61, and 8.04 dS m⁻¹, respectively. The symbols N0 and N360 represent 0 and 360 kg N ha⁻¹, respectively.

***p < 0.001.

**p < 0.01.

*p < 0.05.

ns, p ≥ 0.05.

Table 3. Soil microbial biomass C (MBC), microbial biomass N (MBN), and basal respiration as affected by irrigation water salinity and N fertilization.

N rate	Water salinity	MBC	MBN	MBC/MBN	Basal respiration
		(mg kg^−1)	(mg kg^−1)		(mg CO2 g^−1d^−1)
N0	FW	165.6 b	26.99 c	6.15 c	307.8 c
	BW	129.7 c	20.05 d	6.51 c	228.9 d
	SW	86.4 d	9.13 e	9.48 a	202.8 e
N360	FW	222.8 a	63.11 a	3.54 d	391.8 a
	BW	180.4 b	34.60 b	5.24 c	367.9 b
	SW	160.8 b	20.15 d	7.98 b	301.4 c
Two-way ANOVA (significance)
Water salinity (S)		***	***	***	***
Nitrogen rate (N)		***	***	***	***
Interaction (S × N)		ns	***	ns	***

Note: Different letters within the same column indicate significant differences at P < 0.05 level among the six treatments. The symbols FW, BW, and SW represent irrigation water with EC of 0.35, 4.61, and 8.04 dS m⁻¹, respectively. The symbols N0 and N360 represent 0 and 360 kg N ha⁻¹, respectively.

***p < 0.001.

**p < 0.01.

*p < 0.05.

ns, p ≥ 0.05.

Table 4. Relative abundances of microbial groups based on PLFA (ug kg⁻¹) analysis as affected by irrigation water salinity and N fertilization

N rate	Water salinity	Total PLFA	Bacterial PLFA	G^+ bacterial PLFA	G^− bacteria PLFA	Fungal PLFA	Fungal/bacterial
N0	FW	7.73 b	5.65 b	1.17 a	4.61 c	0.31 a	0.06 a
	BW	6.02 c	5.04 c	0.29 f	4.70 c	0.23 b	0.05 b
	SW	4.36 d	3.38 d	0.40 e	2.88 d	0.14 d	0.04 b
N360	FW	8.76 a	6.36 a	0.48 d	5.66 a	0.17 c	0.03 c
	BW	7.11 b	5.84 b	0.63 b	5.22 b	0.14 d	0.02 cd
	SW	8.01 ab	6.18 a	0.52 c	5.18 b	0.12 d	0.02 d
Two-way ANOVA (significance)
Water salinity (S)		***	***	***	***	***	***
Nitrogen rate (N)		***	***	***	***	***	***
Interaction (S × N)		***	***	***	***	***	ns

Note: Different letters within the same column indicate significant differences at P < 0.05 level among the six treatments. The symbols FW, BW, and SW represent irrigation water with EC of 0.35, 4.61, and 8.04 dS m⁻¹, respectively. The symbols N0 and N360 represent 0 and 360 kg N ha⁻¹, respectively.

***p < 0.001.

**p < 0.01.

*p < 0.05.

ns, p ≥ 0.05.

Figure 1. PCA of PLFA profiles as affected by irrigation water salinity and N fertilization. PC1 described 94.3% and PC2 5.0% of variation in the data. Abbreviations: FWN0 stand for water salinity of 0.35 dS m⁻¹ with unfertilized treatment; FWN360 stand for water salinity of 0.35 dS m⁻¹ with fertilized treatment; BWN0 stand for water salinity of 4.61 dS m⁻¹ with unfertilized treatment; BWN360 stand for water salinity of 4.61 dS m⁻¹ with fertilized treatment; SWN0 stand for water salinity of 8.04 dS m⁻¹ with unfertilized treatment; SWN360 stand for water salinity of 8.04 dS m⁻¹ with fertilized treatment. Each symbol represents the average score of three replicates.

Figure 2. AWCD during 120-h incubations. Values are the mean of three replicates. Error bars represent standard deviations. The symbols FW, BW, and SW represent irrigation water with EC of 0.35, 4.61, and 8.04 dS m⁻¹, respectively. The symbols N0 and N360 represent the 0 and 360 kg N ha⁻¹ treatments, respectively.

Figure 3. Carbon utilization profiles (72 h) as affected by irrigation water salinity and N fertilization. The symbols FW, BW, and SW represent irrigation water with EC of 0.35, 4.61, and 8.04 dS m⁻¹, respectively. The symbols N0 and N360 represent the 0 and 360 kg N ha⁻¹ treatments, respectively. Additional abbreviations: CH, carbohydrates; AM, amines; AA, amino acids; PM, polymers; CA, carboxylic acid; and PA, phenolic acid.

Figure 4. PCA of carbon utilization profiles (72 h) as affected by irrigation water salinity and N fertilization. PC1 described 76.9% and PC2 14.8% of variation in the data. Abbreviations: FWN0 stand for water salinity of 0.35 dS m⁻¹ with unfertilized treatment; FWN360 stand for water salinity of 0.35 dS m⁻¹ with fertilized treatment; BWN0 stand for water salinity of 4.61 dS m⁻¹ with unfertilized treatment; BWN360 stand for water salinity of 4.61 dS m⁻¹ with fertilized treatment; SWN0 stand for water salinity of 8.04 dS m⁻¹ with unfertilized treatment; SWN360 stand for water salinity of 8.04 dS m⁻¹ with fertilized treatment. Each symbol represents the average score of three replicates.

Table 5. Diversity indices of microbial C source utilization as affected by irrigation water salinity and N fertilization.

N rate	Water salinity	Diversity index
		R (richness)	H’ (Shannon)	E (Shannon)	D (Simpson)
N0	FW	29 a	2.89 a	0.86 a	1.05 b
	BW	29 a	2.96 a	0.88 a	1.02 c
	SW	26 b	2.56 b	0.79 b	1.16 a
N360	FW	29 a	2.99 a	0.89 a	1.02 c
	BW	27 ab	2.83 a	0.86 a	1.04 bc
	SW	26 b	2.93 a	0.89 a	1.03 bc
Two-way ANOVA (significance)
Water salinity (S)		***	***	ns	***
Nitrogen rate (N)		Ns	**	***	***
Interaction (S × N)		Ns	***	***	***

Note: Different letters within the same column indicate significant differences at P < 0.05 level among the six treatments. The symbols FW, BW, and SW represent irrigation water with EC of 0.35, 4.61, and 8.04 dS m⁻¹, respectively. The symbols N0 and N360 represent 0 and 360 kg N ha⁻¹, respectively.

***p < 0.001.

**p < 0.01.

*p < 0.05.

ns, p ≥ 0.05.