Effects of nitrogen addition at different levels on soil microorganisms in saline-alkaline grassland of northern China

doi:10.17521/cjpe.2021.0072

Abstract

Abstract:

Aims Nitrogen (N) availability is an important limiting factor for grassland ecosystem productivity, and soil microorganisms are the main driving factor on soil N transformation. With the increase of atmospheric N deposition, the response of soil microbial characteristics to different nitrogen input levels is still unclear especially in saline-alkaline grassland.

Methods The experiment was conducted in Youyu Loess Plateau Grassland Ecosystem Research Station, Shanxi Province. Eight different nitrogen addition levels were set, which were 0, 1, 2, 4, 8, 16, 24 and 32 g·m^-2·a^-1, respectively. The Ammonia-oxidizing microorganisms (i.e. ammonia-oxidizing bacteria (AOB) and ammonia- oxidizing archaea (AOA)) abundance, soil bacterial and fungal abundance, as well as soil microbial biomass carbon (MBC) and nitrogen (MBN) content were measured in the growing season (May to September) in 2020 to explore the effects of different levels of N addition on soil microbial characteristics.

Important findings Our results showed that: (1) Sampling month had a significant effect on soil AOB, bacteria, fungal abundance and MBC, MBN content due to the variation in soil temperature and soil water content in the growing season. (2) N addition had a significant effect on soil AOB abundance, while had no effects on soil MBC, MBN content, and bacterial and fungal composition. (3) Higher N addition (24 and 32 g·m^-2·a^-1) significantly increased the abundance of ammonia-oxidizing bacteria (AOB) on the early growth stage (May to August), while having no effect on late growth period (September). (4) Soil microorganisms were mainly regulated by soil cations concentrations and soil pH values, which explained the variation of soil microorganisms by 21.8% and 17.2%, respectively. We found that soil microorganisms were not sensitive to N addition in saline-alkaline grassland, while AOB showed a significant increase under higher N addition, indicating that higher N addition might promote soil N transformation.

Key words: saline alkaline grassland, nitrogen addition, Ammonia-oxidizing microorganisms, bacteria, fungi

YANG Jian-Qiang, DIAO Hua-Jie, HU Shu-Ya, WANG Chang-Hui. Effects of nitrogen addition at different levels on soil microorganisms in saline-alkaline grassland of northern China[J]. Chin J Plant Ecol, 2021, 45(7): 780-789.

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https://www.plant-ecology.com/EN/Y2021/V45/I7/780

Figures/Tables 7

Table 1 Effects of nitrogen (N) levels, month and their interactions on soil microorganism (AOA, AOB, bacteria, fungi abundance and MBC, MBN content) in saline-alkaline grassland

处理 Treatment	氨氧化古菌 AOA		氨氧化细菌 AOB		细菌 Bacteria		真菌 Fungal		微生物生物量碳 MBC		微生物生物量氮 MBN
处理 Treatment	F	p	F	p	F	p	F	p	F	p	F	p
氮水平 N levels	0.38	0.907	6.72	<0.000 1	0.65	0.710	0.92	0.498	1.62	0.159	1.02	0.434
采样月份 Sampling month	9.72	<0.000 1	1.21	0.309	58.66	<0.000 1	24.05	<0.000 1	6.21	<0.000 1	8.54	<0.000 1
月份×氮水平 Month × N levels	0.83	0.712	2.44	<0.000 1	0.62	0.930	1.09	0.357	0.78	0.776	0.58	0.951

Fig. 1 Seasonal and inter-annual mean values (mean ± SE) of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) abundance in saline-alkaline grassland. *, ** and *** represent the differences are significant with p < 0.05, p < 0.01 and p < 0.000 1, respectively; different lowercase letters in the bar chart indicate significant differences among treatments (p < 0.05). CK, control; N1, nitrogen addition level 1 g·m-2·a-1; N2, nitrogen addition level 2 g·m-2·a-1; N4, nitrogen addition level 4 g·m-2·a-1; N8, nitrogen addition level 8 g·m-2·a-1; N16, nitrogen addition level 16 g·m-2·a-1; N24, nitrogen addition level 24 g·m-2·a-1; N32, nitrogen addition level 32 g·m-2·a-1.

Fig. 2 Seasonal and inter-annual mean values (mean ± SE) of soil bacterial and fungal in saline-alkaline grassland. *, ** and *** represent the differences among treatments are significant with p < 0.05, p < 0.01 and p < 0.000 1, respectively; different lowercase letters in the bar chart indicate significant differences among treatments (p < 0.05). CK, control; N1, nitrogen addition level 1 g·m-2·a-1; N2, nitrogen addition level 2 g·m-2·a-1; N4, nitrogen addition level 4 g·m-2·a-1; N8, nitrogen addition level 8 g·m-2·a-1; N16, nitrogen addition level 16 g·m-2·a-1; N24, nitrogen addition level 24 g·m-2·a-1; N32, nitrogen addition level 32 g·m-2·a-1.

Fig. 3 Seasonal and inter-annual mean values (mean ± SE) of soil microbial biomass carbon (MBC) and nitrogen (MBN) content in saline-alkaline grassland. *, ** and *** represent the differences among treatments are significant with p < 0.05, p < 0.01 and p < 0.000 1, respectively; different lowercase letters in the bar chart indicate significant differences among treatments (p < 0.05). CK, control; N1, nitrogen addition level 1 g·m-2·a-1; N2, nitrogen addition level 2 g·m-2·a-1; N4, nitrogen addition level 4 g·m-2·a-1; N8, nitrogen addition level 8 g·m-2·a-1; N16, nitrogen addition level 16 g·m-2·a-1; N24, nitrogen addition level 24 g·m-2·a-1; N32, nitrogen addition level 32 g·m-2·a-1.

Table 2 Pearson correlation between soil microorganisms and soil microenvironment, soil cations and anions concentration

因子 Factor	AOA	AOB	Bacteria	Fungi	MBC	MBN	ST	SM	pH	Ca²⁺	K⁺	Mg²⁺	Na⁺	STC	CO₃^2-	HCO₃^-	Cl^-	STA	NH₄⁺
AOB	0.23
细菌 Bacteria	-0.49^**	-0.03
真菌 Fungi	0.47^**	0.09	-0.06
MBC	-0.19	-0.01	0.33^*	0.11
MBN	0.09	0.14	0.19	0.23	0.44^**
ST	-0.26	-0.61^**	-0.06	-0.19	-0.21	-0.47^**
SM	-0.26	-00.19	0.03	-0.17	0.24	0.37^**	0.00
pH	-0.36^*	-0.63^**	0.10	-0.10	0.14	-0.07	0.53^**	0.42^**
Ca²⁺	0.42^**	0.58^**	-0.28	0.21	-0.29^*	-0.05	-0.37^**	-0.34^*	-0.61^**
K⁺	0.04	-0.03	0.01	0.02	-0.02	-0.08	0.22	-0.17	0.10	-0.02
Mg²⁺	0.42^**	-0.32^*	-0.36^*	0.06	0.01	-0.01	0.29^*	0.23	0.34^*	-0.36^*	0.17
Na⁺	-0.47^**	-0.46^**	0.07	-0.29^*	0.15	0.05	0.25	0.62^**	0.77^**	-0.51^**	-0.09	0.17
STC	0.52^**	-0.11	-0.50^**	0.09	-0.13	-0.03	0.17	0.21	0.24	0.09	0.27	0.85^**	0.19
CO₃^2-	-0.45^**	-0.27	0.28	-0.21	0.08	-0.11	0.23	0.21	0.39^**	-0.26	-0.20	-0.24	0.34^*	-0.31^*
HCO₃^-	0.25	0.05	-0.27	-0.13	-0.10	0.02	0.08	0.16	0.14	0.11	0.39^**	0.39^**	0.22	0.59^**	-0.47^**
Cl^-	0.06	-0.06	0.03	-0.26	-0.07	0.01	0.01	0.03	0.03	0.14	0.12	0.09	0.06	0.22	-0.03	0.21
STA	0.19	0.00	-0.24	-0.19	-0.10	0.00	0.13	0.21	0.22	0.08	0.39^**	0.38^**	0.29^*	0.59^**	-0.33^*	0.98^**	0.30^*
NH₄⁺	0.26	0.05	-0.12	0.32^*	-0.20	-0.17	-0.19	-0.21	-0.15	0.33^*	-0.09	-0.19	-0.29^*	-0.10	-0.33^*	0.08	-0.19	0.01
NO₃^-	-0.09	-0.11	0.17	0.05	0.37^**	-0.02	-0.18	-0.04	-0.03	-0.02	-0.03	-0.11	0.08	-0.09	-0.16	0.03	-0.03	0.00	0.22

Fig. 4 Effects of nitrogen (N) addition at different levels on soil pH value (mean ± SE), cations, and anions concentration. CK, control; N1, nitrogen addition level 1 g·m-2·a-1; N2, nitrogen addition level 2 g·m-2·a-1; N4, nitrogen addition level 4 g·m-2·a-1; N8, nitrogen addition level 8 g·m-2·a-1; N16, nitrogen addition level 16 g·m-2·a-1; N24, nitrogen addition level 24 g·m-2·a-1; N32, nitrogen addition level 32 g·m-2·a-1.

Fig. 5 Redundancy analysis (RDA) of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), bacteria, fungi abundance and microbial biomass carbon (MBC), and nitrogen (MBN) content with related factors. SM, soil moisture; ST, soil temperature; STA, soil total anions content; STC, soil total cations content.

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