Precipitation regulates the response of salinized grassland net primary productivity to nitrogen addition and mowing in the agro-pastoral zone

doi:10.17521/cjpe.2024.0030

Abstract

Abstract:

Aims In the salinized grassland of the agro-pastoral ecotone with limited nutrients, the increase of nitrogen input induced by agricultural fertilization and the change of land use patterns usually causes changes in soil available nutrients, which could further affect the net primary productivity of plants. However, due to the impact of annual precipitation, it is still uncertainty about whether the response of net primary productivity of plants to nitrogen addition and mowing varies with changes in rainfall.

Methods This study investigated plant net primary productivity under nitrogen addition and mowing at salinized grassland in the agro-pastoral ecotone of northern China, based on the experimental platform for nitrogen forms and mowing at the National Research Station of Grassland Ecosystems on the Loess Plateau in Youyu, Shanxi Province. There were six treatments including control and simulated nitrogen deposition experiments with two common nitrogen compounds (ammonium nitrate and urea), combined with and without mowing.

Important findings The results showed that: (1) Regardless of mowing or un-mowing treatments, short-term addition of ammonium nitrate and urea significantly increased the content of inorganic nitrogen in the soil, thereby increasing the aboveground (ANPP), belowground (BNPP), and total net primary productivity (NPP); (2) ANPP, BNPP, NPP, inorganic nitrogen content, and soil water content showed significant interannual differences, with higher values observed in the wet year (2018) than in the dry year (2017); (3) The interaction between short-term nitrogen addition and year had a significant impact on NPP. In the wet year, the positive effect of nitrogen addition on NPP was significantly higher than that in the dry year, which was mainly related to the synergistic effect of soil nitrogen and water; (4) Mowing decreased NPP and had a significant interactive effect with the year on the BNPP:ANPP. In the dry year, mowing generally decreased BNPP:ANPP. However, in the wet year, this negative effect gradually weakened and even turned into a positive effect. These results highlighted the crucial role of natural precipitation in regulating the response of net primary productivity of salinized grassland in the agro-pastoral ecotone to anthropogenic disturbances, and further indicated that the salinized grassland ecosystem in the agro-pastoral ecotone is jointly limited by nitrogen and water.

Key words: agro-pastoral ecotone, salinized, precipitation, mowing, nitrogen addition, net primary productivity

HAO Jie, DIAO Hua-Jie, SU Yuan, WU Shuai-Kai, GAO Yang-Yang, LIANG Wen-Jun, NIU Hui-Min, YANG Qian-Wen, CHANG Jie, WANG Ge, XU Wen-Li, MA Teng-Fei, DONG Kuan-Hu, $\boxed{\hbox{WANG Chang-Hui}}$. Precipitation regulates the response of salinized grassland net primary productivity to nitrogen addition and mowing in the agro-pastoral zone[J]. Chin J Plant Ecol, 2025, 49(5): 710-719.

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Figures/Tables 7

Fig. 1 Daily average air temperature (A) and accumulated precipitation (B) in the growing season (May-September) of salinized grassland at 2017 and 2018.

Table 1 Repeated analysis of variance of the effects of nitrogen addition and mowing on soil inorganic nitrogen (IN) content and soil water content (SM) in agro-pastoral ecotone

影响因子 Effecting factor	无机氮含量 IN content		土壤含水量 SM
影响因子 Effecting factor	F	p	F	p
截距 Intercept	467.78	<0.01	189.17	<0.01
氮添加 Nitrogen addition (N)	3.57^*	<0.05	0.85	0.43
刈割 Mowing (M)	0.04	0.83	0.57	0.45
年 Year (Y)	251.19^**	<0.01	37.91^**	<0.01
N × M	0.01	0.98	0.30	0.73
N × Y	2.84^#	0.06	0.24	0.78
M × Y	0.75	0.38	7.12^*	<0.05
N × M × Y	0.00	0.99	0.00	0.99

Fig. 2 Effects of nitrogen addition (N) and mowing (M) on soil inorganic nitrogen (IN, A) content, soil water content (SM, C) and inter-annual average values (B, D) in agro-pastoral ecotone. AN+M, NH4NO3 + mowing; AN+UM, NH4NO3 + un-mowing; CK+M, control + mowing; CK+UM, control + un-mowing; UN+M, urea + mowing; UN+UM, urea + un-mowing. Different lowercase letters indicate significant difference in indicators among different N treatments at p < 0.05 under the un-mowing and the mowing treatment, and different uppercase letters represent significant differences between years among different treatments (p < 0.05). Results (F values) of linear mixed-effects models are shown in figure and indicated by * when p < 0.05, and ns when not statistically significant (p > 0.1).

Table 2 Repeated analysis of variance of the effects of nitrogen addition and mowing on aboveground (ANPP), belowground (BNPP), total net primary productivity (NPP) and BNPP:ANPP in agro-pastoral ecotone

影响因子 Effecting factor	地上净初级生产力 ANPP		地下净初级生产力 BNPP		总初级生产力 NPP		地下:地上净初级生产力 BNPP:ANPP
影响因子 Effecting factor	F	p	F	p	F	p	F	p
截距 Intercept	234.28	<0.01	156.63	<0.01	230.27	<0.01	149.60	<0.01
氮添加 Nitrogen addition (N)	14.81^**	<0.01	4.08^*	<0.05	10.56^**	<0.01	1.86	0.16
刈割 Mowing (M)	0.93	0.33	2.75	0.10	4.09^*	<0.05	0.91	0.34
年 Year (Y)	11.33^**	<0.01	4.21^*	<0.05	11.06^**	<0.01	0.00	0.92
N × M	0.22	0.80	1.04	0.35	1.14	0.32	1.20	0.30
N × Y	3.80^*	<0.05	0.86	0.42	2.77^#	0.07	0.14	0.86
M × Y	0.50	0.48	1.39	0.24	0.82	0.36	3.13^#	0.08
N × M × Y	0.01	0.98	0.09	0.90	0.07	0.93	0.67	0.51

Fig. 3 Effects of nitrogen addition (N) and mowing (M) on the aboveground (ANPP, A), belowground (BNPP, C), and total net primary productivity (NPP, E), as well as the belowground/aboveground net primary productivity ratio (G), and the inter-annual means (B, D, F, H). AN+M, NH4NO3 + mowing; AN+UM, NH4NO3 + un-mowing; CK+M, control + mowing; CK+UM, control + un-mowing; UN + M, urea + mowing; UN+UM, urea + un-mowing. Different lowercase letters indicate significant difference in indicators among different nitrogen treatments at p < 0.05 under the un-mowing and the mowing treatment, and different uppercase letters represent significant differences between years among different treatments (p < 0.05). Results (F values) of linear mixed-effects models are shown in figure and indicated by ** when p < 0.01, * when 0.01 ≤ p < 0.05, # when 0.05 ≤ p < 0.10, and ns when p > 0.10.

Fig. 4 Relationship between total net primary productivity and soil inorganic nitrogen content (A), soil water content (B), soil temperature (C), and the relationship between soil inorganic nitrogen content and soil water content (D) under mowing and un-mowing treatment measured in 2017 and 2018 in the salinized grasslands of the agro-pastoral ecotone. Different colored squares represent different forms of nitrogen addition treatments. Solid lines and dotted lines represent un-mowing and mowing treatments, respectively. Shadow parts represent 95% confidence intervals. AN+M, NH4NO3 + mowing; AN+UM, NH4NO3 + un-mowing; CK+M, control + mowing; CK+UM, control + un-mowing; UN+M, urea + mowing; UN+UM, urea + un-mowing.

Fig. 5 Variability of total net primary productivity (NPP) across the sampling dates in the context of soil inorganic nitrogen content, and soil water content in the salinized grasslands of the agro-pastoral ecotone.

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