Defense strategies of dominant plants under different grazing intensity in the typical temperate steppe of Nei Mongol, China

doi:10.17521/cjpe.2019.0329

Abstract

Abstract:

Aims Grazing is one of the main grassland using modes, which has caused certain biotic stress on pasture. In order to survive, pasture initiates defense mechanisms by regulating the primary and secondary metabolic processes. This article aims to 1) figure out the distribution of defensive substances in different organs produced by the dominant plants Stipa grandis and Leymus chinensis; 2) explore the similarities and differences of the defense mechanisms and carbon-nitrogen trade-off strategies in S. grandis and L. chinensis.
Methods We conducted a different grazing intensity experiment in the typical temperate steppe of Nei Mongol. The lignin and secondary metabolites, such as tannins, flavonoids, phenols and alkaloids, as well as the ratio of carbon and nitrogen in different organs of the dominant plants S. grandis and L. chinensis were investigated.
Important findings Our results showed that S. grandis and L. chinensis produced a large number of secondary metabolites such as tannins, flavonoids, phenols and alkaloids in the face of grazing stress. The leaves were the main synthesis and storage organs. In addition, the chemical defense mechanism of L. chinensis was well induced and expressed under moderate grazing. There was no significant increase in the lignin content in the aboveground parts of S. grandis and L. chinensis. Therefore, both of them were more inclined to chemical defense than mechanical defense in the mechanism of avoiding grazing. Because of the higher nitrogen use efficiency of L. chinensis, it could be protected by both carbon and nitrogen metabolic pathways. However, Stipa grandis did not efficiently distribute nitrogen into chemical defense in the early stages of growth. More resources still used for primary metabolism in the early stage of S. grandis and L. chinensis growth, under light grazing stress, which increased their grazing resistance. Therefore, light grazing is conducive to improving the carbon and nitrogen use efficiency of pasture, and improving ecosystem productivity and stability.

Key words: secondary metabolism, defense mechanism, carbon-nitrogen trade-off, dominant species, grazing intensity, Stipa grandis, Leymus chinensis

LI Ying, GONG Ji-Rui, LIU Min, HOU Xiang-Yang, DING Yong, YANG Bo, ZHANG Zi-He, WANG Biao, ZHU Chen-Chen. Defense strategies of dominant plants under different grazing intensity in the typical temperate steppe of Nei Mongol, China[J]. Chin J Plant Ecol, 2020, 44(6): 642-653.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2019.0329

https://www.plant-ecology.com/EN/Y2020/V44/I6/642

Figures/Tables 8

Fig. 1 Monthly precipitation and mean air temperature at the study sites in the typical temperate steppe of Nei Mongol in 2016.

Fig. 2 Lignin content of Stipa grandis and Leymus chinensis in the typical temperate steppe of Nei Mongol in June (A, B) and August (C, D) under different grazing levels (mean ± SE). CK, grazing exclusion; LG, light grazing; MG, moderate grazing; HG, heavy grazing; EHG, extremely heavy grazing. Different lowercase letters indicate significant differences among treatments (p < 0.05).

Fig. 3 Tannins content of Stipa grandis and Leymus chinensis in the typical temperate steppe of Nei Mongol in June (A, B) and August (C, D) under different grazing levels (mean ± SE). CK, grazing exclusion; LG, light grazing; MG, moderate grazing; HG, heavy grazing; EHG, extremely heavy grazing. Different lowercase letters indicate significant differences among treatments (p < 0.05).

Fig. 4 Total flavonoids contents of Stipa grandis and Leymus chinensis in the typical temperate steppe of Nei Mongol in June (A, B) and August (C, D) under different grazing levels (mean ± SE). CK, grazing exclusion; LG, light grazing; MG, moderate grazing; HG, heavy grazing; EHG, extremely heavy grazing. Different lowercase letters indicate significant differences among treatments (p < 0.05).

Fig. 5 Total phenols contents of Stipa grandis and Leymus chinensis in the typical temperate steppe of Nei Mongol in June (A, B) and August (C, D) under different grazing levels (mean ± SE). CK, grazing exclusion; LG, light grazing; MG, moderate grazing; HG, heavy grazing; EHG, extremely heavy grazing. Different lowercase letters indicate significant differences among treatments (p < 0.05).

Fig. 6 Alkaloid contents of Stipa grandis and Leymus chinensis in the typical temperate steppe of Nei Mongol in June and August under different grazing levels (mean ± SE). CK, grazing exclusion; LG, light grazing; MG, moderate grazing; HG, heavy grazing; EHG, extremely heavy grazing. Different lowercase letters indicate significant differences among treatments (p < 0.05).

Fig. 7 The C:N in leafs of Stipa grandis and Leymus chinensis in the typical temperate steppe of Nei Mongol in June (A, B) and August (C, D) under different grazing levels (mean ± SE). CK, grazing exclusion; LG, light grazing; MG, moderate grazing; HG, heavy grazing; EHG, extremely heavy grazing. Different lowercase letters indicate significant differences among treatments (p < 0.05).

Table 1 Correlation analysis of defense metabolites and C:N in leaves of Stipa grandis and Leymus chinensis in the typical temperate steppe of Nei Mongol in June and August

		大针茅 S. grandis						羊草 L. chinensis
		单宁 Tannins	总黄酮 Flavonoids	总酚 Phenols	木质素 Lignin	总生物碱 Alkaloid	碳氮比 C:N	单宁 Tannins	总黄酮 Flavonoids	总酚 Phenols	木质素 Lignin	总生物碱 Alkaloid	碳氮比 C:N
大针茅 S. grandis	单宁 Tannins		0.800	0.900^*	-0.400	0.051	-0.300		0.400	0.400	-0.800	0.600	0.000
	总黄酮 Flavonoids			0.900^*	0.100	0.154	0.200			1.000^**	-0.200	-0.400	0.800
	总酚 Phenols				-0.300	0.051	-0.100				-0.200	-0.400	0.800
	木质素 Lignin					-0.154	0.500					-0.800	0.400
	总生物碱 Alkaloid						0.718						-0.800
	碳氮比 C:N
羊草 L. chinensis	单宁 Tannins		0.900^*	0.300	-0.200	0.600	0.500		0.000	0.600	-1.000^**	0.400	-0.600
	总黄酮 Flavonoids			0.600	-0.100	0.700	0.700			0.800	0.000	-0.800	-0.800
	总酚 Phenols				0.300	0.500	0.900^*				-0.600	-0.400	-1.000^**
	木质素 Lignin					0.600	-0.100					-0.400	0.600
	总生物碱 Alkaloid						0.300						0.400
	碳氮比 C:N

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