Effects of different herbivore assemblage on relationship between Kobresia humilis seed size and seed number in an alpine grassland

doi:10.17521/cjpe.2022.0134

Abstract

Abstract:

Aims Seed size and number variation is the core issue in the study of plant fitness. Exploring the grazing effects of different large herbivore assemblage on the relationship between seed size and number of dominant species in Kobresia grasslands, is helpful to understand the reproductive strategy and population regeneration mechanism.

Methods This research was conducted on the technical platform of adaptive management of alpine grassland- livestock system on the Qingzang Plateau. There were six grazing treatments: no grazing (control), single yak grazing, single Xizang sheep grazing, yak:Xizang sheep grazing ratios of 1:2, 1:4 and 1:6. And we analyzed the reproductive characteristics of K. humilis, the relationship between seed size, seed number and its tradeoff.

Important findings The results showed that: 1) Grazing treatment increased the seed size and seed number of K. humilis by more than 15% and 30%, respectively. The variation coefficient of seed size decreased by at least 15% under other grazing treatments except for yak:Xizang grazing ratio of 1:2. While the variation coefficient of seed number decreased by more than 25%. 2) Pearson correlation analysis showed that there were positive correlation between seed size, seed number and reproductive traits under grazing treatments. 3) Grazing treatments increased the tradeoff between seed size and seed number which was largely affected by the mass of single reproductive branch. The results suggest that even at moderate grazing, livestocks are still the limiting factors for the acquisition of resources. Long-term grazing changes the potential relationship and tradeoff among the traits of K. humilis, stabilizes the features of seed size and seed number. The reproductive strategy of K. humilis is optimized by increasing seed size and seed number, which improves the near-ground competitiveness and fitness of offsprings.

Key words: alpine grassland, Kobresia humilis, moderate grazing, herbivore grazing assemblage, seed size, seed number

DONG Quan-Min, ZHAO Xin-Quan, LIU Yu-Zhen, FENG Bin, YU Yang, YANG Xiao-Xia, ZHANG Chun-Ping, CAO Quan, LIU Wen-Ting. Effects of different herbivore assemblage on relationship between Kobresia humilis seed size and seed number in an alpine grassland[J]. Chin J Plant Ecol, 2022, 46(9): 1018-1026.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0134

https://www.plant-ecology.com/EN/Y2022/V46/I9/1018

Figures/Tables 8

Fig. 1 Picture of reproductive individual of Kobresia humilis.

Fig. 2 Plots diagram and area of grazing experiments. CK, no grazing; M1, M2 and M3 representing yak and Xizang sheep grazing ratios with 1:2, 1:4 and 1:6; S, single Xizang sheep grazing; Y, single yak grazing.

Fig. 3 Trade-off relationship pattern diagram between seed size and seed number.

Fig. 4 Effects of herbivore grazing assemblage on the seed size (A) and seed number (B) of Kobresia humilis in an alpine grassland (mean ± SE). CK, no grazing; M1, M2 and M3 representing yak and Xizang sheep grazing ratios with 1:2, 1:4 and 1:6; S, single Xizang sheep grazing; Y, single yak grazing. Different lowercase letters indicate significant difference among different grazing treatments (p < 0.05).

Fig. 5 Coefficient variation of seed size (A) and seed number (B) of Kobresia humilis in alpine grassland. CK, no grazing; M1, M2 and M3 representing yak and Xizang sheep grazing ratios with 1:2, 1:4 and 1:6; S, single Xizang sheep grazing; Y, single yak grazing.

Table 1 Pearson correlation between seed size, seed number and reproductive related traits of Kobresia humilis

放牧处理 Grazing treatment	种子性状 Seed trait	生殖相关性状 Reproductive related trait
放牧处理 Grazing treatment	种子性状 Seed trait	个体总质量 Total individual mass	生殖枝质量占比 Proportion of reproductive branch mass	单条生殖枝质量 Mass of single reproductive branch	个体种子总质量 Total individual seed mass
牦牛单独放牧 Single yak grazing (Y)	种子大小 Seed size	0.275	0.318	0.298	0.408^*
藏羊单独放牧 Single Xizang sheep grazing (S)		0.076	0.039	0.172	0.241
牦牛藏羊1:2混牧 Yak:Xizang sheep grazing ratio of 1:2 (M1)		0.014	0.132	0.335	0.258
牦牛藏羊1:4混牧 Yak:Xizang sheep grazing ratio of 1:4 (M2)		0.181	0.112	0.535^**	0.391^*
牦牛藏羊1:6混牧 Yak:Xizang sheep grazing ratio of 1:6 (M3)		0.090	0.069	0.223	0.285
不放牧 No grazing (CK)		0.234	0.280	-0.114	0.432^*
Y	种子数量 Seed number	0.738^**	0.459^*	0.112	0.915^**
S		0.299^*	0.746^**	0.273	0.937^**
M1		0.553^**	0.495^**	0.352	0.929^**
M2		0.706^**	0.532^**	0.062	0.869^**
M3		0.779^**	0.386^*	0.245	0.910^**
CK		0.594^**	0.626^**	-0.019	0.965^**

Fig. 6 Trade-off relationship between seed size and seed number of Kobresia humilis under different grazing treatments. CK, no grazing; M1, M2 and M3 representing yak and Xizang sheep grazing ratios with 1:2, 1:4 and 1:6; S, single Xizang sheep grazing; Y, single yak grazing.

Fig. 7 Variable importance in projection values (VIP) of seed size and seed number trade-off by reproductive related traits under different grazing treatments. CK, no grazing; M1, M2 and M3 representing yak and Xizang sheep grazing ratios with 1:2, 1:4 and 1:6; S, single Xizang sheep grazing; Y, single yak grazing. RMP, proportion of reproductive branch mass; SRM, mass of single reproductive branch; TM, total individual mass; TSM, total individual seed mass. The dotted line indicates VIP = 1.

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