Linkages of plant diversity and functional groups to aboveground productivity upon alpine grassland degradation

doi:10.17521/cjpe.2024.0143

Abstract

Abstract:

Aims During the past decades, about a half of the global grasslands have been degraded as the results of climate change and anthropogenic activities. Grassland degradation substantially alters plant diversity and community composition; however, it remains elusive how these changes link to ecosystem productivity across broad geographic scales.

Methods Using a standardized survey from 45 grassland degradation sequences at 15 sites across three grassland types (i.e., alpine steppe, alpine meadow and alpine swamp meadow) on the Qingzang Plateau, we aim to explore changes in plant diversity and functional groups upon grassland degradation and their linkages with aboveground net primary productivity (ANPP).

Important findings Across the three grassland types, species richness, Shannon-Weiner diversity index, Simpson diversity index and Pielou evenness index all exhibited a first increase and then decrease pattern as degradation intensified. The coverage of sedge and grass declined, but legume coverage showed no significant changes and forb coverage increased along the degradation gradient. Mixed-effects models showed that degradation-induced change in ANPP was mainly associated with changes in coverage of original dominant species but minimally influenced by plant diversity for all grassland types. These results indicate that the degradation-induced productivity reduction is caused by the decline in dominant species rather than losses of plant diversity. The findings mentioned above provide important clues for alpine grassland restoration: restoring dominant species would be an effective approach for boosting ecosystem productivity in degraded grasslands on the Qingzang Plateau.

Key words: plant diversity, functional groups, vegetation productivity, grassland degradation, alpine grassland

NIU Ya-Ping, GAO Xiao-Xia, YAO Shi-Ting, YANG Yuan-He, PENG Yun-Feng. Linkages of plant diversity and functional groups to aboveground productivity upon alpine grassland degradation[J]. Chin J Plant Ecol, 2025, 49(1): 83-92.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0143

https://www.plant-ecology.com/EN/Y2025/V49/I1/83

Figures/Tables 5

Fig. 1 Location of sampling sites across the Three-River Source Region. The vegetation map is generated from Vegetation Atlas of China with a scale of 1:1 000 000 (The Editorial Committee of Vegetation Map of China, Chinese Academy of Sciences, 2007).

Fig. 2 Changes in species richness (A), Shannon-Weiner diversity index (B), Simpson diversity index (C), Pielou evenness index (D) and coverage of different functional groups (E-H) along degradation gradients in various grassland types (mean ± 95%CI). Different lowercase letters represent significant differences among different degradation levels (p < 0.05); ns, p > 0.05. AM, alpine meadow; AS, alpine steppe; ASM, alpine swamp meadow; HD, heavy degradation; MD, moderate degradation; ND, non-degradation; SD, slight degradation.

Table 1 Changes in soil properties along degradation gradients in various alpine grassland types (mean ± SD)

草地类型 Grassland type	退化程度 Degradation level	土壤pH Soil pH	土壤容重 Soil bulk density (g·cm^-3)	土壤含水率 Soil moisture (%)	铵态氮含量 NH₄⁺-N content (mg·kg^-1)	硝态氮含量 NO₃^--N content (mg·kg^-1)
高寒草原 AS	未退化 ND	8.51 ± 0.19^b	1.14 ± 0.17^b	12.34 ± 3.93^a	4.81 ± 1.43^a	4.71 ± 1.90^a
	轻度退化 SD	8.58 ± 0.20^a	1.19 ± 0.15^ab	12.44 ± 3.58^a	4.79 ± 2.02^a	4.18 ± 1.83^ab
	中度退化 MD	8.57 ± 0.17^a	1.24 ± 0.18^ab	11.86 ± 3.37^a	4.32 ± 1.67^a	3.71 ± 1.67^b
	重度退化 HD	8.60 ± 0.18^a	1.26 ± 0.19^a	12.31 ± 2.85^a	3.12 ± 1.47^b	3.54 ± 1.93^b
高寒草甸 AM	未退化 ND	6.71 ± 0.74^b	0.75 ± 0.18^b	48.29 ± 16.05^a	25.44 ± 14.91^a	4.63 ± 3.41^b
	轻度退化 SD	6.77 ± 0.78^b	0.81 ± 0.21^b	45.75 ± 18.23^a	17.03 ± 7.13^b	4.71 ± 3.53^b
	中度退化 MD	7.11 ± 0.78^a	0.93 ± 0.22^a	34.07 ± 11.24^b	13.00 ± 8.13^c	6.41 ± 3.71^a
	重度退化 HD	7.21 ± 0.83^a	0.98 ± 0.22^a	25.47 ± 8.74^c	5.37 ± 3.84^d	7.15 ± 3.74^a
高寒沼泽化草甸 ASM	未退化 ND	6.94 ± 0.72^c	0.44 ± 0.11^c	143.34 ± 28.84^a	23.50 ± 7.61^a	3.10 ± 1.56^b
	轻度退化 SD	7.06 ± 0.81^bc	0.59 ± 0.22^b	109.39 ± 37.27^b	22.77 ± 7.54^a	5.87 ± 5.14^ab
	中度退化 MD	7.17 ± 0.84^b	0.75 ± 0.30^a	83.29 ± 49.36^c	13.69 ± 4.33^b	8.71 ± 9.18^a
	重度退化 HD	7.37 ± 0.74^a	0.89 ± 0.24^a	47.22 ± 34.12^d	4.27 ± 1.32^c	10.18 ± 6.25^a

Fig. 3 Relationships of plant diversity and coverage of functional groups with environmental factors along degradation gradients in different grassland types. The response ratio, which was calculated as the natural logarithm of the ratio of degradation plots to non-degradation plots, was used in regression analysis to account for spatial heterogeneity among different sampling sites. AM, alpine meadow; AS, alpine steppe; ASM, alpine swamp meadow; MAP, mean annual precipitation; MAT, mean annual air temperature. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Fig. 4 Changes in aboveground net primary productivity (ANPP) along degradation gradients in various grassland types (A, mean ± 95% CI), relationships of ANPP with plant diversity and coverage of functional groups (B), and moderators of ANPP based on relative influence of predictor variables in the random forest model (C). In A, different lowercase letters represent significant difference among different degradation levels (p < 0.05). In B, the solid circles indicate significant effects (p < 0.05), the hollow circles indicate non-significant effects (p > 0.05) and the error bars denote 95% confidence intervals. In C, the response ratio, which was calculated as the natural logarithm of the ratio of degradation plots to non-degradation plots, was used in univariate regression and random forest analyses to account for spatial heterogeneity among different sampling sites. AM, alpine meadow; AS, alpine steppe; ASM, alpine swamp meadow; HD, heavy degradation; MAP, mean annual precipitation; MAT, mean annual air temperature; MD, moderate degradation; ND, non-degradation; SD, slight degradation.

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