Grazing Offsets Nitrogen Enrichment Effects on Species Richness by Promoting the Random Colonization of Local Species in an Alpine Grassland

Nitrogen (N)-induced declines in species richness can be offset by grazing via the suppression of dominant species to increase ground-level light. However, it is not known whether grazing-mediated locally colonized species correspond to N-induced locally extinct species with regard to taxonomy or tr...

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Bibliographic Details
Published in:Ecosystems (New York) 2020-03, Vol.23 (2), p.278-291
Main Authors: Song, Ming-Hua, Chen, Jin, Xu, Xing-Liang, Li, Yi-Kang, Gao, Jun-Qin, OuYang, Hua
Format: Article
Language:English
Subjects:
Alpine ecosystems
Anthropogenic factors
Biomedical and Life Sciences
Colonization
Divergence
Dominant species
Ecology
Ecosystems
Endangered & extinct species
Environmental Management
Extinct species
Extinction (Biology)
Functional groups
Geoecology/Natural Processes
Grasslands
Grazing
Herbivores
Hydrology/Water Resources
Leaf area
Life Sciences
Local extinction
Mediation
Nitrogen
Nitrogen enrichment
Nutrient cycles
Offsets
Original Articles
Plant Sciences
Plant species
Population decline
Rare species
Species composition
Species extinction
Species richness
Taxonomy
Winter
Zoology
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Summary:Nitrogen (N)-induced declines in species richness can be offset by grazing via the suppression of dominant species to increase ground-level light. However, it is not known whether grazing-mediated locally colonized species correspond to N-induced locally extinct species with regard to taxonomy or traits. Data from 11 years of N addition and winter grazing experiments were analyzed to assess species richness dynamics at community and functional group levels. Regarding N treatments, enclosure and N addition were performed during the first 7 years and were then followed by winter grazing with continuous N addition during the next 4 years. Additionally, all treatments were used to compare N-induced local species extinction and grazing-mediated local species colonization. Then, traits of N-induced locally extinct species and grazing-mediated locally colonized species were further correlated with plant traits. We found that N addition induced a decline in plant species richness as a result of both random and non-random species losses. The lost species were closely associated with traits, including low height, non-clonality, low special leaf area (SLA), and low leaf N concentrations, which are relevant to light capture capacity. In contrast, grazing promoted the random colonization of local rare species, thus offsetting the N-induced decline of species richness. However, non-randomly lost species were not rescued by grazing. Grazing-mediated locally colonized species were generally characterized by high leaf carbon (C) concentrations, SLA, and seed mass. Our study provides experimental evidence indicating although grazing offsets N-induced species reduction, shifts in species composition and traits could cause a divergence in ecosystem function facing anthropogenic alterations to nutrient cycles and grazing.
ISSN:1432-9840
1435-0629
DOI:10.1007/s10021-019-00403-8