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Grazing Offsets Nitrogen Enrichment Effects on Species Richness by Promoting the Random Colonization of Local Species in an Alpine Grassland
Ecosystems ( IF 3.7 ) Pub Date : 2019-05-29 , DOI: 10.1007/s10021-019-00403-8
Ming-Hua Song , Jin Chen , Xing-Liang Xu , Yi-Kang Li , Jun-Qin Gao , Hua OuYang

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.



中文翻译:

通过促进高寒草原本地物种的随机定居,放牧抵消了氮素富集对物种丰富度的影响。

氮(N)引起的物种丰富度下降可以通过抑制优势种增加地面光来抵消。然而,就分类学或性状而言,尚不知道放牧介导的本地定居物种是否对应于N诱导的本地灭绝物种。分析了来自11年的氮添加和冬季放牧实验的数据,以评估社区和功能组水平的物种丰富度动态。关于氮的处理,在最初的7年中进行围封和氮添加,然后在接下来的4年中进行冬季放牧并连续添加氮。此外,所有处理方法均用于比较N诱导的局部物种灭绝和放牧介导的局部物种定殖。然后,N诱导的局部灭绝物种和放牧介导的局部定殖物种的性状与植物性状进一步相关。我们发现,由于随机和非随机物种损失,氮的添加导致植物物种丰富度的下降。丢失的物种与性状密切相关,包括低高度,非克隆性,低特殊叶面积(SLA)和低叶氮浓度,这些与光捕获能力有关。相反,放牧促进了当地稀有物种的随机定居,从而抵消了氮引起的物种丰富度下降。但是,非随机丢失的物种无法通过放牧来挽救。放牧介导的本地定居物种通常以高叶片碳(C)浓度,SLA和种子质量为特征。

更新日期:2020-04-21
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