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首页> 外文期刊>Plant and Soil >The fertile island effect collapses under extreme overgrazing: evidence from a shrub-encroached grassland
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The fertile island effect collapses under extreme overgrazing: evidence from a shrub-encroached grassland

机译：肥沃的岛屿作用在极端过度灌注下崩溃：来自灌木侵犯草原的证据

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Background and aims Woody plant encroachment is a phenomenon of global concern in drylands due to demonstrated reductions in livestock carrying capacity. However, shrubs are known to contribute to the development of patches of enhanced fertility that might offset any negative effects of increasing grazing. We measured soil physical and chemical characteristics within shrub and open patches across a gradient in livestock grazing to explore how the relative effect of shrubs might change with increasing grazing-induced disturbance. Methods Soil carbon, nitrogen phosphorus and bulk density were measured within 92 shrub patches and their paired interspaces at five sites ranging from long-grazed to long-ungrazed in a semiarid grassland encroached by the N-fixing shrub Caragana microphylla. We used a combination of linear and structural equation modelling to test whether shrubs might buffer any negative effects of overgrazing on soils. Results Shrub soils were more porous, and had more organic carbon, nitrogen and phosphorus than interspace soils. Within both microsites, however, soil bulk density increased, and soil organic carbon and nutrients declined, with increasing grazing intensity. Grazing reduced interspace plant cover and height and exacerbated the negative effects of bulk density on soil carbon, whereas shrubs had the opposite effect. The relative importance of shrubs for soil carbon and nutrients increased with increasing grazing intensity but collapsed under extreme overgrazing. Conclusions These findings highlight the effect of grazing in promoting shrub dominance, which can also prevent grassland degradation. However, any positive effects of grazing collapsed when sites were severely overgrazed.
机译：背景和目标木质植物侵占是旱地的全球关注现象，因为牲畜携带能力的减少。然而，已知灌木有助于开发增强肥力的斑块，这可能抵消了增加放牧的任何负面影响。我们在灌木丛中测量土壤物理和化学特性，在牲畜放牧的梯度上打开贴片，以探讨灌木的相对效果如何随着草草引起的扰动而变化。方法在92个灌木贴片中测量土壤碳，氮磷和散装密度，在5位点的三个地点中测量其成对的间隙，从而在半干草地上侵占了N-固定的灌木粗蛋白酶脱噬细胞。我们使用了线性和结构方程模型的组合来测试灌木是否可以缓冲过度覆盖土壤的任何负面影响。结果灌木土壤越来越多孔，具有比间隙土壤更多的有机碳，氮和磷。然而，在微井中，土壤堆积密度增加，土壤有机碳和营养素下降，随着放牧强度的增加。放牧植物覆盖和高度减少，加剧了批量密度对土壤碳的负面影响，而灌木具有相反的效果。土壤碳和营养素灌木的相对重要性随着放牧强度的增加而增加，但在极端过度覆盖下倒塌。结论这些发现突出了放牧在促进灌木优势的效果，这也可以防止草地降解。然而，当网站严重过度吸引时，放牧的任何积极效应都会崩溃。

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