Many semi-arid savannas are prone to degradation, caused e.g. by overgrazing or extreme climatic events, which often lead to shrub encroachment. Overgrazing by livestock affects vegetation and infiltration processes by directly altering plant composition (selective grazing) or by impacting soil physical properties (trampling). Water infiltration is controlled by several parameters, such as macropores (created by soil-burrowing animals or plant roots) and soil texture, but their effects have mostly been studied in isolation. Here we report on a study, where we conducted infiltration experiments to analyze the interconnected effects of invertebrate-created macropores, shrubs and soil texture (sandy soil and loamy sand) on infiltration in two Namibian rangelands. Using structural equation modeling, we found a direct positive effect of shrub size on infiltration and indirectly via invertebrate macropores on both soil types. On loamy sands this effect was even stronger, but additionally, invertebrate-created macropores became relevant as a direct driver of infiltration. Our results provide new insights into the effects of vegetation and invertebrates on infiltration under different soil textures. Pastoralists should use management strategies that maintain a heterogeneous plant community that supports soil fauna to sustain healthy soil water dynamics, particularly on soils with higher loam content. Understanding the fundamental functioning of soil water dynamics in drylands is critical because these ecosystems are water-limited and support the livelihoods of many cultures worldwide.

中文翻译：

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半干旱稀树草原草地灌木、无脊椎动物衍生的大孔隙和土壤质地对水入渗的相互影响

许多半干旱稀树草原易于退化，例如由过度放牧或极端气候事件引起，这通常会导致灌木侵占。牲畜过度放牧通过直接改变植物组成（选择性放牧）或影响土壤物理特性（践踏）来影响植被和渗透过程。水渗透受几个参数控制，例如大孔隙（由挖土动物或植物根部产生）和土壤质地，但它们的影响大多是单独研究的。在这里，我们报告了一项研究，在该研究中，我们进行了渗透实验，以分析无脊椎动物产生的大孔、灌木和土壤质地（沙土和壤土）对两个纳米比亚牧场渗透的相互影响。使用结构方程建模，我们发现灌木大小对入渗有直接的积极影响，并通过无脊椎动物大孔对两种土壤类型产生间接影响。在肥沃的沙滩上，这种影响甚至更强，但此外，无脊椎动物产生的大孔成为渗透的直接驱动因素。我们的研究结果为不同土壤质地下植被和无脊椎动物对渗透的影响提供了新的见解。牧民应使用管理策略来维持支持土壤动物群的异质植物群落，以维持健康的土壤水分动态，尤其是在壤土含量较高的土壤上。了解旱地土壤水动态的基本功能至关重要，因为这些生态系统缺水并支持全世界许多文化的生计。