Climate change-driven increases in aridity will lead to dryland expansion worldwide. In the Atlantic and Mediterranean biogeographic regions, coastal dunes are priority conservation areas highly sensitive to aridification where plants and biological soil crusts may play a key role maintaining ecosystem services. However, we still need further insights into the balance between the effects of increasing aridity and the influence of local vegetation on the soil attributes and functioning of these systems, particularly in transitional areas between humid and arid climatic zones. We sampled 24 dune systems distributed along a natural climate gradient including humid, dry-subhumid and arid environments in the Atlantic coastline of the Iberian Peninsula and investigated (i) how aridity drives the vegetation community structure, soil biotic and abiotic properties and functions in dune ecosystems at a regional scale; and (ii) to what extent soil attributes differ locally under diverse surface microsites (i.e. plants, biocrust and bare soil). Increasing aridity in coastal dunes decreased total biotic cover and favoured the formation of shrub-dominated patches. Vegetation shifts were accompanied by declines in soil microbial diversity, organic matter, nutrient contents and reduced rates of N mineralization. Soil bacterial communities were more sensitive to aridity than fungal communities. Microsites were essential regulators of soil attributes, and their effects were dependent on the degree of aridity. In drylands, shrub microsites were associated to higher soil organic C, microbial (bacterial and fungal) abundance, fungal diversity and potential heterotrophic respiration than bare microsites, likely due to enhanced litter and sediment redistribution. However, at humid and transition systems, microsites controlled soil N pools and microbial diversity, suggesting tight linkages between vegetation patches and soil microorganisms responsible for N availability. These findings provide evidence of the strong negative impacts of aridification on vegetation attributes and nutrient cycling in coastal dunes and highlight the role of the biotic cover in preserving soil fertility, microbial diversity and functioning, particularly in the most arid sites.

由气候变化驱动的干旱增加将导致全球旱地扩张。在大西洋和地中海生物地理区域，沿海沙丘是对干旱高度敏感的优先保护区，那里的植物和生物土壤结皮可能在维持生态系统服务中发挥关键作用。但是，我们仍然需要进一步了解干旱增加的影响与当地植被对土壤属性和这些系统的功能之间的平衡，特别是在湿润和干旱气候带之间的过渡地区。我们采样了24个沙丘系统，这些系统沿自然气候梯度分布，包括伊比利亚半岛大西洋海岸线上的潮湿，干湿，半湿润和干旱环境，并研究（i）干旱如何驱动植被群落结构，沙丘生态系统在区域范围内的土壤生物和非生物特性和功能；（ii）在不同的表面微地点（即植物，生物结皮和裸露的土壤）下，土壤属性在何种程度上局部不同。沿海沙丘的干旱加剧，减少了生物总量，并有利于灌木为主的斑块的形成。植被变化伴随着土壤微生物多样性，有机质，养分含量的下降和氮矿化速率的降低。土壤细菌群落比真菌群落对干旱更敏感。微型场地是土壤属性的重要调节者，其作用取决于干旱程度。在干旱地区，灌木丛中的微地点与土壤中较高的有机碳，微生物（细菌和真菌）的丰度有关，真菌的多样性和潜在的异养呼吸比裸露的微场所要多，这可能是由于凋落物和沉积物的重新分配增加了。但是，在湿润和过渡系统中，微场所控制着土壤氮库和微生物多样性，这表明植被斑块与负责氮素利用的土壤微生物之间的紧密联系。这些发现提供了干旱化对沿海沙丘植被特征和养分循环的强烈负面影响的证据，并突出了生物覆盖物在保持土壤肥力，微生物多样性和功能方面的作用，特别是在最干旱的地区。这表明植被斑块与土壤微生物之间的紧密联系导致氮的有效性。这些发现提供了干旱化对沿海沙丘植被特征和养分循环的强烈负面影响的证据，并突出了生物覆盖物在保持土壤肥力，微生物多样性和功能方面的作用，特别是在最干旱的地区。这表明植被斑块与土壤微生物之间的紧密联系导致氮的有效性。这些发现提供了干旱化对沿海沙丘植被特征和养分循环的强烈负面影响的证据，并突出了生物覆盖物在维护土壤肥力，微生物多样性和功能方面的作用，特别是在最干旱的地区。