Abstract. Biological soil crusts (biocrusts) composed of cyanobacteria, bacteria, algae, fungi, lichens, and bryophytes stabilize the soil surface. This effect has mainly been studied in arid climates, where biocrusts constitute the main biological agent to stabilize and connect soil aggregates. Besides, biocrusts are an integral part of the soil surface under mediterranean and humid climate conditions, mainly covering open spaces in forests and on denudated lands. They often develop after vegetation disturbances, when their ability to compete with vascular plants increases, acting as pioneer communities and affecting the stability of soil aggregates. To better understand how biocrusts mediate changes in soil aggregate stability under different climate conditions, we analyzed soil aggregate samples taken under biocrust communities from four national parks in Chile along a large climatic gradient ranging from (north to south) arid (Pan de Azúcar), semi-arid (Santa Gracia), mediterranean (La Campana) to humid (Nahuelbuta). Biocrust communities showed a stabilizing effect on the soil aggregates in dry fractions for the three northern and the wet aggregates for the southernmost sites. Here, permanent vascular plants and higher contents of organic carbon and nitrogen in the soil control aggregate stability more than biocrusts, which are in intense competition to higher plant communities. Moreover, we found an increase in stability for edge aggregate size classes (< 2.0 mm and 9.5–30.0 mm). The geometric mean diameter of the soil aggregates showed a clear effect due to the climatic gradient, indicating that the aggregate stability presents a log-normal instead of a normal distribution, with a trend of low change between aggregate size fractions. Based on our results, we assume that biocrusts affect the soil structure in all climates. Their role for aggregate stability is masked under humid conditions by higher vegetation and organic matter contents in the topsoil.

中文翻译：

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智利沿海山脉沿气候梯度的土壤团聚体稳定性的生物结皮相关变化

摘要。由蓝细菌、细菌、藻类、真菌、地衣和苔藓植物组成的生物土壤结皮（生物结皮）可以稳定土壤表面。这种效应主要在干旱气候下进行研究，其中生物结皮构成稳定和连接土壤团聚体的主要生物制剂。此外，在地中海和潮湿的气候条件下，生物结皮是土壤表面不可分割的一部分，主要覆盖森林中的空地和裸露的土地上。它们通常在植被干扰后发育，当它们与维管植物竞争的能力增加时，充当先锋群落并影响土壤团聚体的稳定性。为了更好地了解生物结皮如何调节不同气候条件下土壤团聚体稳定性的变化，我们分析了从智利四个国家公园沿大气候梯度从（北到南）干旱（Pan de Azúcar）、半干旱（Santa Gracia）、地中海（La Campana）到潮湿（纳韦尔布塔）。生物结皮群落对三个北部地区的干组分土壤聚集体和最南端的湿聚集体显示出稳定作用。在这里，永久性维管植物和土壤中较高的有机碳和氮含量比生物结皮更能控制团聚体稳定性，后者与高等植物群落竞争激烈。此外，我们发现边缘骨料尺寸等级（< 2.0 mm 和 9.5-30.0 mm）的稳定性有所提高。由于气候梯度，土壤团聚体的几何平均直径表现出明显的影响，表明聚集体稳定性呈现对数正态分布而不是正态分布，聚集体尺寸分数之间的变化趋势较小。根据我们的结果，我们假设生物结皮会影响所有气候下的土壤结构。它们对聚集体稳定性的作用在潮湿条件下被表层土壤中较高的植被和有机质含量所掩盖。