Salinity and sodicity are major forms of land degradation in drylands worldwide, reducing soil function, and threatening pastoral livelihoods. Dryland soils are often dominated by biocrusts, surface aggregations of lichens, bryophytes, fungi and other minute organisms that stabilize surface soils. Biocrusts could have a role in maintaining hydrological functions in heavily salinized areas, but there have been few studies, and the mechanisms are poorly understood. We tested whether biocrust mosses and lichens enhanced infiltration, and reduced runoff and sediment yield, on biocrusted islands scattered among extensive patches of bare highly saline soils in northeaster Iran. Biocrusted soils had greater cumulative infiltration and hydraulic conductivity, less runoff, which commenced later, and lower sediment yields than bare soils. The water content of biocrusted soils was greater than bare soils, but only at low matric potentials. Biocrusted surfaces were alkaline, more sandy, had lower levels of sodium, chloride, and calcium-plus-magnesium ions, and a lower sodium absorption ratio than bare soils. Structural equation modelling showed that increasing salinity was associated with a suppression of the negative effect of biocrusts on runoff. Potential mechanisms for reduced runoff likely relate to enhanced soil aggregation and porosity of biocrusted soils leading to greater retention of soil water content at low matric potentials, as well as an ability of mosses and lichens to capture and store surface water or to permit infiltration into the uppermost surface layers. Overall, our findings reveal a strong association between moss- and lichen-dominant biocrusts and soil hydrological processes, and suggest that these crusts play an important role in maintaining hydrological function in heavily salinized soils.

盐度和碱度是全球旱地土地退化的主要形式，会降低土壤功能并威胁牧区生计。旱地土壤通常以生物结皮、地衣、苔藓植物、真菌和其他稳定地表土壤的微小生物的表面聚集体为主。生物结皮可能在盐渍化地区维持水文功能方面发挥作用，但研究很少，其机制也知之甚少。我们测试了生物结皮苔藓和地衣是否会在伊朗东北部散布在大片裸露高盐分土壤中的生物结皮岛屿上增强渗透，并减少径流和沉积物产量。与裸土相比，生物结皮土壤具有更大的累积入渗和水力传导率、更少的径流（开始较晚）和更低的沉积物产量。生物结皮土壤的含水量大于裸土，但仅在低基质势时。与裸土相比，生物结皮表面呈碱性，多沙，钠、氯和钙加镁离子的含量较低，钠吸收率也较低。结构方程模型表明，增加盐度与抑制生物结壳对径流的负面影响有关。减少径流的潜在机制可能与增强的土壤聚集和生物结皮土壤的孔隙率有关，从而导致在低基质势下土壤含水量的更大保留，以及苔藓和地衣捕获和储存地表水或允许渗入地表水的能力最上表面层。全面的，