Biological soil crusts (biocrusts) are living ground covers that result from intimate associations between soil particles and organisms, which can modify soil properties and support fundamental ecosystem functions in drylands. Despite numerous studies concerning effects of biocrusts on soil hydrological processes, their impacts on grassland evapotranspiration have remained unanswered. By using micro-lysimeters, we conducted in-situ monitoring of evapotranspiration of bare soil cyanobacterial-moss mixed biocrusts, gramineous grass gramineous grass with biocrusts, and leguminous grass leguminous grass with biocrusts over two months in a semi-arid ecosystem. Results suggested that compared to the bare soil, the biocrusts significantly increased soil evaporation rate by 20.9 %. Underneath gramineous and leguminous grasses, the biocrusts increased the average evapotranspiration rate by 9.4 % and 13.4 %. The evaporation of biocrusts contributed 8.1–10.6 % to the average evapotranspiration rate and 8.2–12.6 % to the cumulative evapotranspiration amount. Additionally, the biocrusts increased soil moisture by 12.5 % and decreased temperature by 3.4 % at 10 cm depth compared to the bare soil. However, the biocrusts beneath grasses led to a reduction in soil moisture by 10.0 % and 20.0 %, while causing an increase in temperature by 9.9 % and 2.9 %, respectively. Enhanced evaporation of the biocrusts could be mainly attributed to their higher water retention ability in comparison to the bare soil. Meanwhile, beneath grasses, the biocrusts decreased soil water content in deeper layers, potentially limited grass transpiration by reducing water availability for grass roots. Based on these results, we concluded that the biocrusts intensify grassland evapotranspiration through increasing soil evaporation and reducing grass transpiration. Our findings highlight that biocrusts play a crucial role in modulating surface water fluxes, potentially exert remarkable effects on dryland vascular plants development and ecosystem stability.

中文翻译：

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生物结皮通过增加半干旱生态系统中的蒸发和减少蒸腾来强化草原蒸散


生物土壤结皮（生物结皮）是由土壤颗粒和生物体之间密切联系产生的活地被植物，它可以改变土壤特性并支持旱地的基本生态系统功能。尽管有大量关于生物结皮对土壤水文过程的影响的研究，但它们对草地蒸散量的影响仍未得到解答。利用微型蒸渗仪，对半干旱生态系统中裸土蓝藻-苔藓混合结皮、禾本科禾本科带生物结皮、豆科禾本科带生物结皮的蒸散量进行了两个多月的原位监测。结果表明，与裸土相比，生物结皮使土壤蒸发率显着增加了20.9%。在禾本科和豆科草下面，生物结皮使平均蒸散率增加了9.4%和13.4%。生物结皮的蒸发对平均蒸散率的贡献率为8.1%~10.6%，对累积蒸散量的贡献率为8.2%~12.6%。此外，与裸土相比，生物结皮使 10 厘米深度的土壤湿度增加了 12.5%，温度降低了 3.4%。然而，草下的生物结皮导致土壤湿度降低 10.0% 和 20.0%，同时导致温度分别升高 9.9% 和 2.9%。生物结皮蒸发的增强主要归因于其比裸土具有更高的保水能力。与此同时，在草下，生物结皮降低了深层土壤含水量，通过减少草根的可用水量，可能限制草的蒸腾作用。 基于这些结果，我们得出结论，生物结皮通过增加土壤蒸发和减少草地蒸腾来加剧草地蒸散。我们的研究结果强调，生物结皮在调节地表水通量方面发挥着至关重要的作用，可能对旱地维管植物发育和生态系统稳定性产生显着影响。