Abstract Dew is commonly regarded as an important water source for lichens. This is also the case for crustose lichens that are attached to the substrate, whether rocks or soil. While being verified during ample research on rock-dwelling lichens in the Negev, the findings from soil-dwelling lichens (lichen biocrusts) are not conclusive. In the Tabernas Desert, the soil surface is characterized by a lush cover of crustose lichens. These soil biocrusts (biological soil crusts) were reported to use dew for photosynthesis while, at the same time, it was also observed that these crustose chlorolichens are relatively non-wettable. In an attempt to explore the apparent controversy, two year-long meteorological data (minimum air temperature and relative humidity, RH), during which chlorolichens were thought to utilize dew for photosynthesis (2006–2007) were analyzed. The analysis includes a comparison to the meteorological conditions that prevailed in the Negev during 135 days of manual dew measurements. As found for the Negev, net photosynthesis by the chlorolichens is expected once the RH, as measured at the meteorological station, is ≥90% while vapor condensation (dew) is expected once RH is ≥95%. RH in the Negev was substantially higher than the average RH of 75.0–87.2% registered during the rainless days of 2006–2007 in the Tabernas, implying that RH in the Tabernas is too low to facilitate frequent dew formation and net photosynthesis by the lichens. Photosynthesis in the Tabernas is mainly confined to rainy periods, taking place either due to direct wetting by rain, or following vapor condensation from the subsurface (distillation). Our findings do not support the view that dew is an important water source for the establishment and growth of crustose soil lichens in the Tabernas. Moreover, the low RH in the Tabernas may also imply that dew may only have a very limited role in providing water to lithobionts in this ecosystem.

中文翻译：

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大气湿度不太可能成为塔伯纳斯沙漠中硬壳土壤地衣的重要水源

摘要 露水通常被认为是地衣的重要水源。对于附着在岩石或土壤等基质上的硬壳地衣来说也是如此。尽管在对内盖夫岩栖地衣的大量研究中得到了验证，但土栖地衣（地衣生物结皮）的发现并不是决定性的。在塔贝纳斯沙漠，土壤表面的特征是茂密的硬壳地衣。据报道，这些土壤生物结皮（生物土壤结皮）利用露水进行光合作用，同时还观察到这些结皮的绿地衣相对不可润湿。为了探索明显的争议，两年的气象数据（最低气温和相对湿度，RH），在此期间，绿地衣被认为利用露水进行光合作用（2006-2007 年）进行了分析。该分析包括与内盖夫在 135 天的人工露水测量期间盛行的气象条件的比较。正如内盖夫发现的那样，一旦气象站测量的 RH ≥ 90%，预计会发生绿地衣的净光合作用，而一旦 RH ≥ 95%，预计会发生蒸汽冷凝（露水）。内盖夫的相对湿度大大高于 2006 年至 2007 年塔贝纳斯无雨天记录的平均相对湿度 75.0-87.2%，这意味着塔贝纳斯的 RH 太低，无法促进地衣频繁的露水形成和净光合作用。Tabernas 的光合作用主要限于雨季，发生的原因可能是雨水直接润湿，或跟随来自地下的蒸汽冷凝（蒸馏）。我们的研究结果不支持露水是 Tabernas 结壳土壤地衣建立和生长的重要水源的观点。此外，Tabernas 的低 RH 也可能意味着露水在为该生态系统中的岩石生物提供水方面的作用可能非常有限。