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Abstract: We studied the lichen diversity on cobbles at 18 stations located within 4 aspects of a second order drainage basin near Sede Boqer at the Negev Highlands, Israel, where dew was found to be the main water source for lichens. At each station 10 cobbles were randomly chosen and the lichen community composition and structure were investigated and compared to the dew amount and duration that characterize each station. Excluding the wadi stations that showed a very heterogeneous population (probably originating from cobbles that rolled down from both adjacent slopes) and were therefore excluded from the analysis, all other stations were grouped into 5 clusters that showed a close link with the dew moisture regime. Lichen distribution pointed to species which can serve as biomarkers for dew amount and especially for dew duration. The data imply that at a meso-scale, lichens can provide information regarding the dew regime of habitats where no microclimatological data are available. [Copyright &y& Elsevier]

Dew and rain were measured along the north facing slope (NFS, with epilithic lichens predominating) and the south-facing slope (SFS, with endolithic lichens predominating) in the Negev (P = 95 mm) in order to evaluate the relationships between the abiotic conditions and the lichen growth form. Although insignificant differences characterize the rain and dew amounts with the epilithic growth form, high correlation was obtained between dew duration (r2 = 0.73) and the combined duration of dew and rain (r2 = 0.79). The data imply that daylight wetness duration rather than the amount of precipitation may explain the predominance of epilithic lichens at the shaded NFS. [ABSTRACT FROM AUTHOR]

Rock slabs were placed from 1991 through 2006 at the bottom of a north- (NFS) and a south-facing (SFS) slope of a first order drainage basin in the Negev Desert Highlands, Israel (P = 95 mm) where natural cobbles have >95% cover of endolithic and epilithic lichens. Periodic measurements of rain, dew and chlorophyll content took place. Lichen cover and the regeneration time were aspect-dependent. Lichen cover was 98% and 61% at NFS and SFS, respectively, while the lichen's recovery time was respectively ∼45 and ∼80 years. The fast regeneration time may have important implications regarding weathering and soil formation. [ABSTRACT FROM AUTHOR]

Whereas the role of the photobiont within microlichen symbiosis is indisputable, the role of the mycobiont in the symbiosis is still questionable. Here we report a unique expansion of the endolithic lichen Caloplaca alociza on cobbles in the Negev Desert due to structural change induced by the mycobiont burrowing activity. By increasing the water-holding capacity of the rock it facilitates lichen expansion from the cobble margins (where they establish due to water capillary rise) to its sides. And thus, while rare at the cobble top, lichen expansion is taking place to the sides of the cobble albeit the fact that dew (the main water source) is significantly lower at the cobble sides than at its top. [ABSTRACT FROM AUTHOR]