The consequences of using microlysimeters: Why microlysimeters grossly overestimate dew amounts in arid regions? A critical review.

Although commonly considered the gold standard for measurement of non-rainfall water (NRW), providing reasonable reliable data for vegetated soils, microlysimeters (MLs) tend to grossly overestimate NRW (primarily in form of dew) on barren soil. In arid and semiarid regions, the reported values may be overestimated by hundreds and even 1000 %. This bias is attributed to (i) the effect of the structure and dimension of the ML (ii) the tacit assumption that the weight difference between morning and the previous midday/evening results from dew or (iii) the belief that the MLs will provide reliable values if the difference in weight would be calculated only from the evening or night. For instance, from the time during which the air temperature reaches the dewpoint temperature or from the time during which condensation takes place on an adjacent leaf-wetness sensor. Calculating dew by the weight difference of MLs led to the notions that the fine-textured soil will necessarily promote higher values of dew, and the notion that higher amounts of dew are expected following days with low relative humidity, both of which hamper our understanding regarding dew formation. The reasons for the apparent different performance of MLs in vegetated (wet) and barren (arid) regions are discussed.

The effect of the water source on niche partioning of chlorolichens and cyanobacteria-implications for resilience?

MAIN CONCLUSION: Microclimate determines lichens and cyanobacteria distribution in the Negev, with lichens and cyanobacteria inhabit dewy and dewless habitats, respectively. Lichens experiences more frequent and extensive environmental fluctuations than cyanobacteria. The spatial partitioning of chlorolichens (eukaryotes) and cyanobacteria (prokaryotes) are intriguing, especially following recent intense search for extraterrestrial life. This is especially relevant for deserts, where both lithobionts are thought to use rain and dew but may differ in their resilience to environmental extremes and fluctuations. Following the different spatial distribution of lithobionts in a south-facing slope of the Negev Highlands (with cyanobacteria-inhabiting rocks and chlorolichen-inhabiting cobbles), measurements of temperature, non-rainfall water (NRW) and biomass were carried out within the drainage basin aiming to test the hypotheses that (i) cobble-inhabiting lichens may access more water (through NRW) and may be subjected to more extensive environmental fluctuations of temperature and water than bedrock-inhabiting cyanobacteria, and (ii) will therefore have a greater contribution to the ecosystem productivity. In contrast to cyanobacteria, cobble-inhabiting chlorolichens were found to access NRW (up to 0.20 mm of daily amounts in comparison to < 0.04 mm of the cyanobacteria) and to experience higher fluctuations of temperatures (up to 4.1 °C higher and 5.3 °C lower). With lichens and cyanobacteria inhabiting dewy and dewless habitats, respectively, NRW was found responsible for contributing 6.8-fold higher organic carbon to the lithobiontic community. At this site, chlorolichens experience more extensive environmental fluctuations than cyanobacteria, possibly indicating a higher tolerance for environmental fluctuations. These observations may assist in the interpretation of the abiotic conditions responsible for past or present lithobiontic life on Mars.

Dew and fog as possible evolutionary drivers? The expansion of crustose and fruticose lichens in the Negev is respectively mainly dictated by dew and fog.

MAIN CONCLUSION: The expansion of crustose lichens in the Negev is principally determined by dew and that of fruticose lichens by fog. Crustose and fruticose lichens are largely adapted to dew and fog, respectively. Although crustose and fruticosea lichens were shown to efficiently use dew and fog, the link between their expansion and the occurrence of dew and fog has never been shown experimentally. This is also the case for the Negev Desert Highlands, where (i) dewless habitats were not inhabited by lichens and (ii) an increase in fruticose lichens with high-altitude fog-prone areas was noted, leading us to hypothesize that the expansion of crustose and fruticose lichens is mainly linked to dew and fog, respectively. Experiments aiming to compare the non-rainfall water (NRW) were conducted. We used cloths attached to 7 cm-high cobbles to mimic crustose lichens (MCL), cloths placed horizontally aboveground to evaluate the amount of NRW without the presence of the cobble (CoP), cloths attached to a wire scaffold mimicking fruticose lichens (MFL), and cloths attached to glass plates (CPM) that served as a reference. Substrate temperatures were compared to the dew point temperature. In addition, sprinkling experiments, which mimicked fog under variable wind speeds (0.9, 1.4, 3.3 and 5.7 m s-1), were also conducted. NRW followed the pattern: MCL ≈ CPM > CoP > > MFL. While MCL yielded substantially higher amounts of NRW (0.09 mm) in comparison to MFL (0.04 mm) during dew events, similar amounts were obtained by both substrates (0.15-0.16 mm) following fog. However, fog interception increased substantially with wind speed. The findings may explain the expansion of crustose lichens in extreme deserts benefiting mainly from dew (but also fog), and the proliferation of fruticose lichens in fog-prone areas, especially when accompanied by high-speed winds. While (mainly) high proliferation of crustose lichens may serve as bioindicators for dew in extreme deserts, fruticose lichens may serve as bioindicators for fog.