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Biological Soil Crusts (BSCs) are critical components of desert ecosystems worldwide. While all BSCs significantly modify the surfaces they occupy, the manner in which they affect their environment depends on the composition of the microphytic community. The aim of this paper is to study the hyperspectral thermal emissivity signatures of BSCs in order to identify and characterize them in a sand dune environment. The research was conducted in the northwestern Negev dunes. Measurements of several types of BSCs and bare soil were obtained using ground hyperspectral thermal sensors. We present an ability to spectrally separate different types of BSCs from bare sand, and to rank them according to successional development. Based on this ability, we created a spectral index for the discrimination of sand and BSCs of different types and applied it to multispectral remote sensing thermal images. This newly acquired ability to map different BSC types, using remote sensing, may lead to future applications of habitat and ecological function spatial mapping. We also demonstrate how a fusion of reflective and thermal data can be used to map different land-cover features in a sand dune environment. Our proposed thermal index not only discriminates sand and BSCs, but also enhances the signal from limestone pebbles more than other indices, based on reflective data. Unlike remote sensing in the reflective spectral region, thermal remote sensing is unconstrained by solar illumination. High resolution emissivity signatures of land cover are unaffected by environmental variables, as opposed to land-surface temperature that depends on the time of day and the season. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (BSCs) abound in the Hallamish dune field in the western Negev Desert, Israel. While their abundance may imply high adaptability to environmental change, such as fluctuations between wet and dry conditions following winter rains, summer rains, although rare, may also occur in the Hallamish dune field. The aim of the present paper is to examine crust responses to winter and summer rains, focusing particularly on its biomass components, chlorophyll and carbohydrate. In addition, species composition, during summer and winter was examined. Analysis took place during an exceptionally wet winter (1994/95 with 172mm) and a summer rainstorm (12.5.93 with 9.7mm). The data showed a 2–3 fold increase in chlorophyll a and total carbohydrates and a much richer species composition following the heavy winter rains of 1994/95. Yet, the data also showed ~15–30% decrease in the chlorophyll content of the crust (with no concomitant significant decrease in total carbohydrates) following the summer rainstorm. Intense weathering by the summer rain coupled with cell mortality may explain the decrease in the chlorophyll content following the summer rainstorm, suggesting possible changes in the BSC following a potential change in the precipitation regime due to global climate change. [Copyright &y& Elsevier]

Abstract: Dictating the length of time during which water is available, evaporation plays a cardinal role in ecosystem ecology and structure. This is especially so in arid and semi arid zones, where precipitation is highly limited. Covering the surface with a distinct 1–10cm thick layer, biocrusts (called also biological soil crusts or microbiotic crusts) may affect the evaporation rate and hence the water loss of the underlying parent material. Owing to their wide occurrence in arid and semi arid regions, examination of their impact upon the evaporation rate of the underlying soil is of special importance. The evaporation of water from sand covered by four types of cyanobacterial crusts and one moss-dominated crust in the Negev Desert was examined along with bare sand. The crusts and sand were subjected to wetting by rain and sprinkling (in Petri dishes and within 25cm diameter plots), and the crust and subcrust temperatures and moisture content were measured. In addition the albedo of the crusts was also measured. Whereas thick and high-biomass crusts tended to retain higher amounts of water in the Petri dishes, they were found to increase subsurface temperatures (by up to 3.9°C at 5cm depth) under field conditions, subsequently decreasing the 0–10cm moisture content. Moisture content at the crusted plots was significantly lower than that of non-crusted plot, with crusted plots having an evaporation rate of 1.24–1.57 (with average of 1.38) times higher than the bare sand. These findings were supported by field measurements under natural rain precipitation. In both cases, the field data under sprinkling and rain precipitation showed that the non-crusted surfaces retained their available moisture at the upper 10cm of the soil profile for 5–7days longer than that of the crusted surfaces. The findings may explain contradictory data published in the literature regarding field and lab experiments, and may point to the negative effect that biocrusts may have upon the soil water budget and hence on water availability for higher plants. [Copyright &y& Elsevier]

Abstract: The playas and microbiotic crust-covered interdunes are two geomorphological units in the Hallamish sand-dune field, Israel. As a depositional unit, a lack of vegetation and microbiotic crusts, as well as high contents of fine particles and salinity, may lead to low microbial activity and functional diversity at the playa. The present study was initiated in order to illuminate the spatiotemporal changes in the activity, biomass and metabolic profiles of soil microbial communities at the two habitats. Soil samples were collected from the 0–50-cm depth at the playa and interdune during the wet and dry seasons of 2010. Soil moisture and organic-carbon contents recorded at the playa were 2- to above 10-fold higher than at the crust-covered interdune throughout the study period. Nevertheless, opposite trends were recorded for fungal and bacterial CFUs, as well as microbial basal respiration and biomass, in most soil depths at the playa compared to the crust-covered interdune. The total substrate utilization rates of soil microbial communities fluctuated between 4.9 and 6.4 and between 3.9 and 14.9 μg CO2–C g−1 dry soil h−1 at the playa and interdune during the wet season, while 3-fold higher values were recorded at the two habitats during the dry season. The total substrate utilization rates, carbohydrates and carboxylic-acid utilization rates, and functional diversity of soil microbial communities at the playa, were lower than at the crust-covered interdune at most soil depths, while higher utilization rates of aromatic acid were recorded in at least three soil layers at the playa. [Copyright &y& Elsevier]

Abstract: Drylands are regarded as highly sensitive to climatic change. The putative positive relationship between average annual rainfall and runoff, assumed for areas between 100 and 300mm ignores the fact that climatic change in drylands is not limited to climatic factors alone, but is often accompanied by a parallel change in surface properties. Data on rainfall, runoff and soil moisture regime were collected at five monitoring sites in a sandy area, along a rainfall gradient from 86 to 160mm. Despite the uniform sandy substratum the frequency and magnitude of runoff declined with increasing annual rainfall. Under wetter conditions a thick topsoil biological crust develops. This crust is able to absorb and retain large rain amounts, limiting the depth to which water can penetrate, and therefore water availability for the perennial vegetation. In the drier area, the thin crust can absorb only limited rain amounts, resulting in surface runoff and deeper water infiltration at run-on areas. Our findings demonstrate the important role played by different types of biological soil crusts along the rainfall gradient considered, and question the generally held belief that higher rainfall necessarily leads to deeper water infiltration in sandy arid areas; and higher water availability for the perennial vegetation. [Copyright &y& Elsevier]

The coastal dunes of Israel have been undergoing a process of stabilization since 1948. One of the major features of this process is a change in the surface properties of the dunes – the development of a biological soil crust (BSC), and a change in the properties of the sand grains themselves. In Ashdod, at the southern coastal plain of Israel, sand properties that include the BSC, their fines (silt and clay) content and free iron-oxide (indicating their degree of rubification) have been analysed in detail using field and lab spectroscopy methods. In addition, sand erosion and deposition were measured using erosion pins to determine their effect on the presence of the above-mentioned factors. It was found that the BSC over these dunes is comprised of green algae that differs in its reflectance spectra from cyanobacterial crust, especially in the blue band. The crust was found to be particularly developed in the stable areas (mainly the interdunes) and on the north-facing slopes rather than on the south-facing slopes. A positive correlation was found between the crust fines and chlorophyll content, with stable areas showing more developed BSC. The stable areas showed also a lower albedo and slightly more developed reddish colour, indicating a slightly higher rate of rubification. This study demonstrates that the intensity of sand erosion/deposition rates affects soil properties, with the BSC being the fastest to react to the stabilization process (months to several years), followed by the content of fine particles (several years to a decade), whereas the rubification process is a much weaker marker and may need much longer time periods to develop (decades to centuries). [ABSTRACT FROM AUTHOR]

Abstract: We examined mycobiota structure, diversity level, and density of microfungal isolates in the biological soil crusts (BSC) and non-crusted soil of the northern and central Negev desert in 10 locations along a southward rainfall gradient. A total of 87 species from 49 genera were isolated. The mycobiota of BSC (80 species) was characterized by dominance of melanin-containing fungi, the remarkable contribution of sexual ascomycete species, and low abundance of the genera Penicillium and Aspergillus. Species richness and the contribution of dark-colored fungi with large, multicellular spores negatively and significantly correlated with rainfall. The comparison with mycobiota of the non-crusted soil showed that in BSC communities, the xeric “desert” component (melanics) was significantly more pronounced, and the mesic “forest” component (Penicillium) was much less represented. In addition, the weak influence of rainfall on spatial variations of most observed mycobiotic characteristics indicated that microenvironmental factors (soil moisture, temperature, organic matter content) influenced the development of studied communities more essentially than macroenvironmental (climatic) factors. [Copyright &y& Elsevier]

Aeolian dust is a significant source of phosphorus (P) in various ecosystems. The Saharan desert is the major dust source on earth and it contributes atmospheric P to terrestrial ecosystems which often depend on these inputs. Since estimations on the contribution of dust to the atmospheric P cycle vary between studies, accurate estimations on the aerosol-P inputs to ecosystems can be enhanced by an identification method for dust from the other atmospheric P sources. In the current study, we explored the use of the oxygen stable isotopes in phosphate, δ18O P , as a marker for desert dust P. To characterize the δ18O P in Saharan dust, we analyzed atmospheric particles sampled in Puerto Rico, which has good exposure in summer to African dust with little exposure to wildfires, local, or anthropogenic influence on atmospheric inputs. Additionally, to evaluate possible isotopic fractionations in desert dust sources, which could affect the soil δ18O P before transport, we analyzed the δ18O P in Israeli desert soils that served as an analog. Saharan dust storms sampled at Puerto Rico were found to have δ18O P values of 22.5 ± 0.3‰ in the resin fraction (which represents labile inorganic P), similar to previously reported values of Saharan dust sampled in Israel. The data from Israel desert soils demonstrated that biological activity in desert crusts can have a small effect (with a maximum difference of 3.3‰ between the topsoil and the subsoil) on the δ18O P of desert soils, mainly when developed soil crust is present, as a result of intracellular isotopic equilibration between oxygen in phosphate and soil water. However, biological crusts are not considered a major dust source. Additionally, Saharan dust sampled in Israel and in Puerto Rico had a δ18O P similar to apatite minerals derived from sedimentary phosphorites. Thus, we suggest the dust source had little or no biological activity. Furthermore, the δ18O P in Saharan dust was distinctive from other atmospheric P sources, such as pollen and wildfire ash, and as a result, the δ18O P can be used to distinguish between these atmospheric P main sources. • Atmospheric dust is an important source of P for many ecosystems. • We analyzed the δ18O P and P concentrations in Saharan dust, desert soils and crusts. • Biological processes in crusts affect the δ18O P of dust from desert origin slightly. • δ18O P can help distinguish between desert dust and other main atmospheric P sources. [ABSTRACT FROM AUTHOR]