Biological Soil Crusts

Moss-soil lichens crust at reclaimed post-mining site, Brandenburg, GermanyBiocrusts on reclaimed post-mining site, Lower Lausatia, GermanyCyanobacterial biocrust on desert dunes, Succulent Karoo, South AfricaInitial biocrust on reclaimed post mining-site, Lower Luasatia GermanyCyanobacterial biocrust on desert dunes, Nizzana, Negev, IsraelInitial green-algae soil crust on temperate sand dunes, Brandenburg, GermanySoil lichens crust, Karoo, South AfricaSoil lichens crust, Northern Negev, IsraelSoil lichens crust at reclaimed post-mining site, Brandenburg, GermanyCyanobacterial crust on desert dunes, Northern ChinaMoss biocrust at reclaimed post-mining site, Brandenburg, Germany

In many ecosystems of the world biological soil crusts play an important role for ecosystem processes. These biological crusts (also called microbiotic, microphytic or cryptogamic crusts) are assemblages of cyanobacteria, green algae, mosses, liverworts, fungi and/or lichens. BSC are highly stress tolerant under extreme environmental conditions and therefore widespread in many ecosystems from the deserts to polar regions. 

Biocrusts influencing the ecosysten processes: they decrease infiltration rates and, thus, run-off could be observed even in a sandy area when covered by a biological crust. In addition to the influence on the ecohydrological conditions, the biological crust also stabilises the topsoil, reduces soil erosion, and enhances the nitrogen pools by nitrogen fixation. The understanding of pattern formations and interactions with biogeochemical and biotic processes are important for ecological theory and for applications in restoration ecology and combating desertification. Currently we investigate the spatial and temperal variance of photosynthesis of biocrusts from the temperate zone using chlorophyll fuorescence and NDVI measurements. 

  • Photosynthetic characteristics and their spatial variance on biological soil crusts covering initial soils of post-mining sites in Lower Lusatia, NE Germany
crust ecophysiology-0011

Following surface disturbance, quaternary sands are the basic substrate for soil development in the Lusatian reclamation area. These substrates mostly contain low organic matter and, hence, are nutrient poor. Accumulation of soil carbon is an important factor for ecosystem development, where biological soil crusts initially influence soil processes and promote ecosystem succession. The compositional structures of biological soil crusts at various developmental stages and their photosynthetic properties were investigated on two former open-cast lignite sites, currently under reclamation, an artificial sand dune in Welzow Süd, and a forest plantation in Schlabendorf Süd (Brandenburg, Germany). As development of biological soil crusts progressed, their contents of organic carbon and total chlorophyll increased. The ratio of these parameters, however, varied with the relative contribution of lichens and mosses in particular. Also maximum photochemical efficiency, net photosynthesis and respiration increased with crustal development. An additional evaluation of NDVI and chlorophyll fluorescence images showed that especially moss-dominated biocrusts had higher photosynthetic capacity compared to green algae-dominated biocrusts or soil lichens, so the photosynthetic capacity showed to be highly species-specific. The ratio of gross photosynthesis to respiration indicated a higher ecological efficiency of biocrusts dominated by green algae than of biocrusts. The occurrence of soil lichens reduced net CO2 fixation and increased CO2 release due to the enhanced mycobiontic respiration. During crustal succession, the rise of photosynthesis-related parameters is not necessarily linear as a result of the highly heterogenic distribution of the different crustal organisms between biocrusts of similar developmental stages as well as between those growing at the two study sites. Therefore, the evaluation of relevant ecophysiological parameters highlighted that not all biocrust-forming organisms similarly contribute to the ecophysiological behavior of biological soil crusts. Nevertheless, the occurrence of the biological soil crusts promoted soil formation and accumulation of soil carbon in initial soils.

Gypser, S, Herppich, W.B., Fischer, T., Lange, P., Veste, M. (2016): Photosynthetic characteristics and their spatial variance on biological soil crusts covering initial soils of post-mining sites in Lower Lusatia, NE Germany. Flora 220: 103-116.

  • Infiltration and water retention of biological soil crusts on reclaimed soils of former open-cast lignite mining sites in Brandenburg, north-east Germany
Biocrust (2)

Investigations were done on two former open-cast lignite mining sites under reclamation, an artificial sand dune in Welzow Süd, and a forest plantation in Schlabendorf Süd (Brandenburg, Germany). The aim was to associate the topsoil hydrological characteristics of green algae dominated as well as moss and soil lichen dominated biological soil crusts during crustal succession with their water retention and the repellency index on sandy soils under temperate climate and different reliefs. The investigation of the repellency index showed on the one hand an increase due to the cross-linking of sand particles by green algae which resulted in clogging of pores. On the other hand, the occurrence of moss plants led to a decrease of the repellency index due to absorption caused by bryophytes. The determination of the water retention curves showed an increase of the water holding capacity, especially in conjunction with the growth of green algae layer. The pore-related van Genuchten parameter indicates a clay-like behaviour of the developed soil crusts. Because of the inhomogeneous distribution of lichens and mosses as well as the varying thickness of green algae layers, the water retention differed between the study sites and between samples of similar developmental stages. However, similar tendencies of water retention and water repellency related to the soil crust formation were observed. Biological soil crusts should be attended after disturbances in the context of reclamation measures, because of their small-scale succession and, hence, the promotion of soil and ecosystem development.

Gypser, S., Veste, M., Fischer, T., Lange, P.  (2016): Infiltration and water retention of biological soil crusts on reclaimed soils of former open-cast lignite mining sites in Brandenburg, north-east Germany. Journal of Hydrology and Hydromechanics 64 (1): 1-11.

  • Formation of soil lichen crusts at reclaimed post-mining sites, Lower Lusatia,
    North-east Germany

Biological soil crusts were investigated at reclaimed post-mining sites near Welzow and Schlabendorf in Lower Lusatia (Brandenburg, Germany). Various development stages from initial biological soil crusts built up by green algae, to more developed soil crusts with mosses, as well as moss-soil lichen crusts, were classified. The spatial-temporal dynamics during the development resulted in a moss-lichens cover with discrete patches of pioneer organisms like green algae in between. At the study sites, 13 species of terricolous lichens were identified. The formation of the biological soil crust is important for the accumulation of soil organic matter in the first millimeters of the topsoil of these pioneer ecosystems. A correlation between cryptogamic biomass and soil carbon content were found.

Gypser, S., Veste, M., Fischer, T., Lange, P. (2015): Formation of soil lichens crusts at reclaimed post-mining sites, Lower Lusatia, North-east Germany.  Graphis Scripta 27 (1–2): 3-14.

  • Synergic hydraulic and nutritional feedback mechanisms control surface patchiness of biological soil crusts on tertiary sands at a post-mining site 

In a recultivation area located in Brandenburg, Germany, five types of biocrusts (initial BSC1, developed BSC2 and BSC3, mosses, lichens) and non-crusted mineral substrate were sampled on tertiary sand deposited in 1985 – 1986 to investigate hydrologic interactions between crust patches. Crust biomass was lowest in the non-crusted substrate, increased to the initial BSC1 and peaked in the developed BSC2, BSC3, the lichens and the mosses. Water infiltration was highest on the substrate, and decreased to BSC2, BSC1 and BSC3. Non-metric multidimensional scaling revealed that the lichens and BSC3 were associated with water soluble nutrients and with pyrite weathering products, thus representing a high nutrient low hydraulic feedback mode. The mosses and BSC2 represented a low nutrient high hydraulic feedback mode. These feedback mechanisms were considered as synergic, consisting of run-off generating (low hydraulic) and run-on receiving  (high hydraulic) BSC patches. Three scenarios for BSC succession were proposed. (1) Initial BSCs sealed the surface until they reached a successional stage (represented by BSC1) from which the development into either of the feedback modes was triggered, (2) initial heterogeneities of the mineral substrate controlled the development of the feedback mode, and (3) complex interactions between lichens and mosses occurred at later stages of system development. 

Fischer, T., Gypser, S., Subbotina, M., Veste, M., Journal of Hydrology and Hydromechanics, 2014

  • Organic matter from biological soil crusts induces the initial formation of sandy temperate soils
BSC Lugteich

Different development stages of algae-dominated and moss-dominated biological soil crusts (BSCs) were sampled on a natural sand dune (< 17 years old) and on an experimental sand dune (< 8 years old) along a catena, including gradients of vegetation cover, location on the slope, as well as composition and thickness of BSC organisms in northeastern Germany. The accumulation of BSC-derived organic carbon (OC) was determined for bulk materials and fractions less than 63 μm. The OC composition was characterized by solid-state 13C NMR spectroscopy and the carbohydrate-C signature. 14C contents were determined to assess the origin and dynamics of OC. From the radiocarbon contents, two OC pools were differentiated: recent BSC-derived and lignite-derived “old” OC. Downward movement of OC into the underlying substrate was found only under moss-dominated BSCs at the old sand dune. BSC-derived OC was mainly composed of carbohydrate-C and, to a lesser extent, alkyl C and N-alkyl C, with considerably higher contributions of alkyl C in the young dune, indicating differences in the composition of extracellular polymeric substances produced by the BSCs with age. This is consistent with higher proportions of water-soluble OC of moss-dominated BSCs at the old dune, which is leached in the underlying substrate and initiates soil formation. Because of the channeling effect of mosses, OC depth translocation along with suspended colloidal substances may contribute to OC accumulation in substrates.

Dümig, A., Veste, M., Hagedorn, F., Fischer, T., Lange, P., Spröte, R., Kögel-Knabner, I., Catena 122, 196–208, 2014 (more..)

  • Succession of N cycling processes in biological soil crusts on a central European inland dune. 
DSC05208 2 Kopie

Biological soil crusts (BSCs) are microbial assemblages that occur worldwide and facilitate ecosystem development by nitrogen (N) and carbon accumulation. N turnover within BSC ecosystems has been intensively studied in the past; however, shifts in the N cycle during BSC development have not been previously investigated. Our aim was to characterise N cycle development first by the abundance of the corresponding functional genes (in brackets) and second by potential enzyme activities; we focussed on the four processes: N fixation (nifH), mineralisation as proteolysis and chitinolysis (chiA), nitrification (amoA) and denitrification (nosZ). We sampled from four phases of BSC development and from a reference located in the rooting zone of Corynephorus canescens, on an inland dune in Germany. BSC development was associated with increasing amounts of chlorophyll, organic carbon and N. Potential activities increased and were highest in developed BSCs. Similarly, the abundance of functional genes increased. We propose and discuss three stages of N process succession. First, the heterotrophic stage (mobile sand without BSCs) is dominated by mineralisation activity. Second, during the transition stage (initial BSCs), N accumulates, and potential nitrification and denitrification activity increases. Third, the developed stage (established BSCs and reference) is characterised by the dominance of nitrification.

Brankatschk, R., Fischer, T., Veste, M., Zeyer, J. FEMS Microbiology Ecology 83 (1),149-160, 2013. (more…)

  • Water repellency and pore clogging at early successional stages of microbiotic crusts on inland dunes, Brandenburg, NE Germany

Biological soil crusts play a key role for hydrological processes in many open landscapes. They seal the topsoil and generate surface run-off. Utilization of the mineral substrate at early stages of microbiotic crusts was investigated using scanning electron microscopy (SEM), water repellency indices were measured using the ethanol/water microinfiltrometer method, and steady state water flow was determined on the dry crusts and after 300, 600, 1200 and 1800 s of wetting, thus allowing to follow pore clogging through swelling of extracellular polymeric substances (EPS). It was found that water repellency increases with initial crust development where filamentous cyanobacteria and filamentous green algae were dominating, but decreases as coccal algae, bryophytes and fungi associated with bryophytes emerged. Swelling of EPS took place immediately after wetting, and its influence on steady state water flow was most pronounced when filamentous cyanobacteria and algae partially filled in the matrix pores and enmeshed sand grains, still leaving micropore channels available for free water infiltration, but prior to appearance of coccal algae, bryophytes and associated fungi which formed a dense cover on the surface. It was concluded that a new phase of crust succession was accompanied by easier wettability but slower infiltration. Transition from hydrophobicity to pore clogging as ruling mechanisms causing water run-off may occur during wetting of individual biological crusts, but also during crust succession over time.

Fischer, Veste, M., Wiehe, W., Lange, P., Catena 80 (1), 47-52, 2010. (more)

  • Microstructure and hydraulic properties of biological soil crusts on sand dunes: a comparison between arid and temperate climates
Biological soil crust sand dunes Lieberose, Brandenburg, NE Germany

We studied the relationships between crust microstructure, infiltration and water holding capacity under arid and temperate conditions (Factor A: Climate) on biological soil crusts (BSCs) sampled along a~catena on mobile sand dunes (Factor B: Catena). The arid study site was located near Nizzana, Israel (precipitation: 86 mm a−1, PET: ~2500 mm a−1) and the temperate site near Lieberose, Germany (precipitation: 569 mm a−1, PET: ~780 mm a−1). BSCs were sampled near the dune crest, at the centre of the dune slope and at the dune base at each site. Scanning electron microscopy (SEM) was used to characterize BSC morphology and microstructure. Infiltration was determined using microinfiltrometry under controlled moisture conditions in the lab. Water holding capacities were determined after water saturation of the dry BSCs. Wettability of the crusts was characterized using a "repellency index", which was calculated from water and ethanol sorptivities. Irrespective of the climate, an accumulation of fine particles in the BSCs was found, increasing along the catena from dune crest to dune base. Texture was finer and water holding capacities of the underlying substrate were higher at the arid site, whereas surface wettability was reduced at the temperate site. At both sites, BSCs caused extra water holding capacity compared to the substrate. Infiltration rates decreased along the catena and were generally lower at the dune slope and base of the arid site. A mechanism of crust stabilization is proposed where BSCs benefit from increased texture and biomass mediated water supply, and where the water supply to higher plants was limited due to alteration of physico-chemical surface properties under temperate conditions.

Fischer, T., Yair, A., Veste, M.,  Biogeosciences Discuss., 9, 12711-12734, 2012. (more…)

  • Biological topsoil crusts at early successional stages on Quaternary substrates dumped by mining in Brandenburg, NE Germany

The influence of biological soil crusts in natural ecosystems on structures and processes is well investigated. However, in South-Brandenburg (Germany), it is possible to study the development of biological soil crusts (BSC) during initial ecosystem genesis on two artificial water catchments with well-known ages and under differing starting conditions. The two experimental sites are located in the recultivation area of the lignite open-cast mining district of southern Brandenburg with a distance of approximately 1 km between them. Two different topographies were constructed at the experimental sites: the experimental plot at the catchment Neuer Lugteich was shaped like a dune, whereas the artificial water catchment Hühnerwasser was modelled as an inclined slope. The catchment Neuer Lugteich is four years older than Hühnerwasser. The original substrate at Neuer Lugteich is more sandy and carbonate-free compared to the original substrate dumped at Hühnerwasser. At both sites geomorphological differentiation and crust development were compared and the importance of substrate-dependent water availability and crust type clarified. Once settled, the crusts influenced the water regime of the soils by delaying infiltration through enhanced water repellency, and by limiting water infiltration. Chlorophyll analysis revealed that all crusts were at early stages of development. At Neuer Lugteich, the establishment of the biological soil crusts was closely associated with the vegetation succession, whereas no clear succession of the crusts could be observed at Hühnerwasser. The mosaic-like pattern of the biological soils crusts is associated with the distribution of fine-grained material here.

Spröte, R.,Fischer, T., Veste, M., Raab, T., Wiehe, W., Lange, P., Bens, O., Hüttl, R.F.,Géomorphologie: relief, processus, environnement 4/2010: 359-370.

  • Initial pedogenesis in a topsoil crust 3 years after construction of an artificial catchment in Brandenburg, NE Germany

Cyanobacteria and green algae present in biological soil crusts are able to colonize mineral substrates even under extreme environmental conditions. As pioneer organisms, they play a key role during the first phases of habitat colonization. A characteristic crust was sampled 3 years after installation of the artificial water catchment “Chicken creek”, thus representing an early successional stage of ecosystem development. Mean annual rainfall and temperature were 559 mm and 9.3°C, respectively. We combined scanning electron microscopy (SEM/EDX) and infrared (FTIR) microscopy to study the contact zone of algal and cyanobacterial mucilage with soil minerals in an undisturbed biological soil crust and in the subjacent sandy substrate. The crust was characterized by an approximately 50 μm thick surface layer, where microorganisms resided and where mineral deposition was trapped, and by an approximately 2.5 mm thick lower crust where mineral particles were stabilized by organo-mineral structures. SEM/EDX microscopy was used to determine the spatial distribution of elements, organic compounds and minerals were identified using FTIR microscopy and X-ray diffraction (XRD). The concentration of organic carbon in the crust was about twice as much as in the parent material. Depletion of Fe, Al and Mn in the lower crust and in the subjacent 5 mm compared to the geological substrate was observed. This could be interpreted as the initial phase of podzolization. Existence of bridging structures between mineral particles of the lower crust, containing phyllosilicates, Fe compounds and organic matter (OM), may indicate the formation of organo-mineral associations. pH decreased from 8.1 in the original substrate to 5.1 on the crust surface 3 years after construction, pointing to rapid weathering of carbonates. Weathering of silicates could not be detected.

Fischer, T., Veste, M., Schaaf, W., Bens, O., Dümig, A., Kögel-Knabner, I, Wiehe, W.,  Hüttl, R.F., Biogeochemistry 101, 165-176, 2010. (more…)

  • Biogeography and ecophysiological adaptations of bi-polar lichens

Aspects of biogeographical relation and ecophysiological adaptation of bi- polar lichens, based on more than 200.000 distributional data sets as well as eco- physiological measurements of Antarctic lichens, are discussed. For the first time calculated values of similarity of the Antarctic region with all other continents are presented. The isolated position of the Antarctic lichen flora is confirmed. Sørensen indices are visualized by diagrams. Antarctic lichen populations of Usnea aurantiaco- atra show low net photosynthesis rates compared to those of most species from less extreme habitats, due to low temperature, nitrogen limitation and low chlorophyll content.

Veste, M., Feuerer, T. (2008): Zur Biogeographie und ökophysiologischen Anpassung bipolarer Flechten. Abhandlungen aus dem Westfälischen Museum für Naturkunde Münster 70, Heft 3/4,  pp. 379-389

  • Vegetation pattern in arid sand dunes controlled by biological soil crusts along a climatic gradient in the Northern Negev desert
Haluza sand dunes

Vegetation cover and biomass production in drylands are largely controlled by rainfall amounts on a regional and global scale. However, soil water availability on the small-scale is influenced by hydrological processes, soil types and surface properties. In the sand dunes of the north-western Negev biological soil crusts built up by cyanobacteria, green algae, mosses and soil lichens play an important role for the ecosystem processes. They are changing the surface properties. We investigated the vegetation in response to geo-ecological parameters and biological soil crusts along a rainfall gradient from 170 mm to 78 mm. In the interdunes the vegetation cover was 26-30% and showed no significant difference along the climatic gradient. Vegetation cover on the dune crests depends on the sand mobility and decreases towards the more arid parts. The biological crusts limit infiltration and counteract on the rainfall gradient. Therefore, no differences in the vegetation cover were detected and on the mesoscale level the biomass index was negatively correlated to the annual rainfall. Sand mobility and surface stability are important parameters determining the vegetation pattern. Surface properties like crust and fine material are key factors for the hydrological processes and control water redistribution on the micro-scale and, thus, vegetation pattern.

Veste, M., Breckle, S.-W., Eggert, K., Littmann, T., Basic and Applied Dryland Research 5, 1-16, 2011. (more…)

  • Differential hydrological response of biological topsoil crusts along a rainfall gradient in a sandy arid area: Northern Negev desert, Israel

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 300 mm 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 160 mm. 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.

Yair, A., Almog, R., Veste, M., Catena 87 (3), 326-333, 2011. (more…)

  • A natural 15N approach to determine the biological fixation of atmospheric nitrogen by biological soil crusts of the Negev desert. 

Biological soil crusts are important cryptogamic communities covering the sand dunes of the north-western Negev. The biological crusts contain cyanobacteria and other free-living N2-fixing bacteria and are hence able to fix atmospheric nitrogen (N). This is why they are considered to be one of the main N input pathways into the desert ecosystem. However, up to now, in situ determinations of the N2 fixation in the field are not known to have been carried out. We examined the natural 15N method to determine the biological N2 fixation by these soil crusts under field conditions. This novel natural 15N method uses the lichen Squamarina with symbiotic green algae—which are unable to fix N2—as a reference in order to determine N2 fixation. Depending on the sampling location and year, the relative biological fixation of atmospheric nitrogen was estimated at 84–91% of the total N content of the biological soil crust. The cyanobacteria-containing soil lichen Collema had a fixation rate of about 88%. These fixation rates were used to derive an absolute atmospheric N input of 10–41 kg N ha−1 year−1. These values are reasonable results for the fixation of atmospheric N2 by the biological crusts and cyanolichens and are in agreement with other comparable lab investigations. As far as we are aware, the results presented are the first to have been obtained from in situ field measurements, albeit only one location of the Negev with a small number of samples was investigated.

Russow, R., Veste, M., Böhm, F., Rapid Communication in Mass Spectrometry 19 (23): 3451-3456, 2005. (more…) 

  • Using the natural 15N-abundance to assess the major nitrogen inputs into the sand dune area of the north-western Negev Desert (Israel)

The variation of the natural 15N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to usethis approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system:

i. Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N2-fixing vascular plants (e.g. the shrub Retama raetam);

ii. Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition.

Samples were taken from selected environmental compartments such as biological crusts, sand underneath these crusts (down to a depth of 90 cm), N2 fixing and non-N2-fixing plants, atmospheric bulk deposition as well as soil from arable land north of the sandy area in three field campaigns in March 1998, 1999 and 2000. The d15N values measured were in the following ranges: grass 2.5‰ to þ1.5‰; R. reatam: þ0.5‰ to þ4.5‰; non-N2-fixing shrubs þ1‰ to þ7‰; sand beneath the biological crusts þ4‰ to þ20‰ (soil depth 2–90 cm); and arable land to the north up to 10‰. Thus, the natural 15N abundance of the different N pools varies significantly. Accordingly, it should be feasible to assess different input pathways from the various 15N abundances of nitrogen. For example, the biological N fixation rates of the Fabaceae shrub R. reatam from the 15N abundances measured were calculated to be 46–86% of biomass N derived from the atmosphere. The biological crusts themselves generally show slight negative 15N values (3‰ to  0.5‰), which can be explained by biological N fixation. However, areas with a high share of lichens, which are unable to fix atmospheric nitrogen, show very negative values down to 10‰. The atmospheric N bulk deposition, which amounts to 1.9–3.8 kgN=ha yr, has a 15N abundance between 4.4‰ and 11.6‰ and is likely to be caused by dust from the arable land to the north. Thus, it cannot be responsible for the very negative values of lichens measured either. There must be an additional N input from the atmosphere with negative d15N values, e.g. gaseous N forms (NOx, NH3). To explain these conflicting findings, detailed information is still needed on the wet, particulate and gaseous atmospheric

deposition of nitrogen.

Russow, R., Veste, M., Littmann, T., Isotopes in Environmental and Health Studies 40, 57-67, 2004. (more…

  • Dewfall and its geo-ecological implication for biological surface crusts in desert sand dunes (north-western Negev, Israel).

Dew is an important water source for biological soil crusts and lichens in arid and semi-arid ecosystems. These crusts influencing the ecosystem processes resulting in a patchy ecotope and vegetation distribution. Microclimatic boundary conditions for nocturnal wetting were determinate. Maximum activity of crust is reached a few hours later after dewfall starts when cumulative dewfall exceeds 0.1 mm at dew point temperature differences around 0 K. Different microclimatic approaches were applied to estimated dewfall amounts in sand dunes of the north-western Negev. The annual dewfall amounts obtained from the zeroplane model was 26 mm a-1 and from the load cell 33 mm a-1, whereas other models mostly overestimated the dew amounts. However, spatial differences in shading after sunrise could explain the crust pattern in the sand dunes.

Veste, M., Littmann, T., Journal of Arid Land Studies 16(3), 139-147. 2006. (more…)

  • Microclimatic boundary conditions for activity of soil lichen crusts in sand dunes of the north-western Negev desert, Israel 
Fulgensia fulgens Negev, Israel

Photosynthetic activity of soil crust lichens was thoroughly investigated. Its interrelations with microclimatic boundary conditions was measured during two field experiments in the central part of the sand dune field in the north-western Negev Desert. After nocturnal rainfall the lichens were active well until noon when they dried out finally. However, over most of the year dewfall seems to be the primary controlling factor for activation as in other lichen communities. The microclimatic conditions for activity were determined in detail. It was found that after sunset terrestrial radiation leads to a progressive development of a stable air layer above ground accompanied by decreasing temperatures and wind speed. Well before midnight dewpoint temperature differences drop below 1.0 K  and leaf wetness sensors indicate the formation of dew. It is exactly in this situation when lichen activity starts. Maximum activity, however, is reached a few hours later when cumulative dewfall exceeds 0.1 mm at dewpoint temperature differences around 0 K. In nights with advective labilization and subsequent dewfall evaporation, no lichen activity was observed. Even a heavy foggy night did not lead to any activity at the soil surface.

Veste, M., Littmann, T., Friedrich, H., Breckle, S.-W., Flora 196 (6), 465-476, 2001. (more…)

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