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Biocrusts (biological soil crusts) cover open spaces between vascular plants in most arid and semi-arid areas. Information on effects of biocrusts on seedling growth is controversial, and there is little information on their effects on plant growth and physiology. We examined impacts of biocrusts on growth and physiological characteristics of three habitat-typical plants, Erodium oxyrhynchum, Alyssum linifolium and Hyalea pulchella, growing in the Gurbantunggut Desert, northwest China. The influence of biocrusts on plant biomass, leaf area, leaf relative water content, photosynthesis, maximum quantum efficiency of PSII (Fv/Fm), chlorophyll, osmotic solutes (soluble sugars, protein, proline) and antioxidant enzymes (superoxide dismutase, catalase, peroxidase) was investigated on sites with or without biocrust cover. Biomass, leaf area, leaf water content, photosynthesis, Fv/Fm and chlorophyll content in crusted soils were higher than in uncrusted soils during early growth and lower later in the growth period. Soluble sugars, proline and antioxidant enzyme activity were always higher in crusted than in uncrusted soils, while soluble protein content was always lower. These findings indicate that biocrusts have different effects on these three ephemeral species during growth in this desert, primarily via effects on soil moisture, and possibly on soil nutrients. The influence of biocrusts changes during plant development: in early plant growth, biocrusts had either positive or no effect on growth and physiological parameters. However, biocrusts tended to negatively influence plants during later growth. Our results provide insights to explain why previous studies have found different effects of biocrusts on vascular plant growth. [ABSTRACT FROM AUTHOR]

Aims: In biological soil crusts (biocrusts) in which Diploschistes diacapsis (Ach.) Lumbsch is the predominant lichen (DIPLOS biocrusts), metabolic activity increases in response to wetting, and hot water-soluble components that react to Folin-Ciocalteu reagent are consumed during the mineralization process. We aimed to determine the types of compounds that contribute to the high rates of respiration. Methods: Aliquots of aqueous extracts (80 °C, 24 h) obtained from DIPLOS biocrusts incubated for 10 days in the dark, at 25 °C and at different levels of moisture (M1, 9.6 %; M2, 26 %; M3, 52 % and M4, 78 %, expressed as the percentage of water retained at field capacity), were analyzed by HPLC and LC/ESI/MS/MS. Results: The intensity of the peaks in HPLC chromatograms decreased as the moisture level increased, and LC/ESI/MS/MS analysis revealed that the compounds are mainly diphenols (or very small polymers of these) and products derived from these via the metapathway of phenol metabolism. A mycosporine-like product, which is stable at low moisture levels, but metabolized at high moisture levels, was also detected. Conclusions: DIPLOS biocrusts display high oxidative enzymatic activity that is capable of degrading phenols and that is probably associated with non-lichenized free living fungi proliferating at high moisture levels. The high rates of respiration associated with high humidity, together with the metabolism of compounds like mycosporines (with key functions in providing protection against UV radiation), may lead to structural collapse of the biocrusts under such conditions. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (biocrusts) are ubiquitous in drylands globally. Lichens and mosses are essential biocrust components and provide a variety of ecosystem services, making their conservation and management of interest. Accordingly, understanding what factors are correlated with their distribution is important to land managers. We hypothesized that cover would be related to geologic and pedologic factors. We sampled 32 sites throughout the eastern Mojave Desert, stratifying by parent material and the age of the geomorphic surfaces. The cover of lichens and mosses on ‘available ground’ (L + Mav; available ground excludes ground covered by rocks or plant stems) was higher on limestone and quartzite-derived soils than granite-derived soils. Cover was also higher on moderately younger-aged geomorphic surfaces (Qya2, Qya3, Qya4) and cutbanks than on very young (Qya1), older-aged surfaces (Qia1, Qia2), or soils associated with coppice mounds or animal burrowing under Larrea tridentata. When all sites and parent materials were combined, soil texture was the most important factor predicting the occurrence of L + Mav, with cover positively associated with higher silt, very fine sand, and fine sand fractions and negatively associated with the very coarse sand fraction. When parent materials were examined separately, nutrients such as available potassium, iron, and calcium became the most important predictors of L + Mav cover. [Copyright &y& Elsevier]

Biological soil crusts (BSCs) formed by different combinations of photosynthetic algae, cyanobacteria, lichens and mosses are well-developed in the Gurbantunggut Desert of northwestern China. To investigate the different responses of BSCs to environmental factors, the diurnal variations of chlorophyll fluorescence and CO exchange of BSCs in different successional stages were measured following artificial rehydration in the field. Results showed that the maximum potential quantum efficiency of PSII ( F/ F), the actual PSII efficiency (Φ) and the relative rate of electron transport as well as net photosynthesis of the different successional BSCs varied similarly and changed markedly with diurnal fluctuations in light and temperature. Further analyses indicated that CO exchange and photosynthetic pigment content of chlorophyll (Chl) a, Chl b and carotenoids increased with the developmental level of BSCs, from cyanobacterial crust to lichen crust to moss crust. The differences in responses of BSCs to environmental factors and photosynthetic pigment content may be partially attributed to differences in species composition and morphological characteristics of the various BSCs. Overall, moss crust is better adapted to a wide range of irradiance and higher temperatures than lichen and cyanobacterial crusts. Therefore, BSCs in a later successional stage are expected to play a more important role in desertification control than those of the earlier stages. [ABSTRACT FROM AUTHOR]

Abstract: In the revegetation region of Shapotou (at the southeastern edge of Tengger Desert), biological soil crusts (BSCs) generally develop and succeed from cyanobacterial soil crusts (CSCs) to lichen soil crusts (LSCs). Based on the different dominant lichens on crust surface, LSCs were further divided into cyanolichen soil crusts (CLSCs) and green algae lichen soil crusts (GLSCs). In this study, the microstructures and photosynthetic diurnal changes in both CLSCs and GLSCs were investigated using the microscopic observation and chlorophyll fluorescence techniques. The results showed the different types of LSCs have different surface morphological characteristics and inner structures due to the different biological compositions. Compared with the CLSCs, GLSCs had a higher photosynthetic efficiency, including the maximum photosynthetic efficiency (Fv/Fm) and effective photosynthetic efficiency (Φ PSII), which in the final analysis was considered to be closely correlated with the different photosynthetic characteristics between different photobiont types (green algae and cyanobacteria). In addition, similar to CSCs, a midday depression of photosynthetic efficiency was detected in LSCs, although the depression extents were different in different types of LSCs. In conclusion, the occurrence of midday depression of photosynthetic efficiency might be a stress effect and also an adaptation strategy of LSCs to adversity, especially the high light intensity and temperature at noon. [Copyright &y& Elsevier]

Abstract: Invasion by the exotic annual grass Bromus tectorum has increased the cover and connectivity of fine litter in the sagebrush steppes of western North America. This litter tends to cover biological soil crusts, which could affect their metabolism and growth. To investigate this possible phenomenon, biological soil crusts dominated by either the moss Bryum argenteum or the lichen Diploschistes muscorum were covered with B. tectorum litter (litter treatment) or left uncovered (control treatment) and exposed to natural field conditions. After periods of five and ten months, we removed the litter and compared the photosynthetic performance of biological soil crusts from the two treatments. Litter induced photosynthetic changes in our samples. In both B. argenteum and D. muscorum, biological soil crusts that had been covered with litter for ten months had lower rates of gross photosynthesis and lower chlorophyll content than control samples. Similarly in both biological soil crust types, litter reduced the rate of dark respiration. For D. muscorum, the reduction in dark respiration fully compensated for the decrease in gross photosynthesis, resulting in similar values of net photosynthesis in the two treatments. In contrast, for B. argenteum, net photosynthesis was four-times greater in the control than the litter treatment. Also under litter cover, D. muscorum showed three common adaptations to shade conditions: a decrease in the light compensation point, in the light intensity needed to achieve 95% of maximal net photosynthesis, and in the chlorophyll a/b ratio. None of these changes was apparent in B. argenteum. Overall, our results indicate that photosynthetic responses to the presence of litter varied among species of the crust biota and that the litter can reduce the photosynthetic capacity of biological soil crusts. These results help to explain field observations of decreases in biological soil crust cover and changes in biological soil crust composition with increases in litter cover, and suggest that the landscape-wide invasion by B. tectorum may have substantial effects on biological soil crust performance and therefore their capacity to function in semiarid shrublands. [Copyright &y& Elsevier]

Abstract: Biological soil crusts of arid and semiarid regions are one of the least explored habitats with respect to the diversity of their fungal communities and the Arabian deserts, in particular, remains mycologically poorly investigated. Here, we investigate the diversity of free-living and lichen-forming fungal communities associated with crusts at two locations in Oman, using intensive cultivation and pyrosequencing, and their role in improving soil stability and hydrology. A total of 226 fungal isolates were recovered and phylogenetic analysis placed 98% of the isolates within the Ascomycota phylum, most of which belonged to Dothideomycetes class and Pleosporales order. The isolates were phylogenetically affiliated to 101 different species within 44 different genera with >55% of the total isolates belonging to Alternaria, Aspergillus, Cladosporium, Cochliobolus, Fusarium, Myrothecium, Phoma and Ulocladium. Using pyrosequencing, a total of 26,998 sequence reads were obtained with Ascomycota, Basidiomycota and Chytridiomycota encompassing >96% of the total sequences. In cyanobacterial crusts, between 67.2 and 70.6% of the total fungal sequences belonged to the classes Dothideomycetes and Eurotiomycetes with the dominance of yeast-like fungi of the genera Sarcinomyces and Aureobasidium. On the other hand, the sequences obtained from the lichen crusts mainly belonged to the classes Lichinomycetes, Lecanoromycetes and Eurotiomycetes. Among the identified lichens were Placidium lacinulatum, Psora decipiens, Peccania fontqueriana, Stromatella bermudana, Verrucaria chiloensis, Pecania arizonica, Lempholemma polyanthes and Lichinella cribellifera. Although detected fungi confirmed earlier trends in fungal diversity in other deserts, quite a number of isolates and sequences representing novel taxa were recovered. The presence of lichen in crusts improved their resistance to erosion and increased their water holding capacity. We conclude that desert crusts of Oman harbor a large diversity of fungal communities that varies with crust type and desert ecoregions, and the presence of lichens in these crusts improves soil characteristics. [Copyright &y& Elsevier]

Biological soil crusts (BSCs) are key biotic components of dryland ecosystems worldwide that control many functional processes, including carbon and nitrogen cycling, soil stabilization and infiltration. Regardless of their ecological importance and prevalence in drylands, very few studies have explicitly evaluated how climate change will affect the structure and composition of BSCs, and the functioning of their constituents. Using a manipulative experiment conducted over 3 years in a semi-arid site from central Spain, we evaluated how the composition, structure and performance of lichen-dominated BSCs respond to a 2.4°C increase in temperature, and to an approximately 30 per cent reduction of total annual rainfall. In areas with well-developed BSCs, warming promoted a significant decrease in the richness and diversity of the whole BSC community. This was accompanied by important compositional changes, as the cover of lichens suffered a substantial decrease with warming (from 70 to 40% on average), while that of mosses increased slightly (from 0.3 to 7% on average). The physiological performance of the BSC community, evaluated using chlorophyll fluorescence, increased with warming during the first year of the experiment, but did not respond to rainfall reduction. Our results indicate that ongoing climate change will strongly affect the diversity and composition of BSC communities, as well as their recovery after disturbances. The expected changes in richness and composition under warming could reduce or even reverse the positive effects of BSCs on important soil processes. Thus, these changes are likely to promote an overall reduction in ecosystem processes that sustain and control nutrient cycling, soil stabilization and water dynamics. [ABSTRACT FROM AUTHOR]

Acarospora dissecta (Bolivia) and Sarcogyne brunnea (Bolivia, Ecuador) are described as new to science. Acarospora trachyticola, a common effigurate species in Peru, is revised and reported as new for Argentina, Bolivia and Venezuela. Acarospora brasiliensis is considered as a later synonym of A. lorentzii, which is reported new for Peru. Sarcogyne terrena is revised. Silobia smaragdula is verified as occurring in Chile. Polysporina urceolata is reported new to South America from Bolivia. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) greatly influence the N cycle of semi-arid ecosystems, as some organisms forming them are able to fix atmospheric N. However, BSCs are not always taken into account when studying biotic controls on N cycling and transformations. Our main objective was to understand how BSCs modulate the availability of N in a semi-arid Mediterranean ecosystem dominated by the tussock grass Stipa tenacissima. We selected the six most frequent soil cover types in the study area: S. tenacissima tussocks (ST), Retama sphaerocarpa shrubs (RS), and open areas with very low (BS), low (LC) medium (MC) and high (HC) cover of well developed and lichen-dominated BSCs. The temporal dynamics of available N dynamics followed changes in soil moisture. Available NH-N did not differ between microsites, while available NO-N was substantially higher in the RS than in any other microsite. No significant differences in the amount of available NO-N were found between ST and BS microsites, but these microsites had more NO-N than those dominated by BSCs (LC, MC and HC). Our results suggest that BSCs may be inhibiting nitrification, and highlight the importance of this biotic community as a modulator of the availability of N in semi-arid ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Despite advancements in our knowledge on the importance of biological soil crusts (BSC) in arid and semiarid environments, little is known on the effects of specific crust organisms on vascular plant seed emergence. We conducted a growth chamber experiment to evaluate the effects of two BSC-forming lichens (Squamarina lentigera and Diploschistes diacapsis) on the emergence of three specialist vascular plants from gypsum Mediterranean habitats (Campanula fastigiata, Reseda stricta and Helianthemum squamatum). The design of the experiment included three disturbance levels (intact, disturbed and removed) and two sterilization levels (live vs. autoclaved) of BSC-forming lichens. Specifically, we evaluated three hypotheses: (i) lichens will reduce the emergence of vascular plants, (ii) the magnitude of the negative effect of lichens on emergence will be species-specific, and (iii) the two species of lichens evaluated will exert differential effects on seed emergence. Emergence in the presence of lichens was lower than that obtained in tests conducted under optimum lab conditions (reduction of 50%). The effects of crust disturbance and sterilization on seed emergence were species-specific, and also varied with the lichen species serving as substrate. When germinated with Squamarina, a disturbance×sterilization interaction was found in Campanula. Disturbance increased and reduced the emergence of this species when the lichen was dead and alive, respectively. When Helianthemum was sown on Squamarina and Diploschistes, disturbance reduced and increased, respectively, the emergence of this species. The emergence of Reseda was not affected by any treatment when sown on Diploschistes, but disturbance reduced it when shown on Squamarina. Our results highlight the importance of species-specific interactions between vascular plants and BSC-forming soil lichens. The potential mechanisms underlying these interactions are discussed. [Copyright &y& Elsevier]

Abstract: Soil crust lichens can be the dominant vegetation in arid lands, yet their importance as habitat to secondary producers is relatively unknown. This study examines the distribution of arthropod communities in the northern Namib Desert to evaluate whether a lichen-rich area is more or less productive than adjacent habitats in terms of the consumers each supports. Arthropods are diverse and highly endemic in the Namib Desert and lichens dominate this desert''s extensive gravel plains. We sampled lichen-rich, dwarf shrub, and unvegetated sites and found distinct arthropod assemblages in the lichen-dominated sites, including species unique to lichen sites. Arthropod assemblages in two of the lichen sites were similar to those found in the dwarf shrub site. In a canonical correspondence analysis, crustose lichens and overall lichen cover were key in driving the variance in arthropod assemblages within the lichen sites. Furthermore, lichen morphotypes, overall lichen cover and species richness, were significantly correlated with the representation of arthropod subgroups and arthropod species richness. These findings provide evidence that lichen-dominated soil crusts in the Namib Desert are important supporters of secondary production, warranting more in-depth studies into the ecology and conservation of this lichen-rich habitat in warm deserts. [Copyright &y& Elsevier]

Biological soil crusts composed of cyanobacteria, green algae, bryophytes, and lichens colonize soils in arid and semiarid ecosystems worldwide and are responsible for significant N input to the soils of these ecosystems. Soil crusts also colonize active sand dunes in more humid regions, but studies of structure and function of such sand dune crusts are lacking. We identified the cyanobacterial, algal, and bryophytic constituents and N production and leachates of biological soil crusts that colonize beach dunes at the Indiana Dunes National Lakeshore along southern Lake Michigan in Indiana, USA. To determine the role of these crusts in this system, we conducted a greenhouse experiment in which intact soil cores with biological crusts were subjected to artificial rainfall over a full growing season. The volume and N content of leachate from the cores were quantified in relation to degree of crust development, taxonomic composition, rainfall volume and intensity, light intensity, and the presence of plant litter. Net N throughput significantly exceeded N inputs to cores in rainwater. Net N outputs from crusts to subsurface soil ranged from 0. 01 to 0.19 g NH-N m−2 yr−1 and 0.01 to 0.61 g NON m−2 yr−1. Thus, total inorganic N inputs associated with biological soil crusts ranged from 0.02 g N m−2 yr−1 to 0.8 g N m−2 yr−1. High volume (≥2 cm) rainfall resulted in more N leaching than low volume events, and plant litter added over the surface of crusted soil cores significantly increased the amount of N in leachate. Exploratory path analysis revealed direct and indirect linkages among environmental factors, crust development, and crust composition in regulating the throughput of H2O and N from these intact soil cores. Biological soil crusts at this site, combined with other properties of the soil surface, substantially increase N inputs to this water- and nutrient-limited sand dune ecosystem. [ABSTRACT FROM AUTHOR]