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Soil erosion is a significant environmental issue worldwide, particularly in island regions where land resources are exceedingly scarce. Biological soil crusts play a crucial role in mitigating soil erosion, yet the precise effect and mechanism of biological soil crusts against erosion remain ambiguous. In this study, biological soil crusts at various developmental stages from a tropical coral island in the South China Sea were chosen to investigate the role of carbonic anhydrase in mitigating erosion. A cohesive strength meter, real-time quantitative PCR, and 16S rRNA gene high-throughput sequencing were employed to assess variations in soil antiscouribility as well as bacterial abundance and composition during the formation and development of biological soil crusts. Scanning electron microscopy was utilized to detect carbonates induced by bacterial carbonic anhydrase and elucidate their role in the solidification of sand particles. The findings indicate that the formation and development of biological soil crusts significantly enhance anti-scouribility. Comparison to those of bare coral sand, the shear stress increased from 0.35 to 1.11 N/m2 in the dark biocrusts. Moreover, significantly elevated carbonic anhydrase activity was observed in biological soil crusts, demonstrating a positive correlation with antiscouribility. In addition, there was a significant increase in bacterial abundance within the biological soil crusts. The enrichment of Cyanobacteriales and Chloroflexales potentially contributed to the increased carbonic anhydrase activity and antiscouribility. Furthermore, three cyanobacterial strains with carbonic anhydrase activity were isolated from biological soil crusts and subsequently confirmed to enhance sand solidification through microbial carbonate precipitation. This study presents initial evidence for the role of microbial carbonic anhydrase in enhancing the antiscouribility of biological soil crusts during their formation and development. These findings offer novel insights into the functional and mechanistic dimensions underlying the mitigation of soil erosion facilitated by biological soil crusts, which are valuable for implementing sustainable biorestoration and environmental management technologies to prevent soil erosion. [Display omitted] • Antiscourability and carbonic anhydrase activity enhanced during the formation and development of biological soil crusts. • Antiscourability was positive correlated with carbonic anhydrase activity. • Cyanobacteriales and Chloroflexales contribute to the augmentation of carbonic anhydrase activity. • Carbonic anhydrase-induced carbonates enhanced soil shear strength in biological soil crusts. [ABSTRACT FROM AUTHOR]

Biocrusts are soil surface assemblages of lichens, bacteria, fungi, and bryophytes that support key ecosystem processes in alpine environments. Their role in carbon and nitrogen cycling is critical to soil pedogenesis. Establishment of biocrusts after disturbance events is an important first step in restoring ecosystem function. However, our understanding of active restoration of alpine biocrusts, as well as how environmental factors affect ecosystem processes associated with early succession, is poor. In a field experiment at two alpine sites (a xeric and a mesic site), we monitored microclimatic conditions and assessed function of mature biocrusts. We also examined the influence of inoculation with mature biocrusts and fertilization on the recovery of biocrusts in disturbed alpine soils. Biocrust cover and soil surface nitrogen fixation were enhanced by inoculation after 12 weeks at the mesic site. However, at the xeric site biocrust cover increased while nitrogen fixation declined. Restoration of dry and cold alpine environments presents many challenges and recovery of ecosystem services may require additional restoration techniques and longer timelines. Improved understanding of the community composition of alpine biocrusts and their developmental trajectories over time will assist with effectively using biocrusts to promote recovery of ecosystem processes in disturbed alpine environments. [ABSTRACT FROM AUTHOR]

With the continuing consumption of resources and increasingly prominent environmental issues, microalgal resource utilization has received extensive attention. In this study, based on the microalgal investigation in desert biological soil crusts (BSCs) using pyrosequencing technology, the cultivated crust microalgae were further isolated in order to obtain high quality microalgae for resource utilization. The results showed that with crust development and succession, microalgal diversity gradually decreased, including the number of operational taxonomic units (OTUs) and genus, although Microcoleus always was the dominant genera. Pyrosequencing obtained 630 OTUs of cyanobacteria, 25 OTUs of green algae and 9 OTUs of diatom; however, part of cultivated microalgae still could not yet be detected due to the DNA extraction preferences and errors caused by PCR amplification. After isolation, four strains were purified and cultivated, including two filamentous cyanobacteria Microcoleus vaginatus BSC-06 and Scytonema javanicum BSC-39, and two unicellular green algae Chlorella sp. BSC-24 and Monoraphidium dybowskii BSC-81. The two green algae grew fast (>250 mg L -1  d -1 ), and achieved high lipid productivity up to 75–85 mg L -1  d -1 , with lipid content of 28.7–39.0%, thus was considered as promising feedstock for biodiesel production. In addition, the two crust cyanobacteria could be used to construct artificial cyanobacterial soil crusts in desertification control, although their biomass accumulation was not as high as that in the green algae. Ultimately, combining biodiesel production with desertification control would not only improve desert environments, but also provide ideal places for the local microalgal resource exploitation, further promoting desert socioeconomic development. [ABSTRACT FROM AUTHOR]

Biological soil crusts (hereafter, “biocrusts”) dominate soil surfaces in nearly all dryland environments. To better understand the influence of water content on carbon (C) exchange, we assessed the ability of dual-probe heat-pulse (DPHP) sensors, installed vertically and angled, to measure changes in near-surface water content. Four DPHP sensors were installed in each of two research plots (eight sensors total) that differed by temperature treatment (control and heated). Responses were compared to horizontally installed water content measurements made with three frequency-domain reflectometry (FDR) sensors in each plot at 5-cm depth. The study was conducted near Moab, Utah, from April through September 2009. Results showed significant differences between sensor technologies: peak water content differences from the DPHP sensors were approximately three times higher than those from the FDR sensors; some of the differences can be explained by the targeted monitoring of biocrust material in the shorter DPHP sensor and by potential signal loss from horizontally installed FDR sensors, or by an oversampling of deeper soil. C-exchange estimates using the DPHP sensors showed a net C loss of 69 and 76 g C m −2 in control and heated plots, respectively. The study illustrates the potential for using the more sensitive data from shallow installations for estimating C exchange in biocrusts. [ABSTRACT FROM AUTHOR]

The impacts of oil pollution, unlike other disturbances, on the structure and activity of microorganisms in biological soil crusts have never been investigated. We exposed crust pieces from Wadi Al-Khoud, Sultanate of Oman to different oil concentrations and studied changes in their chlorophyll a (Chl a ) content, bacterial communities and photosynthetic and respiration activities. Chl a concentrations did not change in dry oil-polluted crusts but increased in the crusts exposed to oil in the presence of water. Nevertheless, extended incubation with oil for ≥3 weeks or in the presence of higher concentrations resulted in a considerable decline in Chl a in the wet polluted crusts. A remarkable shift in the bacterial community composition of oil-polluted crusts was detected, with the replacement of Cyanobacteria by Firmicutes . Sequences affiliated to Firmicutes constituted 86% of total sequences after 96 days of incubation with oil. This community shift was concomitant with alkanes degradation, as assessed by gas chromatography-mass spectrometry (GC–MS) analysis. Using oxygen microsensors, addition of oil to crusts was shown to result in an instantaneous decline in oxygen production but a quick recovery within hours of incubation. The net oxygen production and net photosynthesis decreased whereas the recovery time increased with increasing concentrations of oil. Recovery was not possible when crusts were exposed to ≥2000 mg oil g −1 crust. Incubation of crust pieces at different oil concentrations in air-tight bottles in the dark showed an increase in CO 2 evolution with increasing oil concentration. We conclude that oil pollution has drastic effects on crust microorganisms, and these effects depend on oil pollution levels, hydration conditions and duration of exposure. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) dominate the interspace between sparse vegetation in arid and cold environments worldwide and fulfill diverse ecosystem functions. Natural BSCs are usually classified as a series of stepwise successional stages along with a gradual improvement of biological properties and micro-environmental conditions. However, the effects of spatial heterogeneity on the ecological traits of BSCs remain largely unknown, especially in the microbial scenario. In this study, three adjacent biocrust elements with different successional levels (cyanobacterial, lichen, and moss crusts) were collected from a continuous and heterogeneous crustal community at small scale (centimetre level) in the Gurbantünggüt Desert, aiming to distinguish the alteration of microbial distribution and functional traits among them. The catabolic fingerprint of sole-carbon induced respiration was measured by MicroResp™ respiration system to calculate the functional diversity indices. Ribosomal copy numbers of different soil microbes (bacteria, fungi, and phototrophs), as a proxy for microbial relative abundance, were analysed through quantitative PCR methods. We also evaluated the related physicochemical parameters. The results show evidences that the microbial abundances and functional traits associated with each biocrust element are inconsistent with its successional level. Although higher microbial activities and more benign soil conditions (increased soil moisture and organic matter) were still found in well-developed moss crust, higher microbial abundances (except fungi) and enhanced functional diversity were observed in less-developed cyanobacterial crust. Spatial heterogeneity due to the jigsaw-like pattern of various biocrust elements partly affects microbial performances in BSCs. More studies focusing on quantitatively measuring spatial arrangement of biocrust elements are needed to clarify the mechanisms underlying to functional differentiation in crustal communities. [ABSTRACT FROM AUTHOR]

Reactive nitrogen species have a strong influence on atmospheric chemistry and climate, tightly coupling the Earth's nitrogen cycle with microbial activity in the biosphere. Their sources, however, are not well constrained, especially in dryland regions accounting for a major fraction of the global land surface. Here, we show that biological soil crusts (biocrusts) are emitters of nitric oxide (NO) and nitrous acid (HONO). Largest fluxes are obtained by dark cyanobacteria-dominated biocrusts, being ~20 times higher than those of neighboring uncrusted soils. Based on laboratory, field, and satellite measurement data, we obtain a best estimate of ~1.7 Tg per year for the global emission of reactive nitrogen from biocrusts (1.1 Tg a-1 of NO-N and 0.6 Tg a-1 of HONO-N), corresponding to ~20% of global nitrogen oxide emissions from soils under natural vegetation. On continental scales, emissions are highest in Africa and South America and lowest in Europe. Our results suggest that dryland emissions of reactive nitrogen are largely driven by biocrusts rather than the underlying soil. They help to explain enigmatic discrepancies between measurement and modeling approaches of global reactive nitrogen emissions. As the emissions of biocrusts strongly depend on precipitation events, climate change affecting the distribution and frequency of precipitation may have a strong impact on terrestrial emissions of reactive nitrogen and related climate feedback effects. Because biocrusts also account for a large fraction of global terrestrial biological nitrogen fixation, their impacts should be further quantified and included in regional and global models of air chemistry, biogeochemistry, and climate. [ABSTRACT FROM AUTHOR]

Many arid and semiarid ecosystems have soils covered with well-developed biological soil crust communities (biocrusts) made up of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface. These communities are a fundamental component of dryland ecosystems, and are critical to dryland carbon (C) cycling. To examine the effects of warming temperatures on soil C balance in a dryland ecosystem, we used infrared heaters to warm biocrust-dominated soils to 2 °C above control conditions at a field site on the Colorado Plateau, USA. We monitored net soil exchange (NSE) of CO every hour for 21 months using automated flux chambers (5 control and 5 warmed chambers), which included the CO fluxes of the biocrusts and the soil beneath them. We observed measurable photosynthesis in biocrust soils on 12 % of measurement days, which correlated well with precipitation events and soil wet-up. These days included several snow events, providing what we believe to be the first evidence of substantial photosynthesis underneath snow by biocrust organisms in drylands. Overall, biocrust soils in both control and warmed plots were net CO sources to the atmosphere, with control plots losing 62 ± 8 g C m (mean ± SE) over the first year of measurement and warmed plots losing 74 ± 9 g C m. Between control and warmed plots, the difference in soil C loss was uncertain over the course of the entire year due to large and variable rates in spring, but on days during which soils were wet and crusts were actively photosynthesizing, biocrusts that were warmed by 2 °C had a substantially more negative C balance (i.e., biocrust soils took up less C and/or lost more C in warmed plots). Taken together, our data suggest a substantial risk of increased C loss from biocrust soils with higher future temperatures, and highlight a robust capacity to predict CO exchange in biocrust soils using easily measured environmental parameters. [ABSTRACT FROM AUTHOR]

In almost all dryland systems, biological soil crusts (biocrusts) coexist alongside herbaceous and woody vegetation, creating landscape mosaics of vegetated and biocrusted patches. Results from past studies on the interaction between biocrusts and vascular plants have been contradictory. In the Gurbantunggut desert, a large temperate desert in northwestern China, well-developed lichen-dominated crusts dominate the areas at the base and between the sand dunes. We examined the influence of these lichen-dominated biocrusts on the germination, growth, biomass accumulation, and elemental content of five common plants in this desert: two shrubs ( Haloxylon persicum, Ephedra distachya) and three herbaceous plants ( Ceratocarpus arenarius, Malcolmia africana and Lappula semiglabra) under greenhouse conditions. The influence of biocrusts on seed germination was species-specific. Biocrusts did not affect percent germination in plants with smooth seeds, but inhibited germination of seeds with appendages that reduced or eliminated contact with the soil surface or prevented seeds from slipping into soil cracks. Once seeds had germinated, biocrusts had different influences on growth of shrub and herbaceous plants. The presence of biocrusts increased concentrations of nitrogen but did not affect phosphorus or potassium in tissue of all tested species, while the uptake of the other tested nutrients was species-specific. Our study showed that biocrusts can serve as a biological filter during seed germination and also can influence growth and elemental uptake. Therefore, they may be an important trigger for determining desert plant diversity and community composition in deserts. [ABSTRACT FROM AUTHOR]

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]

Many studies have shown that changes in nitrogen (N) availability affect the diversity and composition of soil microbial community in a variety of terrestrial systems, but less is known about the responses of microbes specific to biological soil crusts (BSCs) to increasing N additions. After seven years of field experiment, the bacterial diversity in lichen-dominated crusts decreased linearly with increasing inorganic N additions (ambient N deposition; low N addition, 3.5 g N m−2 y−1; medium N addition, 7.0 g N m−2 y−1; high N addition, 14.0 g N m−2 y−1), whereas the fungal diversity exhibited a distinctive pattern, with the low N-added crust containing a higher diversity than the other crusts. Pyrosequencing data revealed that the bacterial community shifted to more Cyanobacteria with modest N additions (low N and medium N) and to more Actinobacteria and Proteobacteria and much less Cyanobacteria with excess N addition (high N). Our results suggest that soil pH, together with soil organic carbon (C), structures the bacterial communities with N additions. Among the fungal communities, the relative abundance of Ascomycota increased with modest N but decreased with excess N. However, increasing N additions favored Basidiomycota, which may be ascribed to increases in substrate availability with low lignin and high cellulose contents under elevated N conditions. Bacteria/fungi ratios were higher in the N-added samples than in the control, suggesting that the bacterial biomass tends to dominate over that of fungi in lichen-dominated crusts after N additions, which is especially evident in the excess N condition. Because bacteria and fungi are important components and important decomposers in BSCs, the alterations of the bacterial and fungal communities may have implications in the formation and persistence of BSCs and the cycling and storage of C in desert ecosystems. [ABSTRACT FROM AUTHOR]

Biological Soil Crusts (BSCs) represent an important part of the living cover in drylands worldwide. BCSs change soil hydrology due to extracellular polymeric substances (EPS)-excreting species of cyanobacteria, dominant members of dryland-BSCs. The presence of EPS allowed matric potential (Ψ m ) to remain unchanged down to 20% water content, whereas, without EPS, Ψ m started decreasing at 80% water content. The EPS matrix improved the water retaining capacity of soil, suggesting that BSCs would delay onset of restrictive matric potential values due to its larger water holding capacity. [ABSTRACT FROM AUTHOR]

• High amounts of non-rainfall water (10%–15% of water input) occur in the alpine sandy land. • Biological soil crusts increase the daily mean non-rainfall water amount by 23%–30%. • Biological soil crusts enhance non-rainfall water accumulation and dissipation rates by >20%. • The effects of soil crusts can be attributed to changes in soil physicochemical properties. • The principal source of non-rainfall water is atmospheric vapor (∼60%). Non-rainfall water originating from atmospheric and soil vapors is a major water source that supports dryland ecosystem functioning. The alpine sandy land ecosystem is fragile, where biological soil crusts develop widely on the soil surface and play a critical role in regulating surface hydrological processes. Yet, the effects of biological soil crusts on non-rainfall water in the alpine sandy land remain unclear. Therefore, we investigated the patterns and main sources of non-rainfall water under different biological soil crusts in the Qinghai–Tibet Plateau region during the growing season (May–September 2017). Micro-lysimeters were used to measure the amount of non-rainfall water in surface soil (0–10 cm) covered with moss and algae crusts in an interdune area. The results revealed that non-rainfall water occurred for at least 12 h·d−1 (7 p.m.–7 a.m.) and disappeared for 5 h (7 a.m.–12 a.m.). The daily mean non-rainfall water amount ranged between 0.324 and 0.426 mm. Differences in the physical and chemical properties of surface soil caused by biological soil crusts affected the accumulation and dissipation of non-rainfall water. The accumulation and dissipation rates of non-rainfall water under biological soil crusts were respectively 1.22–1.32-fold (F = 8.01, P < 0.05) and 1.21–1.27-fold (F = 8.86, P < 0.05) higher than those of bare sand. Biological soil crusts also increased the amount of total non-rainfall water by 23.41%–30.39% (F = 5.367, P < 0.05), accounting for 2.4%–3.0% of the total water input. Atmospheric vapor condensation was the principal source of non-rainfall water (>60%). Nevertheless, biological soil crusts increased both atmospheric and soil vapor condensation by 29.44%–39.98% (F = 12.45, P < 0.05) and 13.09–13.94% (F = 5.91, P < 0.05), respectively. Although non-rainfall water contributed only 10%–15% of the total water input, it constituted a main water input to the ecosystem during the dry period of less rainfall (up to 20%, 19.72 vs. 95.72 mm). In conclusion, non-rainfall water, especially atmospheric vapor condensation, makes a non-negligible contribution to water input in the alpine sandy land ecosystem, for which biological soil crusts enhance the role of non-rainfall water in the water input in surface soil water balance dynamics. [ABSTRACT FROM AUTHOR]

Cyanobacteria occur worldwide but play an important role in the formation and primary activity of biological soil crusts (BSCs) in arid and semi-arid ecosystems. The cyanobacterial diversity in BSCs of the northwest Negev desert of Israel was surveyed at three fixed sampling stations situated along a precipitation gradient in the years 2010 to 2012. The three stations also are characterized by marked differences in soil features such as soil carbon, nitrogen, or electrical conductivity. The cyanobacterial biodiversity was analyzed by sequencing inserts of clone libraries harboring partial 16S rRNA gene sequences obtained with cyanobacteria-specific primers. Filamentous, non-diazotrophic strains (subsection III), particularly Microcoleus-like, dominated the cyanobacterial community (30 % proportion) in all years. Specific cyanobacterial groups showed increased (e.g., Chroococcidiopsis, Leptolyngbya, and Nostoc strains) or decreased (e.g., unicellular strains belonging to the subsection I and Scytonema strains) abundances with declining water availability at the most arid, southern station, whereas many cyanobacterial strains were frequently found in the soils of all three stations. The cyanobacterial diversity at the three sampling stations appears dependent on the available precipitation, whereas the differences in soil chemistry were of lower importance. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) are highly complex associations of soil particles with mosses, cyanobacteria, lichens, bacteria, and fungi. BSCs affect many ecological processes, including infiltration and evaporation, soil erosion, vegetation succession, and nutrient cycling, and perform important ecological functions of ecosystems in arid areas. In the past 30 years, many studies on BSCs were conducted by researchers all over the world. This paper reviews the recent research progresses and frontier problems, and discusses the current controversial conclusions. The main ideas are as follows: (1) influenced by many macroclimate and micro-environment factors, BSCs are characterized by developmental complexity, composition diversity, and spatial heterogeneity. In any typical areas where exist all types of BSCs at different succession stages, it is of great significance to conduct comparable studies on BSCs and to explore if there exists a probable zonality for them. (2) BSCs not only exert positive impacts on soil fertility and soil erosion, but they also show controversial influences on the hydrological processes, especially on infiltration, evaporation, soil moisture, and vegetation succession such as survival, germination, emergence, and establishment. To understand the function-performing mechanisms of BSCs is helpful for the revealing of their action patterns and the comprehension of the implications of the patterns on ecological processes and restoration as well as clarification of existing controversial points. It will eventually contribute to the effective management and utilization of BSCs resources in a given region for large-scale ecological engineering. [ABSTRACT FROM AUTHOR]

A significant proportion of the Earth's surface is desert or in the process of desertification. The extreme environmental conditions that characterize these areas result in a surface that is essentially barren, with a limited range of higher plants and animals. Microbial communities are probably the dominant drivers of these systems, mediating key ecosystem processes. In this review, we examine the microbial communities of hot desert terrestrial biotopes (including soils, cryptic and refuge niches and plant-root-associated microbes) and the processes that govern their assembly. We also assess the possible effects of global climate change on hot desert microbial communities and the resulting feedback mechanisms. We conclude by discussing current gaps in our understanding of the microbiology of hot deserts and suggest fruitful avenues for future research. [ABSTRACT FROM AUTHOR]

The nitrogen cycle is highly sensitive to pollutants and restoration of this biogeochemical pathway is essential to ensure long-term sustainable ecosystems. Due to their ability to fix nitrogen, some native herb species and Biological Soil Crusts (BSCs) may promote plant community growth and help to establish primary successional processes. In a greenhouse trial, growth and nitrogen fixation rates of yellow mountain aven (Dryas drummondii), alpine sweetvetch (Hedysarum alpinum), field locoweed (Oxytropis campestris) and arctic lupine (Lupinus arcticus) were determined in tailings and mining impacted soils with amendments of Rhizobia and biochar. In a growth chamber trial, Pure Nostoc commune culture, Dried Nostoc spp. and BSC slurries derived from mature soil crusts were applied with and without biochar to tailings. Arctic lupine had the highest biomass and all species except yellow mountain aven showed nitrogen fixation in tailings and mining impacted soils. Nodulation and nitrogen fixation only occurred in herbs given a Rhizobia inoculum, suggesting the use of nitrogen-fixing species in northern reclamation may require microbial amendments. When used in combination with Rhizobia inoculum, biochar may promote nitrogen fixation associated with herb species. BSC slurries from mature soil crusts had significantly higher mean rates of nitrogen fixation (95 µmol N m²/hr) compared with other soil crust species (5-23 µmol N m²/hr). Biochar, Rhizobial inoculants and native nitrogen fixing species can enhance revegetation and nitrogen input in northern mining impacted substrates. However, large scale field experiments are required to identify suitable landscapes and determine how these initial nitrogen fixing species influence subsequent succession. [ABSTRACT FROM AUTHOR]

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]

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]

The nitrogen cycle affects ecosystem stability. The occurrence of biological soil crusts (BSCs) in a desertified region significantly affects the nitrogen cycle. BSCs are gradually forming on the sand surface of a sand-fixing plantation in semi-arid Horqin Sandy Land, Northeast China. However, the composition of microbial nitrogen-cycling communities remains unknown. This study aimed to investigate the diversities of nitrogen-fixing, ammonia-oxidizing, and denitrifying bacteria in BSCs of a sand-fixing plantation. Soil samples were obtained from three plantations, namely, Caragana microphylla Lam., Hedysarum fruticosum , and Artemisia halodendron . The bacterial community was characterized by 16S rDNA sequence analysis. Denaturing gradient gel electrophoresis (DGGE), cloning, and sequencing were used to determine the diversities of nifH , ammonia-oxidizing 16S rRNA, and nosZ genes. Results of 16S rDNA gene phylogenetic analysis indicate that the phyla Proteobacteria, Acidobacteria, Bacteroidetes, and Actinobacteria were dominant groups. Samples from the three plantations displayed similar DGGE profiles for the three genes, suggesting that plantation type had no influence on the dominant population of nitrogen-cycling bacterial communities. Most sequences of nifH formed a distinct cluster that branched with known Azotobacter diazotrophs. Sequence analysis of the bacterial 16S rRNA gene showed that the ammonia-oxidizing community comprised uncultured Nitrosomonas species and Nitrosospira members affiliated with Nitrosospira cluster 3. Although nosZ genes belong to three subclasses of Proteobacteria, almost half are closely affiliated with Pseudomonas of Gammaproteobacteria. This study demonstrated that the dominant phylum in BSCs was Proteobacteria. [ABSTRACT FROM AUTHOR]

How soil cover types and rainfall patterns influence carbon (C) release in temperate desert ecosystems has largely been unexplored. We removed intact crusts down to 10 cm from the Shapotou region, China, and measured them in PVC mesocosms, immediately after rainfall. C release rates were measured in soils with four cover types (moss-crusted soil, algae-crusted soil, mixed (composed of moss, algae, and lichen)-crusted soil, and mobile dune sand). We investigated seven different rainfall magnitudes (0-1, 1-2, 2-5, 5-10, 10-15, 15-20, and >20 mm) under natural conditions. C release from all four BSCs increased with increasing rainfall amount. With a rainfall increase from 0 to 45 mm, carbon release amounts increased from 0.13 ± 0.09 to 15.2 ± 1.35 gC m in moss-crusted soil, 0.08 ± 0.06 to 6.43 ± 1.23 gC m in algae-crusted soil, 0.11 ± 0.08 to 8.01 ± 0.51 gC m in mixed-crusted soil, and 0.06 ± 0.04 to 8.47 ± 0.51 gC m in mobile dune sand, respectively. Immediately following heavy rainfall events (44.9 mm), moss-crusted soils showed significantly higher carbon release rates than algae- and mixed-crusted soils and mobile dune sands, which were 0.95 ± 0.02, 0.30 ± 0.03, 0.13 ± 0.04, and 0.51 ± 0.02 μmol CO m s, respectively. Changes in rainfall patterns, especially large rain pulses (>10 mm) affect the contributions of different soil cover types to carbon release amounts; moss-crusted soils sustain higher respiration rates than other biological crusts after short-term extreme rainfall events. [ABSTRACT FROM AUTHOR]

In arid and semiarid areas of the planet, biological soil crusts (BSCs) participate in functions critical to the ecosystem sustainability and are usually located in inter-vegetation spaces. These crusts are structurally and in terms of biomass dominated by mosses and lichens. Associated with them, a great variety of fungi, bacteria, and cyanobacteria have been found. Despite their ecological importance, major details of the functionalities of the microbial communities inhabiting BSCs and the underlying soil are still missing. Here, we explore the biomass, functionality, and protein-based phylogeny of the microbial communities associated with lichen-dominated BSCs under a semiarid climate. Two lichen-dominated BSCs (Fulgensia desertorum -dominated BSC, F-BSC; and Squamarina cartilaginea -dominated BSC, S-BSC) were sampled in a semiarid soil located in South-East Spain. Samples of the BSCs and the underlying soils were collected. The biomass and activity of the microbial community in both BSCs was higher than in the soil underlying them, as estimated by their PLFA content, basal respiration, and enzyme activities. The factor analysis of PLFAs and the putative phylogenetic analysis of the identified proteins indicated scarce differences in the composition of the microbial communities of the two biocrusts at the phylum level. In contrast, community-level physiological profiles (CLPPs) revealed that the microbial communities inhabiting BSCs metabolized substrates differently. The identification of ribulose-1,5 biphosphate carboxylase oxygenase (RuBisCO) peptides points to a specialization in carbon fixation which is carried out by some cyanobacterial species in F-BSC, such as Prochlorothrix hollandica and Microcoleus vaginatus, but not in S-BSC. The structure of the microbial community in the soil underlying each BSC was different, as estimated by factor analysis of PLFAs, but such differences did not correspond to changes in the functional structure, as indicated by the CLPPs. The multidisciplinary approach used in this study revealed remarkable differences between the microbial communities inhabiting F. desertorum and S. cartilaginea -dominated biological crusts, whereas the microbial communities in the soils underlying the two crusts behaved similarly. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biological soil crusts significantly increased soil enzyme activities. [•] Moss crusts had greater soil enzyme activities than cyanobacteria–lichen crusts. [•] The elapsed time since sand dune stabilization correlated positively with soil enzyme activity. [•] Soil enzyme activities under crusts varied with soil depth and season. [Copyright &y& Elsevier]

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]

This study provides estimates of N2 fixation in biological soil crusts (BSCs) from shrub-steppe grasslands in British Columbia's Chilcotin plateau. We identify key seasonal periods and environmental conditions during episodes of BSC nitrogen-fixation activity. Predicted nitrogen-fixation activity showed two peak periods: one during late winter and early spring snowmelt events, and the second during summer precipitation events. BSC nitrogen fixation, especially summer activity, was quite variable from year to year. The magnitude of predicted nitrogen fixation at the landscape level was dependent upon the ratio used to convert rates of acetylene reduction to nitrogen fixed. Using a theoretical ratio of 3:1, estimates of average annual BSC nitrogen fixation were 1.0 kg N·ha−1. However, using a conversion ratio of 0.06, obtained from side-by-side measurements of acetylene reduction and 15N uptake, annual estimates are 52 kg N·ha−1. These estimates are based on assessments of the aerial extent of dark BSC communities, which at the Farwell Canyon study site exceeded 50%. The fate of fixed nitrogen, especially during the late winter period, when underlying soils are frozen, remains unclear. [ABSTRACT FROM AUTHOR]

Abstract: Morphological and physiological characteristics of biological soil crusts (BSCs) enhance soil stability and fertility, and influence soil chemistry. However, the effect of BSCs on soil physico-chemical properties may vary depending on taxa (cyanobacteria, lichen, bryophytes) and species, and be susceptible to soil surface disturbance. We examined a wide variety of soil physico-chemical properties associated with five BSC components (cyanobacteria crust, one moss species, three lichen species) naturally occurring in the study area, and bare soil along a disturbance gradient in a semiarid grassland ecosystem in Central Mexico. We addressed the following questions: 1) Do different BSC components create distinct soil microsites characterized by a particular combination of physico-chemical properties? 2) Do distinct soil properties change beneath different BSC components? 3) Does grazing disturbance modify or override species-specific BSC effects? We found that BSC components and bare soil generated distinct soil microsites, however, this effect diminished with increasing grazing pressure. Also, most of the soil variables examined differed between BSC components and bare soil along the gradient. While soil properties associated with cyanobacteria were relatively similar compared to bare soil along the gradient, Diploschistes diacapsis and Lecidella sp. showed decreases in pH and marked differences in mineral nutrient concentration (i.e. variations in Na, Fe and Zn concentration respect to other BSC components and bare soil). Grazing intensity and frequency changed species-specific effects of D. diacapsis, specially modifying its effect on soil texture, diminishing its effect on pH, K and Na concentration, and increasing its effect on Ca and Zn concentration. We conclude that BSC components contribute to natural small-scale soil heterogeneity, and that soil disturbance substantially modifies the nature and magnitude of this effect with potentially important implications on ecosystem processes. Because of the potential influence of other factors (i.e. climate, vascular plants, microbial activity) on BSCs' relation to soil properties, this assertion should be tested including these factors and in multiple ecosystems. [Copyright &y& Elsevier]

Ecosystem invasibility is determined by combinations of environmental variables, invader attributes, disturbance regimes, competitive abilities of resident species and evolutionary history between residents and disturbance regimes. Understanding the relative importance of each factor is critical to limiting future invasions and restoring ecosystems., We investigated factors potentially controlling Bromus tectorum invasions into Artemisia tridentata ssp. wyomingensis communities across 75 sites in the Great Basin. We measured soil texture, cattle grazing intensity, gaps among perennial plants and plant cover including B. tectorum, biological soil crusts ( BSCs) and bare soil. Using a priori knowledge, we developed a multivariate hypothesis of the susceptibility of Artemisia ecosystems to B. tectorum invasion and used the model to assess the relative importance of the factors driving the magnitude of such invasions., Model results imply that bunchgrass community structure, abundance and composition, along with BSC cover, play important roles in controlling B. tectorum dominance. Evidence suggests abundant bunchgrasses limit invasions by limiting the size and connectivity of gaps between vegetation, and BSCs appear to limit invasions within gaps. Results also suggest that cattle grazing reduces invasion resistance by decreasing bunchgrass abundance, shifting bunchgrass composition, and thereby increasing connectivity of gaps between perennial plants while trampling further reduces resistance by reducing BSC., Synthesis and applications. Grazing exacerbates Bromus tectorum dominance in one of North America's most endangered ecosystems by adversely impacting key mechanisms mediating resistance to invasion. If the goal is to conserve and restore resistance of these systems, managers should consider maintaining or restoring: (i) high bunchgrass cover and structure characterized by spatially dispersed bunchgrasses and small gaps between them; (ii) a diverse assemblage of bunchgrass species to maximize competitive interactions with B. tectorum in time and space; and (iii) biological soil crusts to limit B. tectorum establishment. Passive restoration by reducing cumulative cattle grazing may be one of the most effective means of achieving these three goals. [ABSTRACT FROM AUTHOR]

Aims: As an important successional stage of biological soil crusts, lichen soil crusts (LSCs) are often in the dry and inactive state in desert environments, so it is vital for their survival and development in these areas to reactivate the photosynthetic systems during a rehydration event. Methods: In this study, the reactivation patterns of light-harvesting complexes (LHCs) and reaction centres of photosystem (PS) II in the long-term desiccated LSCs (approximately 10 months) were monitored using chlorophyll a fluorescence technique. Results: For the long-term desiccated LSCs, PS II reaction centres could recover their activity gradually in the light after rehydration, whereas no obvious recovery occurred in the dark (0.1< Fv/Fm<0.2). After experiencing prior rehydration/desiccation (R/D) cycle(s) in the light, the PS II reaction centres could rapidly recover their activity following rehydration both in the light and dark. Even the most reactivation (76 % of the PSII centers) was independent on the synthesis of new proteins. In addition, compared with reaction centres, LHCs of PS II could recover their activity faster both in the light and dark, and prior R/D cycle(s) also accelerated the recovery of LHC II. Conclusions: It is concluded that prior R/D cycles strongly accelerated LSC recovery process of photosynthetic systems and removed the dependence on light in subsequent hydration events. This characteristic is essential for LSCs to survive and develop in desert environments because it facilitates more carbon fixation during transient rehydration. [ABSTRACT FROM AUTHOR]

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: Carbon flux represents carbon uptake from or release to the atmosphere in desert ecosystems, yet the changing pattern of carbon flux in desert ecosystems and its dependence on soil cover type and rainfall amount are poorly understood. We measured net carbon fluxes (NCF) in soil with four cover types (moss crusted soil, cyanobacteria/lichen crusted soil, bareland and semishrub Ephedra distachya-inhabited site) from April to October of 2010 and 2011, and NCF and dark respiration (DR) after four rainfall amounts (0, 2, 5, and 15 mm) in cyanobacteria/lichen crusted soil, bareland and the E. distachya-inhabited site. NCF in the E. distachya-inhabited site differed significantly from those of the other three soil cover types, while no difference was observed between the moss and cyanobacteria/lichen crusted soils or between the two crusted soils and bareland on most measurement occasions. NCF ranged from −0.28 ± 0.14 to 1.2 ± 0.07 μmol m−2 s−1 in the biologically crusted soils, and from −2.2 ± 0.27 to 0.46 ± 0.03 μmol m−2 s−1 at the E. distachya-inhabited site. Daily NCF in the biologically crusted soils and bareland showed carbon release at most times and total carbon production ranged from 48.8 ± 5.4 gC m−2 yr−1 to 50.9 ± 3.8 gC m−2 yr−1, while the E. distachya-inhabited site showed a total carbon uptake of −57.0 ± 9.9 gC m−2 yr−1. Daily variances in NCF were well-explained by variances in surface soil temperature, and seasonal NCF showed a significant linear relationship with soil moisture in the two biologically crusted soils and bareland when soil volumetric water content was less than 3%. Rainfall elicited intense carbon release in cyanobacteria/lichen crusted soil, bareland and at the E. distachya-inhabited site, and both NCF and DR were positive in the first two days after rainfall treatments. Mean NCF and DR were not different between rainfall amounts of 2, 5 and 15 mm in cyanobacteria/lichen crusted soil and bareland, while they were significantly higher after 15 mm rainfall treatment compared with 2 mm and 5 mm treatments at the E. distachya-inhabited site. Mean NCF and DR in the first two days increased logistically with rainfall amount. Based on our findings, we suggest that E. distachya-inhabited sites contribute to carbon uptake in the Gurbantunggute Desert, while biologically crusted soils exhibit carbon release for most of the year. Even though photosynthesis immediately following rainfall can be stimulated, carbon uptake effect in biologically crusted soil is likely intermittent and confined to periods when moisture is available. [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]

Abstract: Biological soil crusts (BSCs) are important sources of carbon input to ecosystems in arid and semiarid regions, where vascular plants are restricted by the rigorous environment and limited soil water. Sand dune stabilization by revegetation can enhance colonization and development of BSCs on sandy soil surfaces, and convert BSCs from the early successional stage dominated by cyanobacteria and algae to the later stage dominated by lichens and mosses. This study estimated the carbon fixation by two successional stages of BSCs based on four years of field observations. Carbon fixation by two BSCs has been compared via estimating daily carbon fixation using measuring net photosynthesis with ten sampling plots per crust stage in situ, combining with calculating the wet daytime of crustal cryptogam thallus. However, diurnal carbon fixation of both BSCs was largely determined by crustal water content rather than photosynthesis photon flux and temperature. The range of optimal gravimetric water content for early BSCs was 1–3.5%, and 1–5% for the later BSCs. The annual carbon fixation was 11.36gCm−2 yr−1 for cyanobacteria–algae dominated crusts and 26.75gCm−2 yr−1 for lichen–moss dominated crusts. The latter had a higher carbon input due to a higher water-holding capacity, prolonging wet daytime and higher chlorophyll content, as well as higher light capture. These findings indicate the recovery of BSCs is expected to significantly increase carbon input into sandy desert ecosystems. [Copyright &y& Elsevier]

Molecular methodologies were used to investigate fungal assemblages of biological soil crusts (BSCs) from arid lands in the southwestern United States. Fungal diversity of BSCs was assessed in a broad survey that included the Chihuahuan and Sonoran deserts as well as the Colorado Plateau. At selected sites samples were collected along kilometer-scale transects, and fungal community diversity and composition were assessed based on community rRNA gene fingerprinting using PCR-denaturing gradient gel electrophoresis (DGGE). Individual phylotypes were characterized through band sequencing. The results indicate that a considerable diversity of fungi is present within crusted soils, with higher diversity being recovered from more successionally mature BSCs. The overwhelming majority of crust fungi belong to the Ascomycota, with the Pleosporales being widespread and frequently dominant. Beta diversity patterns of phylotypes putatively representing dominant members of BSC fimgal communities suggest that these assemblages are specific to their respective geographic regions of origin. [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]

Abstract: Biological soil crusts (BSCs) are highly specialized topsoil microbial communities commonly found in arid and semiarid environments, permeated by a polymeric matrix of polysaccharides. BSCs can in principle influence edaphic properties such as texture, pore formation and water retention, which in turn determine water distribution and biological activity in dry lands. This paper investigates the influence of biotic and abiotic factors on BSC hydraulic conductivity, a parameter gauging the ease with which water can move through the pore spaces. Texture, phototroph abundance, microbial composition, and extracellular carbohydrate content were considered as potentially relevant parameters in a correlational study of BSC samples that spanned 1.5 orders of magnitude in hydraulic conductivity. A newly developed, non-destructive extraction method enabled us to directly quantify the specific role of extracellular polysaccharides on soil permeability on a variety of samples. Hydraulic conductivity showed a strongest correlation with texture (positive with sand content, negative with silt and clay). A weaker negative correlation with carbohydrate content, especially with polysaccharides having a molecular weight < 100 kDa, was also detected. In multiple regression analyses texture (silt content) was sufficient to explain most of the variation in hydraulic conductivity However, experimental removal of polymeric carbohydrates, resulted invariably in a substantial decrease in hydraulic conductivity for any given sample (between 1.7 and 3.3 fold). Our results suggest that while soil texture determines overall hydraulic conductivity in BSCs, the presence of exopolysaccharides can significantly enhance it, likely by conferring a spongy structure to a BSC thus increasing the number of waterways within it. [Copyright &y& Elsevier]

Aims: In Dalateqi region of Inner Mongolia (at eastern edge of Qubqi Desert), man-made algae crusts were constructed with two filamentous cyanobacteria. Two to three years later, the algae crusts began to succeed to moss crusts under some microterrain conditions. In order to characterize the community structure and compare the photosynthetic characteristics in different successional stages of biological soil crusts (BSCs). Methods: This paper studied composition of photosynthetic organisms and diurnal changes of photosynthetic efficiency, with microscopic observation and chlorophyll fluorescence monitoring techniques. Results: Compared with the early successional algae crusts, later moss crusts had a higher photosynthetic efficiency, which was closely related with the different community structure of photosynthetic organisms. Further, moss crusts had a higher total photosynthetic biomass, although the algal biomass decreased along the successional sequence. Similar to higher vascular plants, a midday depression of photosynthetic efficiency was detected in BSCs, although the depression extents were different in different successional stages. Analysis demonstrated the depression was mainly caused by non-stomata limitations, and photosynthetically active radiation (PAR) was a significant influencing factor in the down-regulation of photosynthetic efficiency. Conclusions: We conclude, cyanobacterial inoculation effectively promotes the formation, development and seccession of BSCs. Furthermore, the later successional BSCs have a better photosynthetic performance and thus are expected to play a more effective role in desertification control. [ABSTRACT FROM AUTHOR]

To better understand the key role of biological soil crusts (BSCs) in redistribution processes of limited water resources in semi-arid sandy ecosystems, surface runoff over BSCs in a sandy area in the southern Mu Us sandy area was observed in this study. The results indicated that runoff occurred twice among six rainfall events during the experimental period. Runoff yields varied among types of BSCs, and that they increased in the following order: light algae crusts, dark algae crusts and moss crusts. These findings showed that runoff yields were increasing with the development of BSCs. The percentage of runoff in individual rainfall events increased from light algae crusts to moss crusts, which indicated that the redistribution ratios of different types of BSCs differed. Surface runoff of BSCs may be influenced by rainfall, rain intensity, degree of water saturation of the BSCs before the rain and degree of development of BSCs. Formation of BSCs on the surface of sand dunes changed the spatial distribution pattern of water in this semi-arid sandy ecosystem, which increased the heterogeneity of resources such as water and nutrients. Therefore, making appropriate disturbances of BSCs during storm season is beneficial to maintaining the balance of natural resources in the semi-arid sandy ecosystem. [ABSTRACT FROM AUTHOR]

Biological soil crusts occur in dry land worldwide. However, studies on the carbon exchange of crusts with different histories of crust development are rare, especially in terms of the responses of carbon exchange to increasing atmospheric CO2 concentrations and decreasing water contents of crust organisms. In this study, we classified sites in Shapotou in the Tengger Desert as recent (site revegetated in 1981 in mobile sand dunes) and old (site revegetated in 1956) successional stages, and systematically analyzed the changes in the carbon exchange of cyanobacterial-algal crusts developed in the two sites to dehydration, air temperature (15 and 25 °C), and CO2 concentration (200–2000 ppm). The old crusts had a higher carbon exchange rate than the recent crusts during dehydration, and the maximum carbon exchange rates were 3.49 and 2.45 µmol · m−2 · s−1 for the old and recent crusts, respectively, at an approximately 60% water content of dry crust organisms. The carbon exchange rate was higher at 25°C than at 15°C for both crusts. No difference in the CO2 saturation points between the two crusts and between the two temperatures was observed, however, the saturation point significantly increased with the increase in the water content of the crust organisms, from 224 to 1384 ppm, when the water content of the crust organisms was increased from 20% to 100%. The water content of the crust organisms was the regulating factor for the carbon exchange rate of both the old and recent cyanobacterial-algal crusts. [ABSTRACT FROM AUTHOR]

Quantification of the relationship between surface albedo and surface temperature was done by analyzing measured diurnal variations of surface albedo and surface temperature on the biological soil crusts and sand dunes within vegetation-stabilized desert ecosystems. The surface albedos and surface temperatures of sand dunes and biological soil crusts were measured concurrently over field plots of the moving sand area and the artificially revegetated area established in 1964 in Shapotou area, on the southeastern edge of the Tengger Desert. Results indicated that the diurnal variation of surface albedo for both dry surfaces showed an upward-facing parabolic curve on clear days and was symmetrical at about local noon. Whereas, the diurnal trend of surface temperature was opposite to that of surface albedo in the daytime and asymmetrical at about local noon times. Thereby, the data were empirically divided into forenoon and afternoon data with respect to local noon to analyze the relationship between surface albedo and surface temperature. A highly correlated negative linear relationship was found in the two time periods, respectively, and we proposed an empirical model between surface albedo and surface temperature based on that relationship. The model results indicate a good potential application for using the surface temperature to specify surface albedo. [ABSTRACT FROM AUTHOR]

Abstract: Disturbance by domestic grazing is recognized as the most widespread stressor of biological soil crust (BSC) communities. To assess the recovery of the BSC after grazing exclusion, we estimated the composition, cover, and spatial distribution of biological soil crusts, and their influence on soil nitrogen in a protected area after 40 years of grazing exclusion (Reserve MaB of Ñacuñán), and in its surrounding grazed matrix in the central Monte Desert. We considered two spatial scales: at the landscape scale we estimated vegetation and BSC cover in paired grazed and ungrazed sites of Larrea shrublands; at the microsite scale we assessed the influence of the dominant vascular plant, Larrea cuneifolia, on crust cover, and the influence of crust cover on soil nitrogen concentration. Grazing has a negative impact on soil crusts, which only develop under the protection of vascular plants in grazing areas. Grazing exclusion favors crust recovery, allowing black, lichen dominated crusts to develop in exposed areas between shrub canopies. The cover of the moss-dominated crusts was not significantly different at any of the two spatial scales analyzed. Soil nitrogen was higher in areas under L. cuneifolia and without BSC cover, suggesting that litterfall inputs currently exceed those from soil crust N2 fixation, perhaps because crust function has not yet recovered. [Copyright &y& Elsevier]

Abstract: There are increasing concerns that climatic and land use changes will enhance soil respiration rates and soil organic carbon loss, compromising agricultural productivity and further elevating atmospheric CO2. Current understanding of dryland respiration is, however, insufficient to enable prediction of the consequences of these changes for dryland soils and CO2 fluxes. The objectives of this paper are to present in-situ respiration data from five remote sites along a climatic gradient in the Kalahari of Botswana and to determine the effects of temperature, moisture and biological crust cover on soil CO2 fluxes. Moisture was the primary limiting factor to efflux which increased with amount of simulated rainfall. On dry soils, mean CO2 efflux was between 1.5 and 5.9mgC m−2 h−1. After 2mm and 50mm simulated wetting, mean rates increased to 4.0 to 21.8 and 8.6 to 41.5mgCm−2 h−1 respectively. Once wet, soil CO2 efflux increases with temperature, and sites at the hotter northern end of the transect lost more CO2 than cooler southerly sites. Net respiration rates are, however, muted by autotrophic organisms in biological soil crusts which photosynthesise and take up CO2. The temperature sensitivity of soil CO2 efflux increased with moisture. Dry, 2mm and 50mm treated soils had a Q 10 of 1.1, 1.5 and 1.95 respectively. Our findings indicate that higher temperatures and a loss of biological crust cover will lead to greater soil C loss through respiration. [Copyright &y& Elsevier]

Abstract: Biological soil crusts (BSCs) play an important role in the dune fixation and maintaining soil biota in arid desert systems. Free-living soil nematode communities could be used as significant bioindicators to reflect soil recover regime after sand burial. However, the relationship between BSCs and nematodes is rarely known. To examine the effects of BSCs on soil nematodes, 72 soil samples under cyanobacteria–lichen and moss crusts were collected to analyse nematode communities in the different aged vegetated areas at the southeastern edge of the Tengger Desert. Our results showed the colonization and development of BSCs significantly enhanced nematode diversity. Nematode abundances, generic richness, H′, MI, EI and SI were greater under crusts than those under noncrust. In particular, nematode abundances, generic richness, H′, MI, EI and SI were positively correlated with crust ages. The differences in nematode communities were also dependent upon crust types. Nematode abundances and generic richness under moss crusts were higher than those under cyanobacteria–lichen crusts. This can be contributed to the present and succession of BSCs that increased thickness of topsoil after dunes have been stabilized, namely, creating suitable habitats and providing an essential food source for nematodes. [Copyright &y& Elsevier]

Biological soil crusts (BSCs) are a key biotic component of dryland ecosystems worldwide. However, most studies carried out to date on carbon (C) fluxes in these ecosystems, such as soil respiration, have neglected them. We conducted a 3.5-year field experiment to evaluate the spatio-temporal heterogeneity of soil respiration in a semiarid Stipa tenacissima steppe and to assess the contribution of BSC-dominated areas to the annual soil respiration of the whole ecosystem. We selected the six most frequent microsites in the study area: Stipa tussocks (ST), Retama sphaerocarpa shrubs (RS), and open areas with very low (<5% BSC cover, BS), low, medium and high cover of well-developed BSCs. Soil respiration rates did not differ among BSC-dominated microsites but were significantly higher and lower than those found in BS and ST microsites, respectively. A model using soil temperature and soil moisture accounted for over 85% of the temporal variation in soil respiration throughout the studied period. Using this model, we estimated a range of 240.4-322.6 g C m y released by soil respiration at our study area. Vegetated (ST and RS) and BSC-dominated microsites accounted for 37 and 42% of this amount, respectively. Our results indicate that accounting for the spatial heterogeneity in soil respiration induced by BSCs is crucial to provide accurate estimations of this flux at the ecosystem level. They also highlight that BSC-dominated areas are the main contributor to the total C released by soil respiration and, therefore, must be considered when estimating C budgets in drylands. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts are important cover in arid desert landscapes, yet their importance as habitats to secondary producers such as ants is relatively unknown. This study was conducted to determine if the presence and development of biological soil crusts on dune surfaces stabilized by revegetation facilitates ant establishment and survival. We measured topsoil properties and crustal features during different successional stages, which were characterized by cyanobacteria and algae, lichens, and mosses, respectively. The species richness and abundance (nest density) of ants were closely associated with silt content, soil organic matter, nitrogen and soil moisture, as well as topsoil temperature. However, ant nest distribution was largely dependent on the biomass and thickness of crusts and topsoil. These findings provide evidence that the recovery or development of biological soil crusts on dune surfaces in the Tengger Desert could favor and maintain higher ant species diversity. Therefore, the disturbance of crusts would result in a reduction of ant species richness and abundance in desert systems. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric nitrogen that is fixed by associative cyanobacteria can be released into the surrounding soil environment providing a key source of N for arctic ecosystems. Yet, little is known about nitrogen fixation by Biological Soil Crusts (BSCs) within hummock-hollow complexes that are typical of many arctic environments. In this study, we examined spatial and temporal patterns in N2-fixation, dinitrogenase reductase (nifH) gene abundance and release of N in a low arctic hummock-hollow ecosystem. The impacts of cyanobacteria on N status in soil were evaluated by assessing soil nitrogen in relation to the cyanobacterial associations found on Hummock and Hollow BSCs. In addition, potential P limitation of N2-fixation by cyanobacteria was assessed for Hummock and Hollow BSCs. The tops of hummocks and the bottoms of hollows were areas of high N2-fixation, whereas minimal N2-fixation occurred on the sides of hummock–hollow complexes. Compared with Hummock BSCs, Hollow BSCs had a higher mean growing season N2-fixation rate, a higher mean growing season nifH abundance, a higher mean total %N and δ15N values closer to that of atmospheric N2. Soil N status was linked to rates of N2-fixation by BSCs indicating that these N2-fixing associations act as important point sources of soil N in this low arctic ecosystem. Over the course of a growing season temporal variation in N2-fixation and nifH abundance were weakly linked suggesting that N2-fixation was carried out by complex communities of diazotrophic microorganisms and that factors such as nutrient availability may limit N2-fixation to a greater extent than nifH abundance. [ABSTRACT FROM AUTHOR]

Abstract: As a primary successional stage of biological soil crusts (BSCs), cyanobacterial crusts form firstly in the arid and semiarid areas. At the same time, they suffer many stress conditions, such as drought, salt, etc. In this study, we constructed man-made cyanobacterial crusts with Microcoleus vaginatus Gom. and comparatively studied the effects of drought and salt stresses on the crusts. The results showed that crust growth and photosynthetic activity was significantly inhibited by the stress conditions (P < 0.05), and inhibitory effect increased with the increasing stress intensity and treated time. Compared with salt stress, drought completely stopped crust metabolic activity, so the crust biomass was conserved at a higher level, which meant that drought itself might provide the crusts some protection, especially when the crusts simultaneously suffered drought and salt stresses. That is very important for the survival of crusts in the high-salt areas. In addition, to some extent the crusts could adapt to the stress conditions through metabolic adjustment. In our experiment, we found the accumulation of exopolysaccharides (EPS) increased under stress conditions within a certain threshold. [Copyright &y& Elsevier]

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]