Biological Soil Crusts Research Articles

Rainfall pulses increased short-term biocrust chlorophyll but not fungal abundance or N availability in a long-term dryland rainfall manipulation experiment

Microbial activity in drylands is mediated by the magnitude and frequency of growing season rain events that will shift as climate change progresses. Nitrogen is often co-limiting with water availability to dryland plants. This study investigated how microbes important to the nitrogen (N) cycle and soil N availability varied temporally and spatially in the context of a long-term rainfall variability experiment in the northern Chihuahuan Desert. Specifically, biological soil crust (biocrust) chlorophyll content, fungal abundance, and inorganic N were measured in soils adjacent to individuals of the grassland foundation species, Bouteloua eriopoda, and in the unvegetated interspace at multiple time points associated with experimental monsoon rainfall treatments. Treatments included 12 small weekly (5 mm) or 3 large monthly (20 mm) rain events, which had been applied during the summer monsoon for nine years prior to this study. Additionally, target plant C:N ratios were measured, and 15N-glutamate was added to biocrusts to determine potential for nutrient transport to B. eriopoda. Biocrust chlorophyll was up to 67% higher in the small weekly and large monthly rainfall treatments compared to ambient controls. Fungal biomass was 57% lower in soil interspaces than adjacent to plants but did not respond to rainfall treatments. Ammonium and nitrate concentrations near plants declined through the sampling period but varied little in soil interspaces. There was limited movement of 15N from interspace biocrusts to leaves but high 15N retention occurred in the soils even after additional ambient and experimental rain events. Plant C:N ratio was unaffected by rainfall treatments. The long-term alteration in rainfall regime in this experiment did not change how short-term microbial abundance or N availability responded to the magnitude or frequency of rain events at the end of the growing season, suggesting a limited response of N availability to future climate change.

Development of biological soil crust prompts convergent succession of prokaryotic communities

Biological soil crusts (BSCs) are vital components of desert ecosystems. Developments of BSCs enrich nutrients, create niche differentiation and drive the variations of soil microbiota. However, how BSC developments drive the dynamics of soil prokaryotic and fungal community similarities and community assemblages remain fully elusive. Here, we evaluated the variations of microbial taxonomic and phylogenetic similarities with the developmental stages of BSC. Results showed that prokaryotic communities tended to be convergent in later BSC stages, mainly driven by the environmental filtering through nutrient accumulation. Deterministic processes and stochastic processes dominated in prokaryotic and fungal community assemblages, respectively. Most prokaryotic generalists (e.g., Actinobacteria, Proteobacteria and Thaumarcaeota) and generalists of lichenized fungi were more abundant in later BSC stages. Some prokaryotic generalists (e.g., Bacteroids, Cyanobacteria, Deltaproteobacteria) showed possible symbiotic (positive) relationships with generalists of lichenized fungi. BSC development promoted the abundances of prokaryotic generalists, but reduced prokaryotic specialists and both fungal generalists and specialists through increasing primary productivity. Additionally, prokaryotic co-occurrence networks (Co-MENs) tended to be less complex and less connected. Overall, the increases of prokaryotic generalists and decreases of specialists and less complex Co-MENs supported that prokaryotic communities were more convergent in later BSC stages. Our results provided mechanistic understandings of the interactions among microbial community succession, niche specialization and BSC development.

Microsite enhancements for soil stabilization and rapid biocrust colonization in degraded drylands

In dryland ecosystems, natural recovery of biological soil crusts (biocrusts) following disturbance may be slow or inhibited, necessitating active restoration practices. While biocrusts can be readily propagated under environmentally controlled conditions, rehabilitation in the field is complicated by environmental stresses which may be particularly acute in degraded, destabilized soils with harsh climatic conditions at the soil surface. In this study, we first present the results of a field trial at a severely degraded rangeland site examining the stabilizing effects of various soil amendments (polysaccharide glues and polyacrylamides) in combination with biocrust inoculum. We found that a psyllium compound was the only amendment to maintain effectiveness after 19 months, and the only treatment that maintained biocrust inoculum throughout the trial. In a subsequent short‐term experiment where plots were shaded and watered, we examined how biocrust inoculation rate (0, 20, and 40% initial cover) and the psyllium‐based amendment affected biocrust growth. After 4 months, visible biocrust cover in inoculated plots was greater than in controls, but only chlorophyllaexhibited a dosage‐response to inoculum application rate, indicating preferential establishment of cyanobacteria. Psyllium did not affect biocrust development but did improve soil stability. Shade and watering buffered against temperature extremes (up to 15°C) and increased the duration of moist surface conditions necessary for biocrust growth by up to 30%, mimicking conditions more common in the fall and winter months. Our results suggest that inducing early successional biocrusts on a highly degraded site is possible with suitable microclimate conditions.

Nano-TiO2 enhances the adsorption of Cd(II) on biological soil crusts under mildly acidic conditions

Biological soil crusts (BSCs), which are ubiquitous in paddy fields, are known to remove pollutants from paddy fields systems. The Nano-TiO2 enhanced the removal of Cd(II) by BSC under acidic irrigation water was found, and its mechanism was investigated. After the addition of nano-TiO2, the Cd(II) removal efficiency of BSCS increased by 26.70% than that of pure BSCs, and the Nano-TiO2 induced faster removal velocity as well. Zeta potential and potentiometric titration results revealed that BSCs generated more negative charges and sites concentration after addition of Nano-TiO2 at acidic environment. The carboxyl and amino/hydroxyl groups were the main functional groups on BSC and the BSC + TiO2. The higher concentration of amino/hydroxyl groups in BSC + TiO2 (0.33 ± 0.08 mmol/g) was present than that of pristine BSCs (0.62 ± 0.02 mmol/g), and they were with similar concentration of phosphate groups and carboxyl groups. This result was attributed to the Nano-TiO2 stimulated the BSCs to produce more extracellular polysaccharides and proteins. Our findings would provide novel strategy for the removal of cadmium from acidic irrigation water.

Origin and significance of saccharides during initial pedogenesis in a temperate climate region

Saccharides are common constituents of soils, but their role and origin in the initial phases of pedogenesis remain unclear. Here we show the detailed composition of neutral sugars extracted from arenosols at different development stages, combined with additional lipids of diverse origins using gas chromatography-mass spectrometry (GC–MS). During the first stage (I) of development sucrose is the most abundant saccharide in the soil crust at up to 45,000 µg/g TOC. Sucrose is also the predominant compound in the second and third development stages, but its concentration decreased to the range of 1600 to 16,000 µg/g TOC. Stages II and III of soil development were characterized by a gradual increase in arabitol, mannitol and trehalose, compounds typical for fungi and lichen. Their abundances increased from several percent (compared to the major sucrose) to 10–32% for mannitol and 34–54% for trehalose. Moreover, in stage III there was a considerable increase in the contents of the saccharides: pinitol, myo-inositol, scyllo-inositol, arabinose, together with non-sugar compounds: dehydroabietic acid, p-hydroxybenzoic acid, gallic acid and sitosterol. All these latter compounds are higher plant markers, mainly derived from conifer detritus. The relationships between the ratios of trehalose/sucrose vs. (mannitol + arabitol)/sucrose and TOC vs. (mannitol + arabitol)/sucrose differentiated precisely the top soil layer of arenosols which are covered by different stages of biological soil crust. Our study shows that free sugars, supplemented by lipid biomarkers and total organic carbon contents, are good indicators of soil in the initial phase of pedogenesis.

Soil conservation in an abandoned agricultural rain-fed land through inoculation of cyanobacteria

Newly abandoned rain-fed lands, due to soil quality decline, are the main sources for soil erosion in semi-dry lands agricultural hill-slopes. However, adopting compatible environmentally friend measures have not been adequately implemented. Following various resultful laboratory studies, in this paper, we assessed the effect of field inoculation of cyanobacteria in an abandoned rain-fed land on controlling the natural rainfall-induced soil loss and improving the biological soil crust (BSC) quality mixture of two cyanobacteria (viz. Nostoc sp. and Oscilatoria sp.). The cyanobacteria were inoculated on 22.1 m × 1.83 m-sized plots located on the study hill-slope. The experiment was carried out for a rainfall period of 6 months under natural conditions. Measurements of 7 erosive rainfalls showed a considerable soil loss (i.e., 0.88 ± 0.10 to 9.79 ± 1.60 g m−2) from the un-inoculated plots (control), while cyanobacteria decreased the soil loss by 36 to 57% in comparison with those recorded for the control. Soil losses in the inoculated plots were 2.39 ± 0.24, 4.8 ± 0.58, 3.32 ± 0.33, 1.49 ± 0.12, 0.87 ± 0.12, 0.52 ± 0.05, and 0.56 ± 0.08 g m−2, from the first to last rainstorms, respectively. Our results, therefore, showed a poor linear relationship between soil loss (from both treatments) and rainfall properties. Cyanobacteria also improved organic carbon and nitrogen contents as two important BSC quality indicators to the tunes of 32 and 56%, respectively, in comparison to the control, during the study period. In winter, when environmental conditions were inappropriate for growing vegetation, the effect of cyanobacteria on soil loss reduction was found to be more tangible in comparison with spring. On the whole, our field soil inoculation under uncontrolled conditions, as pioneering research, facilitated to promising results for large-scale use of cyanobacteria to rapidly restore abandoned rain-fed lands.

Caracterización microtopográfica e influencia de las costras biológicas en la rugosidad del suelo en el centro-oeste de la Argentina

Introducción y objetivos: La influencia de las costras biológicas (CBS) en la rugosidad del suelo es una importante función de estas comunidades a nivel ecosistémico. Nuestros objetivos fueron caracterizar microtopográficamente los tipos de CBS y evaluar su efecto en la rugosidad del suelo en tres sistemas diferenciados por su grado de aridez.
 M&M: El microrelieve de las CBS y su influencia en la rugosidad se evaluaron en tres sistemas: semiárido, árido, e hiperárido; mediante técnicas diferentes y complementarias: método de la cadena, análisis fotográfico y técnica de las varillas metálicas. Para la primera se empleó un diseño en bloque, mientras que paras las otras dos se trabajó sobre los tipos de CBS dominantes en cada sistema.
 Resultados: La morfología de las CBS varió según el tipo de organismo dominante. Los musgos tuvieron una baja altura clasificándose como “suavemente ondulados”, las cianobacterias tuvieronpicos más abruptos, clasificándose como “pinaculadas” y los líquenes tuvieron dos frecuencias de alturas clasificándose como “rodante”. Las CBS influyeron en la rugosidad en los tres sitios evaluados. El sitio hiperárido fue el sitio en el que mayor impacto tuvieron las CBS en la rugosidad. El tipo de CBS que dominó influyó en el nivel de rugosidad hallado.
 Conclusiones: Las variaciones microtopográficas y el incremento en la rugosidad proporcionada por las CBS es clave en la dinámica del Monte debido a que pequeñas interrupciones sobre el terreno podrían incrementar la disponibilidad de agua y disminuir las pérdidas de nutrientes por erosión, dos aspectos fundamentales del funcionamiento de estos sistemas.

Organic carbon accumulation in the glacier forelands with regard to variability of environmental conditions in different ecogenesis stages of High Arctic ecosystems

Recently deglaciated surfaces of glacier forelands are subjected to a variety of biotic and abiotic factors that lead to continuous soil formation. Until now, no attempt has been taken to analyse multiple factors that might affect soil development in the Arctic forelands. The main aim of this research was to determine the factors that influence soil development in the eight forelands of Svalbard. Moreover, the effects of both habitat type (glacier foreland and mature tundra) and geographical location on environmental variables treated as potential factors influencing soil formation were tested. In 2017, at each location a series of 1 m2 plots was established; all 168 plots were investigated in terms of soil properties, spatial data, biological soil crusts (BSCs) properties, percent cover of BSCs and vascular plants. Stepwise multiple linear regression analysis using forward variable selection showed that soil development was significantly associated with six of fifteen analysed factors, i.e. BSC cover, carbon and nitrogen content in BSCs, soil pH, Topographic Wetness Index and foreland location. Two-way analysis of variance followed by Tukey’s test revealed significant differences in studied environmental variables between habitat types and studied locations, showing that foreland soils still retain particular initial characters to differentiate them from tundra soil.

A New Strain of Bacillus tequilensis CGMCC 17603 Isolated from Biological Soil Crusts: A Promising Sand-Fixation Agent for Desertification Control

In arid and semi-arid desert ecosystems, physical, chemical, and vegetative measures were used to prevent wind erosion. However, studies on the utilization of microbial resources for sand fixation are still limited. To fill this gap, a new strain of Bacillus tequilensis CGMCC 17603 with high productivity of exopolysaccharide (EPS) was isolated from biological soil crusts, and its high-density culture technology and sand-fixing ability were studied. The one-factor-at-a-time approach (OFAT) and Box–Behnken design of CGMCC 17603 showed that the optimum culture conditions were pH 8.5, temperature 31 °C, agitation speed 230 rpm, and inoculation quantity 3%, and the optimum medium was 27.25 g/L glucose, 15.90 g/L yeast extract, and 5.61 g/L MgSO4•7H2O. High-density culture showed that the biomass and EPS yield of CGMCC 17603 increased from 9.62 × 107 to 2.33 × 109 CFU/mL, and from 8.01 to 15.61 g/L, respectively. The field experiments showed that CGMCC 17603 could effectively improve the ability of sand fixation and wind prevention. These results indicated that B. tequilensis, first isolated from cyanobacterial crusts, can be considered as an ideal soil-fixing agent to combat desertification in arid and semi-arid areas.

Induced biological soil crust controls on wind erodibility and dust (PM10) emissions

ABSTRACTInducing biological soil crust (biocrust) development is an appealing approach for dust mitigation in drylands due to the resistance biocrusts can provide against erosion. Using a portable device, we evaluated dust emissions from surfaces either inoculated with biocrust, amended with a plant‐based soil stabilizer, or both at varying wind friction velocities. Four months after application, emissions from all treatments were either indistinguishable from or greater than controls, despite evidence of biocrust establishment. All treatments had greater surface roughness and showed more evidence of entrapment of windblown sediment than controls, factors which may have been partially responsible for elevated emissions. There was a synergistic effect of inoculation and stabilizer addition, resulting in a nearly two‐fold reduction in estimated emissions compared to either treatment alone. Stepwise regression analysis indicated that variables associated with surface crust strength (aggregate stability, penetration resistance) were negatively associated with emissions and variables associated with sediment supply (sand content, loose sediment cover) were positively associated with emissions. With more time to develop, the soil‐trapping activity and surface integrity of biocrust inoculum and soil stabilizer mixtures is expected to increase with the accumulation of surface biomass and enhancement of roughness through freeze–thaw cycles. © 2019 John Wiley & Sons, Ltd.

Biological soil crust succession in deserts through a 59-year-long case study in China: How induced biological soil crust strategy accelerates desertification reversal from decades to years

The regeneration of induced biological soil crusts (IBSCs) is regarded as an effective strategy for combating desertification. Three types of BSCs, namely, cyanobacterial, lichen and moss, are well-accepted as the main succession phases and are hypothesized to represent a continuous process. Herein, natural BSCs (NBSCs) and IBSCs with accurate ages from a 59-year-long field study were investigated to understand the entire BSC succession process. Shifts in nutrient levels, microbial composition and ecological functions suggested that cyanobacterial inoculation successfully accelerated BSC succession from decades to years by promoting the microbial multifunctions related to carbon and nitrogen fixation. The four state transitions of the BSC community accompanied by the turn-over of carbon and nitrogen fixators provide clues to the factors restricting the recovery process and climax of arid ecosystems. This study provides the first description of the continuous BSC succession, comprehensively discusses the mechanisms of BSC formation and succession and provides important guides for selection of strategies for the engineering reversals of desertification.

Development of fungal community is a potential indicator for evaluating the stability of biological soil crusts in temperate desert revegetation

Development of community compositional and functional gene structure of fungi in biological soil crusts (BSCs) of different successional stages in the Tengger Desert, China, was assessed using Illumina MiSeq sequencing and GeoChip analysis, respectively. Fungal diversity and abundance significantly increased during 60 years of succession, and reached close to the highest level in the late BSC development, corresponding to those in natural habitats. Principal coordinate analysis showed that the BSC fungal communities in 60-year-old revegetation and natural vegetation clustered together, when compared with short-term revegetation. Furthermore, the diversity and relative abundance of fungal functional genes involved in biogeochemical cycling and stress response in dominant phyla reached the highest level after 60 years of BSC development, indicating that this period is an important landmark for fungal community and function. Higher functional and compositional resilience in 60-year-old BSCs implied a higher level of stability of the aggregated BSC ecosystem functions. Thus, the stability of BSC ecosystems could be estimated indirectly based on the development of fungal community, and at least 60 years might be needed for the steady state of BSCs in temperate desert zones without mechanical disturbance.

Different types of biocrusts affect plant communities by changing the microenvironment and surface soil nutrients in the Qinghai-Tibetan Plateau

Biocrusts (biological soil crusts), which impact plant community characteristics and soil properties, are an important feature of soil surface in terrestrial ecosystem and called ecosystem engineers in arid and semi-arid habitats. The Qinghai-Tibet Plateau is located in arid and semi-arid regions, and the information on how biocrusts play a role in this ecosystem is still rare. In this study, the effects of different types of biocrusts (lichen-moss crusts, moss crusts, and bare ground as control) on plant diversity and soil physicochemical properties were evaluated and the key environmental factors associated with biocrust characteristics were analyzed in alpine steppe. The results showed that biocrusts affected the structure and diversity of plant community. The lichen-moss crusts were linked with lower plant diversity and plant species richness in degraded alpine steppe in the Qinghai-Tibetan Plateau. The cover of lichen crusts was positively correlated with plant cover while the cover and thickness of moss crusts were negatively correlated with plant cover. Moss crusts significantly reduced soil temperature and soil moisture content. Biocrusts significantly reduced the pH values of soil surface layer (0–1 cm) and deeper layer (5–10 cm). Soil total C (78.10 ± 6.53 g/kg), and total N (5.05 ± 0.21 g/kg) were highest in the soil surface layer (0–1 cm) where lichen-moss crusts were present. Our results indicated that the different types of biocrusts affect plant communities by changing the microenvironment and soil nutrients in the Qinghai-Tibetan Plateau. Further studies on the relationships between soil, biocrusts, and plants on a larger scale in the Qinghai-Tibetan Plateau are necessary.

Effect of preconditioning to the soil environment on the performance of 20 cyanobacterial strains used as inoculum for biocrust restoration

Biological soil crusts are complex communities of organisms that develop on the top layer of dryland soils where they enhance important ecosystem services, including soil fertility and protection from erosion. Regrettably, a range of human activities such as cattle grazing, off‐road driving, hiking, and global warming result in significant deterioration of biocrust cover and their associated services. This scenario has prompted efforts to develop effective biocrust restoration strategies, which often involve the production of biocrust inoculum, both in greenhouse and in laboratory settings. Sometimes this inoculum is preconditioned in a process of “hardening” at considerable expense and effort in order to improve its fitness under harsh field conditions. But the positive effects of such hardening procedures have yet to be rigorously demonstrated. Here, we compared the growth performance of 20 cultured strains of biocrust cyanobacteria in outdoor tests on native soils as a function of preconditioning regimes consisting of increasingly high exposure to solar radiation, temperature and illumination daily variability, and recurrent wet‐dry cycles. Preconditioning improved performance in 13 out of 20 strains, particularly among pioneer crust‐forming Microcoleus spp. (eight out of eight). Improvements were variable among heterocystous strains (three out of four Scytonema spp., two out of four Tolypothrix spp., and none out of four Nostoc spp.). Based on these results, we recommend the inclusion of preconditioning treatments to increase inoculum survival rate and speed of cyanobacterial biocrust recovery in restoration of dryland soils.

Grazing-Induced Changes to Biological Soil Crust Cover Mediate Hillslope Erosion in Long-Term Exclosure Experiment

Dryland ecosystems are particularly vulnerable to erosion generated by livestock grazing. Quantifying this risk across a variety of landscape settings is essential for successful adaptive management, particularly in light of a changing climate. In the Upper Colorado River Basin, there are nearly 25 000 km2 of rangelands with underlying soils derived from Mancos Shale, an erodible and saline geologic parent material. Salinity is a major concern within the Colorado River watershed, much of which is attributed to runoff and leaching from Mancos Shale deposits. In a 60-yr paired-watershed experiment in western Colorado, we used silt fences to measure differences in saline hillslope erosion, including both total sediment yield and concentrations of primary saline constituents (Na and Se), in watersheds that were either exposed to grazing or where livestock was excluded. After accounting for the strong effects of soil type, slope, and antecedent precipitation, we found that grazing increased sediment loss by ≈50% across our 8-yr time series (0.1–1.5 tn ha−1), consistent with levels reported at the watershed scale in early published work from studies at the same location. Eroded sediment Se levels were low and unaffected by grazing history, but Na concentrations were significantly reduced on grazed hillslopes, likely due to depletion of surface Na in soils exposed to chronic soil disturbance by livestock. Variable selection and path analysis identified that biological soil crust (BSC) cover, more than any other variable, explained the differences in sediment yields between grazed and ungrazed watersheds, partially through the enhancement of soil aggregate stability. Our results suggest that BSC cover should be granted heightened consideration in rangeland decision support tools (e.g., state-and-transition models) and that measures to reduce surface disturbance from livestock such as altering the timing or intensity of grazing may be effective for reducing downstream impacts.

Learning representations of microbe-metabolite interactions.

Integrating multi-omics datasets is critical for microbiome research, but multiple statistical challenges can confound traditional correlation techniques. We solve this problem by using neural networks to estimate the conditional probability that each molecule is present given the presence of each specific microbe. We show with known environmental (desert biological soil crust wetting) and clinical (cystic fibrosis lung) examples, our ability to recover microbe-metabolite relationships, and demonstrate how the method can discover relationships between microbially-produced metabolites and inflammatory bowel disease.

Surface Stability in Drylands Is Influenced by Dispersal Strategy of Soil Bacteria

AbstractMicrobial adaptations for survival and dispersal may directly influence landscape stability and potential for dust emission in drylands where biological soil crusts (biocrusts) protect mineral soil surfaces from wind erosion. In the Lake Eyre basin of central Australia we operated a wind tunnel on sandy soils and collected the liberated material, which was subjected to DNA sequencing to identify the microbial community composition. Microbial composition of entrained dust was compared with that of the source sand dune soil in addition to nearby claypan and nebkha soils and water channels that together form a recycling sediment transport system. Wind was found to preferentially liberate 359 identified taxa from sand dunes, whereas 137 identified taxa were found to resist wind erosion. Water channel communities included many taxa in common with the soil samples. We hypothesize that the ease with which soil microbes become airborne is often linked to whether the organism is adapted for dispersal by wind or vegetative growth and that biocrust organisms found in water channels may sometimes use a fluvial dispersal strategy, which exploits rare flooding events to rapidly colonize vast pans that are common in drylands. We explain likely geomorphic implications of microbial dispersal strategies which are a consequence of organisms engineering the environment to provide their particular needs. By identifying microbes fitting expectations for these dispersal strategies based on differential abundance analyses, we provide a new perspective for understanding the role of microbiota in landscape stability.

Comparison of Microphototrophic Communities Living in Different Soil Environments in the High Arctic

The Arctic region undergoes rapid climate change resulting in soil warming with consequent changes in microbial community structure. Therefore, it is important to gain more knowledge on the pioneer photosynthetic microorganisms and their relations to environmental factors. Here we provide a description of the community composition of microbial phototrophs in three different types of soils in the High Arctic (Svalbard): vegetated soil at a raised marine terrace, biological soil crust (BSC) at high elevation, and poorly-developed BSC in a glacier foreland. The studied sites differed from each other in microclimatic conditions (soil temperature and soil water content), soil chemistry and altitude. Combining morphological (cell biovolume) and molecular methods (NGS amplicon sequencing of cyanobacterial 16S rRNA and eukaryotic 18S rRNA sequences of isolates), we studied the diversity and biovolume of cyanobacteria and eukaryotic microalgae. The results showed that cyanobacteria prevailed in the high altitude BSC as well as in pioneering BSC samples in glacier foreland though with lower biomass. More specifically, filamentous cyanobacteria, mainly Leptolyngbya spp., dominated the BSCs from these two localities. In contrast, coccoid microalgae (green and yellow-green algae) had higher biovolume in low altitude vegetated soils. Thus, the results of this study contribute to a better understanding of microphototrophic communities in different types of Arctic soil environments.

Comparative metagenomics of two distinct biological soil crusts in the Tengger Desert, China

Biological soil crusts (biocrusts) are widely distributed in arid and semi-arid environments worldwide. The microbiome metabolic pathways of biocrusts contribute to important biogeochemical processes that improve the physicochemical properties of the surface soil. However, the differences in microbial processes among different types of biocrusts have been poorly studied by metagenomic analyses. In this study, we compared two types of biocrusts (bacterial-dominated biocrusts and moss-dominated biocrusts) using shotgun metagenomic sequencing. Our results showed that Actinobacteria was the most abundant phylum in the microbiomes of bacterial and moss biocrusts, even though the two biocrusts differed in the composition of the following other abundant phyla Proteobacteria, Acidobacteria, Cyanobacteria, Planctomycetes and Bacteroidetes. The profile of the C- and N- related metabolic pathways of the metagenome differed between the bacterial and moss biocrusts. The results showed that the genes encoding carbon monoxide dehydrogenase were more abundant than the gene encoding the ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) involved in the Calvin cycle, which is actually the main metabolic pathway for carbon fixation in both biocrusts. Low diversity in N2 fixation pathways appears to be a distinguishing feature of biocrust microbiomes, while nitrogen reduction dominated the metabolic networks of the two biocrusts. The microbiome of bacterial biocrusts rich in assimilatory nitrate reduction genes, while the microbiome of moss biocrusts was rich in dissimilatory nitrate reduction genes. Amongst the (bio-)chemical parameters it is total organic carbon(TOC) that differentiates between the bacterial and moss biocrusts. Our study suggests that the biocrust types have significant effects on the TOC content and taxonomic, gene and metabolic diversity.

Development of archaeal communities in biological soil crusts along a revegetation chronosequence in the Tengger Desert, north central China

Archaea are major contributors to biogeochemical cycles and energy metabolism among soil microorganisms under extremely acidic and high-temperature conditions, however, the biodiversity and ecological function of archaea in biological soil crusts (BSCs) of desert ecosystems are not fully understood. Here, we used Illumina MiSeq sequencing and microbial functional gene array (GeoChip 5.0) to test the following hypotheses: (1) the composition and function related to biogeochemical cycles of the archaeal community would change significantly in the development process of BSCs; and (2) the key factors driving these changes may be soil biogeochemical properties. The results showed that the diversity, abundance, and functional potential of the archaeal community showed their highest levels in 5-year-old BSCs. The dominant phyla were Thaumarchaeota, Euryarchaeota, and an unclassified phylum in the archaeal community during BSC succession. The functional genes of the archaeal community were mainly involved in carbon (C) and nitrogen (N) cycles, and the functions of the three dominant phyla were complementary in these cycles. Moreover, redundancy analysis showed that soil biogeochemical properties were negatively related to the composition and function of the archaeal community during BSC succession, and the soil C:N ratio might be the major limiting factor. These results provided evidences for our hypotheses and revealed that the archaeal community played an important ecological role in the early development stage of BSCs, and might be pioneer species of soil microbial communities during BSC succession.