Biocrust Development Research Articles

Grazing disturbance reduces biocrust-related cyanobacteria and N-fixer abundance but increases bacterial diversity: Implications for biocrust restoration in degraded drylands

Overgrazing is a major driver of dryland degradation, however, so far, there is limited understanding on how this process affects biocrust-related microbial community, and especially how the key groups respond to grazing disturbance. In this study, quantitative polymerase chain reaction (qPCR) and high throughout sequencing technologies were used to investigate the bacterial community abundance and diversity in the Horqin Sandland (China) experiencing different livestock grazing disturbances, in order to examine whether a shift in bacterial community (in particular the key biocrust components, cyanobacteria) was involved, and how this was related to biocrust development and altered soil carbon and nitrogen level. Our results revealed that a clear heterogeneous soil bacterial community was associated with grazing disturbance, which inhibited biocrust development. The decreased photosynthetic cyanobacterial abundance (81.81 % in relative abundance and 98.83 % in absolute abundance) and nitrogen-fixing genes (87.72 %), associated with the lower total carbon and nitrogen content (P<0.05), illustrated a low soil carbon and nitrogen-fixing capability and nutrient level in the grazing-disturbed soils. In particular, a switch of nitrogen-fixing dominance from cyanobacteria to proteobacteria was induced by the grazing disturbance. Compared to the grazing-disturbed soils, higher dominant cyanobacterial operational taxonomic units (OTUs) (especially the species of Nostoc and Scytonema) and lower bacterial diversity (e.g., Shannon, Ace, and Chao index) were observed in the undisturbed biocrust soils, highlighting that the dominants rather than diversity played more important roles in biocrust development. Collectively, our results demonstrate that cyanobacteria are very sensitive (even more than others, e.g., proteobacteria and actinobacteria) to grazing disturbance, therefore, we propose that cyanobacterial inoculation is likely an effective approach to supplement soil cyanobacterial abundance, which is expected to induce biocrust development and increase carbon and nitrogen level in the disturbed drylands.

Biological soil crust elicits microbial community and extracellular polymeric substances restructuring to reduce the soil erosion on tropical island, South China Sea

Soil erosion stands as the preeminent environmental concern globally, attaining heightened significance, particularly within islands where land resources prove notably scarce. Biological soil crusts, referred to as biocrusts, assume a pivotal ecological role in soil conservation. Notably, they augment the horizontal stability of the substrate through the exudation of microbial extracellular polymeric substances (EPS), thereby shielding the soil against shear stress, exemplified in the form of water erosion. While extant research has delved into the anti-erosion mechanisms of biocrusts in arid landscapes, a conspicuous lacuna persists in the exploration of coral island environments. In this study, we collected and assessed 30 samples encompassing dark biocrusts, light biocrusts, and bare soil to scrutinize the potential anti-erosion efficacy of tropical coral island biocrusts within the South China Sea. Employing a cohesive strength meter, we quantified soil shear stress across various stages of biocrust development, revealing a discernible enhancement in soil erosion resistance during the formation of biocrusts. Relative to the exposed bare soil, the soil shear stress exhibited an escalation from 0.33 N m−2 to 0.61 N m−2 and 1.31 N m−2 in the light biocrusts and dark biocrusts, respectively. Mechanistically, we assayed microbial EPS contents, exposing a positive correlation between EPS and soil anti-erodibility, encompassing extracellular protein and polysaccharide. Concurrently, bacterial abundance displayed a significant augmentation commensurate with biocrust formation and development. In pursuit of elucidating the origin of EPS, high-throughput amplicon sequencing was executed to identify microorganisms contributing to biocrust development. Correlation analysis discerned Cyanobacteria, Chloroflexi, Deinococcota, and Patescibacteria as potential microbials fostering EPS production and fortifying erosion resistance. Collectively, our study presents the first evidence that biocrust from tropical coral reef island in the South China Sea promotes resistance to soil erosion, pinpointing key EPS-producing microbials against soil erosion. The findings would provide insights for island environment restoration.

Successional development of the phototrophic community in biological soil crusts, along with soil formation on Holocene deposits at the Baltic Sea coast

Harsh environmental conditions form habitats colonized by specialized primary microbial colonizers, e.g., biological soil crusts (biocrusts). These cryptogamic communities are well studied in drylands but much less in temperate coastal dunes, where they play a crucial role in ecological functions. Following two dune chronosequences, this study highlights the successional development of the biocrust’s community composition on the Baltic Sea coast. A vegetation survey, followed by morphological species determination, was conducted. Sediment/soil cores of the different dune types were analyzed to uncover the potential impacts of the biocrust community on initial soil formation processes, with special emphasis on biogeochemical phosphorous (P) transformations. Biocrust succession was characterized by a dune type-specific community composition, shifting from thinner algae-dominated biocrusts in dynamic dunes to more stable moss-dominated biocrusts in mature dunes. The change in the biocrust community structure was accompanied by an increase in Chl a, water, and organic matter content. In total, 25 algal and cyanobacterial species, 16 mosses, and 26 lichens across all sampling sites were determined. The pedological characterization of these cores elucidated initial processes of soil genesis, such as decalcification, acidification, and the accumulation of organic matter with dune and biocrust development. Furthermore, the chemistry of iron (Fe)-containing compounds such as the Fedithionite/Fetotal ratios confirmed mineral weathering and the beginning of soil profile development. The biocrusts accumulated P over time, while the P content in the underlying sediment did not change. That implies that biocrusts take up P from the geological parent material in the dunes, thereby accumulating available P in the ecosystem, which gets transferred into subsoil horizons through leaching or redeposition. The relative proportion of the bioavailable P pool (56% to 74% of Pt) increased with dune succession. That happened at the expense of more stable bound P, which was transformed into labile P. Thus, the level of plant available P along the dune chronosequences increased due to the microbial activity of the biocrust organisms. It can be concluded that biocrusts of temperate coastal dunes play a crucial role in maintaining their habitat by accumulating nutrients and organic matter, supporting soil development and subsequent vegetation.

Dynamics in eukaryotic algal communities regulate bacterial and fungal communities as biocrusts develop in a temperate desert in Central Asia

Abstract Eukaryotic algae, as the primary group of photosynthetic autotrophs, exert a significant influence on the development and functions of biological crusts in dryland ecosystems. Despite their importance, there are substantial knowledge gaps on the composition of eukaryotic algal communities and their effects on the distributions of bacteria and fungi in dryland soils. This study examined the eukaryotic algal community along a successional sequence of biocrusts in the Gurbantunggut desert, while also investigating their patterns of co‐occurrence with bacteria and fungi through high‐throughput sequencing and bioinformatic analyses. The results showed that nitrogen and phosphorus levels played a crucial role in the regulation of changes in the abundance and composition of the algal community. In particular, changes in the structure of the algal community arise primarily from fluctuations in the main species, rather than from loss and appearance of species during the biocrust succession. The accumulation of nitrogen and phosphorus in the biocrust was associated with the decrease in the relative abundance of Chlorophyta. The results also indicated that eukaryotic algae played an important role in the affecting bacterial and fungal communities and significantly improved the stability of the microbial community, reflected by the robustness of co‐occurrence networks. The network analysis further indicated that eukaryotic algae affected the stability of microbial co‐occurrence networks either by acting as keystone taxa or associating with the keystone bacterial and fungal taxa. These findings reveal a clear mechanism by which soil nitrogen and phosphorus levels affected the composition of eukaryotic algae communities and further regulated bacterial and fungal communities during biocrust development, providing valuable information on the development and functional execution of biocrusts in dryland ecosystems. Read the free Plain Language Summary for this article on the Journal blog.

The development of the biological soil crust regulates the fungal distribution and the stability of fungal networks.

The heterogeneous composition of fungi plays an indispensable role in the foundation of the multifunctionalities of ecosystems within drylands. The precise mechanisms that govern fluctuations in soil fungal assemblages in dryland ecosystems remain incompletely elucidated. In this study, biological soil crusts (biocrusts) at different successional stages in the Gurbantunggut Desert were used as substrates to examine the characteristics and driving factors that influence fungal abundance and community dynamics during biocrust development using qPCR and high-throughput sequencing of the ITS2 region. The findings showed that the physicochemical properties changed significantly with the development of biocrusts. In particular, total nitrogen increased 4.8 times, along with notable increases in ammonium, total phosphorus (2.1 times) and soil organic carbon (6.5 times). Initially, there was a rise in fungal abundance, which was subsequently followed by a decline as the biocrust developed, with the highest abundance detected in lichen crust (2.66 × 107 copies/g soil) and the lowest in bare sand (7.98 × 106 copies/g soil). Ascomycetes and Basidiomycetes emerged as dominant phyla, collectively forming 85% of the fungal community. As the biocrust developed, noticeable alterations occurred in fungal community compositions, resulting from changes in the relative proportions of Dothideomycetes, Lecanoromycetes and unclassified ascomycetes. Nitrogen, phosphorus, organic carbon content, and pH of biocrusts were identified as direct or indirect regulators of fungal abundance and community structure. The complexity of fungal networks increased as biocrusts developed as revealed by network analysis, but reduced in the stability of fungal communities within algal and lichen crusts. Keystone species within the fungal community also underwent changes as biocrust developed. These results suggested that shifts in interspecies relationships among fungi could further contribute to the variation in fungal communities during the development of biocrusts.

Deterministic processes influence bacterial more than fungal community assembly during the development of biological soil crusts in the desert ecosystem.

Biological soil crusts (biocrusts) constitute a crucial biological component of the soil surface in arid and semi-arid ecosystems. Understanding the variations in soil microbial community assembly across biocrust successional stages is essential for a deeper comprehension of microbial biodiversity and desert ecosystem functioning. However, knowledge about the mechanisms of microbial community assembly and the factors influencing its development remains limited. In this study, we utilized amplicons sequencing to assess the compositions of bacterial and fungal communities in bare sand and three types of biocrusts (light cyanobacterial biocrusts, dark cyanobacterial biocrusts, and moss crusts). Subsequently, we analyzed the ecological processes shaping microbial community composition and structure, along with the influencing factors. Our results revealed a significant increase in bacterial diversity and no significant changes in fungal diversity during biocrust development. The relative abundances of the copiotrophic bacteria (e.g., Actinobacteria, Acidobacteria, and Bacteroidetes) showed significant increases, while oligotrophic bacteria (e.g., Proteobacteria and Firmicutes) decreased over time. Moreover, the relative abundances of Ascomycota, which exhibit strong resistance to adverse environmental conditions, significantly decreased, whereas Basidiomycota, known for their ability to degrade lignin, significantly increased throughout biocrust development. Additionally, stochastic processes (dispersal limitation and drift) predominantly drove the assemblies of both bacterial and fungal communities. However, the relative importance of deterministic processes (homogeneous selection) in bacterial assembly increased during biocrust development. Structural equation modeling indicated that bacterial community assembly was primarily related to soil water content, whereas fungal community assembly was primarily related to total organic carbon. These findings provide a scientific foundation for investigating the formation and development of biocrusts, and further insights into the conservation and sustainable management of biocrust resources under future climate change scenarios.

Potential mechanisms of soil nitrogen content heterogeneity associated with biocrust development in drylands

AbstractBiological soil crusts (biocrusts) are complex communities of micro‐ and macro‐organisms dwelling at the soil surface in dryland regions worldwide, which contribute to important ecological functions in these areas. Biocrusts may reach different developmental stages, associated to autogenic succession of specific phototrophic organisms. However, notwithstanding the large amount of existing literature, little is known regarding the relationship between biocrust stages of development and soil nutrient dynamics. In this opinion paper, we specifically focused on soil nitrogen, and compared the total nitrogen content and potential nitrogenase activity of different developmental types of biocrust (‐covered) soils. Based on published reports, we looked at a possible relationship between nitrogen content at the soil surface and biocrust development, discussing the potential mechanisms leading to the observed soil nitrogen content heterogeneity. The results showed that a higher nitrogen content remained associated to the presence of moss‐dominated biocrusts, and this biocrust morphotype was characterized by a lower potential nitrogenase activity compared to the cyanobacteria‐ and/or lichen‐dominated biocrusts. We hypothesized that these seemingly contradictory findings might be attributed to three potential mechanisms: nitrogen inheritance, nutrient retention and nutrient transfer, which we hereby examined one by one. Altogether, our opinion supports the theory of biocrust succession from incipient cyanobacteria‐dominated stages to more ‘mature’ stages dominated by mosses. We stress how the heterogeneous distribution of soil nitrogen, which is closely related with biocrust development and community types, eventually affects regional and even global nitrogen dynamic and storage.

Enhancing Biocrust Development and Plant Growth through Inoculation of Desiccation-Tolerant Cyanobacteria in Different Textured Soils.

In recent years, there has been a burgeoning interest in the utilization of cyanobacteria for the purpose of land rehabilitation via enhancements in soil fertility, prevent erosion, and counter desertification. This study evaluated the ability of Nostoc calcicola BOT1, Scytonema sp. BOT2, and their consortia to form biocrusts on the substrate of coarse sand, fine sand, and loamy soil. A nutrient- and water-deficient substrate was inoculated with cyanobacteria to facilitate biocrust formation and evaluate their impact on agriculture. Cyanobacteria inoculation resulted in significant improvements in soil fertility, especially in coarse and fine sand, which initially had the lowest fertility. The findings of this investigation underscore that the consortium of cyanobacteria exhibited greater efficacy than individual strains in enhancing soil fertility and stimulating plant growth. The loamy soil treated with the consortium had the highest plant growth across all soil types, in contrast to the individual strains. The consortium of cyanobacteria showed promising results in promoting biocrust formation and fostering rice seedling growth in fine sand. This study provides empirical evidence supporting the potential utility of cyanobacterial consortia as a valuable tool for the rehabilitation of degraded land. Furthermore, the results indicate that cyanobacterial species can persist in soil environments even following prolonged periods of desiccation.

Erratum to “Rapid artificial biocrust development by cyanobacterial inoculation and clay amendment”

Erratum to “Rapid artificial biocrust development by cyanobacterial inoculation and clay amendment”

Soil depths and developmental stages of biological soil crusts are more important than shrub cover in structuring prokaryotic communities

The influence of microhabitat factors on prokaryotic communities within desert ecosystems, particularly those residing in biological soil crusts (biocrusts), remains poorly understood. This study aimed to elucidate the relative importance of different microhabitats, including soil depths, biocrust developmental stages, and shrub cover, in shaping soil prokaryotic communities. To achieve this, we conducted an in-depth investigation of soil prokaryotic communities using high-throughput amplicon sequencing in the Tengger desert, China. Our results showed that difference of soil properties, prokaryotic alpha, beta diversities and abundances of taxa and functional groups primarily differed between soil depths and among biocrust developmental stages. Furthermore, the impact of shrub cover on the aforementioned parameters was found to be modified by biocrust development. Specifically, we observed higher soil nutrient levels in the upper biocrust layer compared to the subsoil, with a consistent increasing trend during biocrust development in both soil layers. Conversely, soil pH displayed contrasting patterns. Prokaryotic alpha diversity exhibited a V-shaped pattern with biocrust development, initially decreasing and then increasing, and was higher in the subsoil compared to the biocrust layer. Additionally, although prokaryotic alpha diversity showed differences between shrub cover or not, the specific effect depended on biocrust stages. Cyanobacteria, phototrophic and nitrogen-fixing prokaryotes were more abundant in the upper biocrust layer, following a unimodal pattern with biocrust development, initially increasing, and then decreasing; while Actinobacteriota and Acidobacteriota showed higher abundance in the subsoil, with varying trends between the two soil depths during biocrust development. Soil pH and total P emerged as key regulators of prokaryotic communities across different microhabitats. This study contributes to our comprehensive understanding of the complex dynamics governing prokaryotic communities in desert ecosystems.

Microbiome convergence and deterministic community assembly along successional biocrust gradients on potash salt heaps.

Potash mining, typically performed for agricultural fertilizer production, can create piles of residual salt waste that are ecologically detrimental and difficult to revegetate. Biological soil crusts (biocrusts) have been found growing on and around these heaps, suggesting resilience to the hypersaline environment. We set out to understand the community dynamics of biocrust formation by examining two succesionary salinity gradients at historical mining sites using a high throughput amplicon sequencing. Bare heaps were distinct, with little overlap between sites, and were characterized by high salinity, low nutrient availability, and specialized, low diversity microbial communities, dominated by Halobacteria, Chloroflexia, and Deinococci. 'Initial' stages of biocrust development were dominated by site-specific Cyanobacteria, with significant overlap between sites. Established biocrusts were the most diverse, with large proportions of Alphaproteobacteria, Anaerolineae, and Planctomycetacia. Along the salinity gradient at both sites, salinity decreased, pH decreased, and nutrients and Chlorophyll a increased. Microbiomes between sites converged during succession and community assembly process analysis revealed biocrusts at both sites were dominated by deterministic, niche-based processes; indicating a high degree of phylogenetic turnover. We posit early cyanobacterial colonization is essential for biocrust initiation, and facilitates later establishment of plant and other higher-level biota.

Post-fire wood mulch negatively affects the moss biocrust cover and its positive effects on microbial diversity in a semi-arid Mediterranean forest

Mulches are highly effective in mitigating the risk of erosion generated after wildfires in fire-prone ecosystems. Despite being a technique commonly used, it remains completely unexplored how mulches interact with the positive effects of the emergent moss biocrust on the recovery and resilience of soils and their microbial communities. For this purpose, the effects of wood-based mulch were assayed on the soil stability and moisture improvement, the nutrient inputs, and the response of microbial biomass, activity, composition, and diversity. Soils were studied after one year of wood mulch application at two rates representing possible scenarios, “Rate 1” (65 % of soil cover), and “Rate 2” (100 % of cover), and “Control” soils without mulch. The biocrust development had a positive impact on soil aggregate stability and moisture retention before mulch application. However, one year after the mulch application the biocrust cover was drastically inhibited, especially at the highest rate of mulch. Independently of the biocrust presence, soils at Rate 1 registered a tendency to higher nitrogen content, available phosphorous, basal respiration, and microbial biomass carbon, suggesting an incipient recovery of soil conditions and soil functionality. However, the microbial community composition became more homogeneous and less diverse under the mulch presence (regardless of the application rate), and the positive effect of moss biocrust emergence on the microbial diversity was diluted after one year. The fungal community was particularly sensitive to the wood mulch presence, increasing in richness in response to fresh wood incorporation to soils, in particular saprotrophs and yeasts. The fungal and bacterial compositional shifts after the mulch application reveal an incipient wood decomposition stage, but the transitory loss in beta diversity after the moss biocrust suppression warns about the necessity of including the microbial diversity information into post-fire management planning. Studying the effects of forest management on the above and belowground soil communities is essential to understanding the resistance and resilience of semi-arid forests to the increasing intensity and severity of wildfires.

Biological soil crusts as a major ecosystem component in sandization areas of the Brazilian Pampa

In the Brazilian Pampa, vegetation disturbance and soil degradation led to an expansion of sediment remobilization areas, a process locally termed as sandization. Transported sands generate severe environmental problems and hamper the growth of vegetation. However, parts of these sandization areas are quickly covered by biological soil crusts (biocrusts), which have not been investigated in this biome before.This study describes biocrust occurence in sandization areas of the Brazilian Pampa for the first time and analyses their distribution patterns related to the local topography. We studied biocrusts at two research sites where their presence appeared to be essential for soil protection. First, the occurrence of different biocrust types were assessed and a taxonomic survey was conducted. Second, UAV-based imagery was created and biocrusts were classified, using a random forest approach to understand the relation of their abundance to topography.We observed that biocrusts occurred widely in areas prone to sandization with an approx. 25% distribution on the land surface. They are mostly dominated by cyanobacteria and secondarily by bryophytes. Among the observed genera, the cyanobacterial genus Stigonema sp. was dominating in both study sites. Campylopus pilifer was the dominating moss species. The mapped biocrusts represented all major morphological types and were classified as rolling, pinnacled, rugose, and smooth crusts. Local topography was a major driver for biocrust distribution, but also the establishment of vascular plants. Slope and aspect had a strong influence on biocrust development, but the presence of protective topographic positions against atmospheric influences most prominently facilitated their occurrence.This pilot study proves that biocrusts can potentially play a key role as ecosystem engineers in the Brazilian Pampa with a positive effect on general vegetation growth and soil-stabilization. In this biome, however, they have been largely overlooked compared to other areas globally. Thus, biocrusts need to be further studied and their effects considered in land management to constrain further soil degradation.

Rapid artificial biocrust development by cyanobacterial inoculation and clay amendment

AbstractThe establishment of biological soil crusts is widely perceived as a main strategy to improve the ecological environment in arid and semi‐arid regions. However, artificial biocrusts fail to withstand environmental stresses when using traditional methods for initial establishment. Hence, in this study, kaolin, a common clay mineral, was introduced as a biocrust stabilizer by mixing at different mass ratios with Microcoleus steenstrupii for sand inoculation. The results showed that the addition of kaolin exhibited a significantly positive effect on promoting biocrust formation and accelerating biocrust development. Moreover, the artificial biocrust from 1:500 (algae: kaolin) inoculant achieved the best performance with coverage of 98%, and top layer thickness of 5.62 mm after 86 days of incubation. The highest contents of chlorophyll a, exopolysaccharides, and soluble protein were also observed in 1:500 mass ratio of algae: kaolin throughout the biocrust development process. As for the water retention performance, the results of contact angle, water drop penetration time (WDPT), and repellency index (RI) illustrated that biocrust improved water utilization in kaolin‐treated groups by delaying the time of water infiltration, especially in 1:500 group. After 86 days post inoculation, a series of common bacteria appeared in the biocrusts such as actinobacteria and acidobacteria, and decomposed metabolites from cyanobacteria as an energy source. This study gains new insights into clay minerals on biocrust development and puts forward a new approach for rapid artificial biocrust establishment to reverse desertification.

Plasma Treatment as a Sustainable Method for Enhancing the Wettability of Jute Fabrics

In this paper, raw jute fabric was subjected to atmospheric pressure dielectric barrier discharge (at 150 or 300 Hz) to enhance its wettability, i.e., capillarity and wetting time. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Field Emission Scanning Electron Microscopy (FE-SEM) were used to assess the changes in the fabrics’ surface chemistry and morphology induced by plasma treatments. The obtained results revealed that both plasma treatments enhanced the wettability of jute fabrics, which could be ascribed to the changes in the fibers’ surface chemistry (the removal of non-cellulosic components, exposure of the cellulose molecules, and oxidation) and morphology (increased roughness due to etching of the surface layers and partial fibrillation). Capillary rise heights increased by approximately 1.8 and 1.9 times, and wetting times were 35 and 34 times shorter 24 h after the plasma treatment at 150 and 300 Hz, respectively. Special attention was given to the aging effect of plasma treatment indicated no significant changes in the fabrics’ capillarity and wetting time after 28 and 7 days, respectively, proving the durability of the effects of plasma treatment. Plasma-treated raw jute fabrics could be used as water-binding geo-prebiotic polysaccharide supports to provide the necessary water for the initial growth of cyanobacterial biocrusts. The lack of moisture is the main constraint in biocrust development after cyanobacterial inoculation. The combination of such water-supportive fabrics and cyanobacterial strains could be used for the rehabilitation of various degraded lands, sediments, and substrates, as well as for air and water pollution control.

Successional Development of the Phototrophic Community in Biological Soil Crusts on Coastal and Inland Dunes.

(1) Biological soil crusts (biocrusts) are microecosystems consisting of prokaryotic and eukaryotic microorganisms growing on the topsoil. This study aims to characterize changes in the community structure of biocrust phototrophic organisms along a dune chronosequence in the Baltic Sea compared to an inland dune in northern Germany. (2) A vegetation survey followed by species determination and sediment analyses were conducted. (3) The results highlight a varying phototrophic community composition within the biocrusts regarding the different successional stages of the dunes. At both study sites, a shift from algae-dominated to lichen- and moss-dominated biocrusts in later successional dune types was observed. The algae community of both study sites shared 50% of the identified species while the moss and lichen community shared less than 15%. This indicates a more generalized occurrence of the algal taxa along both chronosequences. The mosses and lichens showed a habitat-specific species community. Moreover, an increase in the organic matter and moisture content with advanced biocrust development was detected. The enrichment of carbon, nitrogen, and phosphorus in the different biocrust types showed a similar relationship. (4) This relation can be explained by biomass growth and potential nutrient mobilization by the microorganisms. Hence, the observed biocrust development potentially enhanced soil formation and contributed to nutrient accumulation.

Soil-atmosphere fluxes of CO2, CH4, and N2O across an experimentally-grown, successional gradient of biocrust community types.

Biological soil crusts (biocrusts) are critical components of dryland and other ecosystems worldwide, and are increasingly recognized as novel model ecosystems from which more general principles of ecology can be elucidated. Biocrusts are often diverse communities, comprised of both eukaryotic and prokaryotic organisms with a range of metabolic lifestyles that enable the fixation of atmospheric carbon and nitrogen. However, how the function of these biocrust communities varies with succession is incompletely characterized, especially in comparison to more familiar terrestrial ecosystem types such as forests. We conducted a greenhouse experiment to investigate how community composition and soil-atmosphere trace gas fluxes of CO2, CH4, and N2O varied from early-successional light cyanobacterial biocrusts to mid-successional dark cyanobacteria biocrusts and late-successional moss-lichen biocrusts and as biocrusts of each successional stage matured. Cover type richness increased as biocrusts developed, and richness was generally highest in the late-successional moss-lichen biocrusts. Microbial community composition varied in relation to successional stage, but microbial diversity did not differ significantly among stages. Net photosynthetic uptake of CO2 by each biocrust type also increased as biocrusts developed but tended to be moderately greater (by up to ≈25%) for the mid-successional dark cyanobacteria biocrusts than the light cyanobacterial biocrusts or the moss-lichen biocrusts. Rates of soil C accumulation were highest for the dark cyanobacteria biocrusts and light cyanobacteria biocrusts, and lowest for the moss-lichen biocrusts and bare soil controls. Biocrust CH4 and N2O fluxes were not consistently distinguishable from the same fluxes measured from bare soil controls; the measured rates were also substantially lower than have been reported in previous biocrust studies. Our experiment, which uniquely used greenhouse-grown biocrusts to manipulate community composition and accelerate biocrust development, shows how biocrust function varies along a dynamic gradient of biocrust successional stages.

Biocrust Amendments to Topsoils Facilitate Biocrust Restoration in a Post-mining Arid Environment.

Soil cryptogamic biocrusts provide many ecological functions in arid zone ecosystems, though their natural reestablishment in disturbed areas is slow. Accelerating reestablishment of biocrusts may facilitate the establishment of vascular plant communities within the timeframes of restoration targets (typically 5–15 years). One technique is to inoculate the soil surface using slurries of biocrust material harvested from another site. However, this is destructive to donor sites, and hence the potential to dilute slurries will govern the feasibility of this practice at large spatial scales. We conducted a replicated experiment on a disturbed mine site to test the individual and combined effects of two strategies for accelerating soil cryptogamic biocrust reestablishment: (1) slurry inoculation using biocrust material harvested from native vegetation; and (2) the use of psyllium husk powder as a source of mucilage to bind the soil surface, and to potentially provide a more cohesive substrate for biocrust development. The experiment comprised 90 experimental plots across six treatments, including different dilutions of the biocrust slurries and treatments with and without psyllium. Over 20 months, the reestablishing crust was dominated by cyanobacteria (including Tolypothrix distorta and Oculatella atacamensis), and these established more rapidly in the inoculated treatments than in the control treatments. The inoculated treatments also maintained this cover of cyanobacteria better through prolonged adverse conditions. The dilute biocrust slurry, at 1:100 of the biocrust in the remnant vegetation, performed as well as the 1:10 slurry, suggesting that strong dilution of biocrust slurry may improve the feasibility of using this technique at larger spatial scales. Psyllium husk powder did not improve biocrust development but helped to maintain a soil physical crust through hot, dry, and windy conditions, and so the potential longer-term advantages of psyllium need to be tested.

Effects of moss biocrusts on soil-microbe-ectoenzyme stoichiometric characteristics in a subtropical area

The formation and development of biological soil crusts (biocrusts) potentially affect the cycles and stoichiometric characteristics of soil carbon (C), nitrogen (N), and phosphorus (P). However, it is still unclear how soil microbes adapt to such changes. In this study, we examined the effects of moss-dominated biocrusts coverage (0, 1%-20%, 20%-40%, 40%-60%, 60%-80%, and 80%-100%) on soil physicochemical properties, soil microbial biomass, and ectoenzyme activities [β-1, 4-glucosidase (BG), β-1, 4-N-acetyl glucosidase (NAG), acid phosphatase (AP)] in two soil layers (0-5 and 5-10 cm) in the Three Gorges Reservoir area, as well as the covariations of soil-microbe-ectoenzyme C:N:P stoichiometry. The results showed that biocrust development significantly increased soil clay content, water stable aggregates, soil C, N, P contents, and significantly decreased soil bulk density and sand content. Microbial biomass C, N, P and ectoenzyme activities were significantly increased with increasing biocrust coverage. Soil depth did not affect soil physicochemical properties and C:N:P, but significantly affected microbial biomass, ectoenzyme activities, BG:AP and NAG:AP. Soil C, N and P contents were significantly positively correlated with microbial biomass and ectoenzyme activities, negatively correlated with BG:NAG, while positively correlated with NAG:AP, but had no significant correlation with microbial biomass C:N:P. There was no significant correlation between soil-microbe and microbial-ectoenzyme C:N:P. BG:NAG:AP decreased gradually with the increase of C:N:P stoichiometric imbalance between microbe and soil. This study indicated that the microbial metabolism was co-limited by N and P and with stronger P limitation. Microbes could maintain homeostasis by adjusting their own biomass and ectoenzyme C:N:P to adapt to changes in soil ecological stoichiometry driven by biocrust development.

Microbial Communities in Biocrusts Are Recruited From the Neighboring Sand at Coastal Dunes Along the Baltic Sea.

Biological soil crusts occur worldwide as pioneer communities stabilizing the soil surface. In coastal primary sand dunes, vascular plants cannot sustain due to scarce nutrients and the low-water-holding capacity of the sand sediment. Thus, besides planted dune grass, biocrusts are the only vegetation there. Although biocrusts can reach high coverage rates in coastal sand dunes, studies about their biodiversity are rare. Here, we present a comprehensive overview of the biodiversity of microorganisms in such biocrusts and the neighboring sand from sampling sites along the Baltic Sea coast. The biodiversity of Bacteria, Cyanobacteria, Fungi, and other microbial Eukaryota were assessed using high-throughput sequencing (HTS) with a mixture of universal and group-specific primers. The results showed that the biocrusts recruit their microorganisms mainly from the neighboring sand rather than supporting a universal biocrust microbiome. Although in biocrusts the taxa richness was lower than in sand, five times more co-occurrences were identified using network analysis. This study showed that by comparing neighboring bare surface substrates with biocrusts holds the potential to better understand biocrust development. In addition, the target sequencing approach helps outline potential biotic interactions between different microorganisms groups and identify key players during biocrust development.