Diversity Of Biological Soil Crusts Research Articles

Soil type and precipitation level have a greater influence on fungal than bacterial diversity in serpentine and non‐serpentine biological soil crusts

AbstractSerpentine soils are characterized by nutrient imbalances and high levels of potentially toxic metals (PTMs). These soils host depauperate plant communities of species with specialized adaptations. Initial studies showed that South African serpentine soils harbor distinct biocrust algal and cyanobacterial species compared to adjacent non‐serpentine soils, with these communities further differing based on high and low precipitation levels. Here, we investigated the bacterial and fungal diversity of biological soil crusts from serpentine and non‐serpentine soils at two precipitation levels. The bacterial and fungal communities were characterized using 16S rDNA and ITS metabarcoding, respectively. No significant differences could be found in bacterial richness and community structure. Nevertheless, bacterial taxa such as Archangium, Candidatus Solibacter, Chthoniobacter, and Microvirga were more abundant in serpentine biocrusts or biocrusts receiving lower precipitation. The fungal community structure was distinct between serpentine and non‐serpentine soils (p = 0.027) and between high and low precipitation (p = 0.018). Furthermore, fungal diversity was lowest in the drier, serpentine biocrusts compared to non‐serpentine (p = 0.001) and serpentine crusts receiving higher precipitation (p = 0.002). The fungal genera, Ramimonilia and Vishniacozyma, which are known to be resistant or tolerant to PTMs and other environmental extremes, were significantly more abundant (p = 0.036 and p = 0.016, respectively) in serpentine biocrusts, with the latter indicating serpentine habitats. This study concluded that soil type influenced the fungal alpha diversity, specifically in the serpentine soil, resulting in a decrease in fungal species richness. Furthermore, precipitation influenced fungal beta diversity by shaping distinct fungal communities found in the biocrusts of serpentine and non‐serpentine soils.

Cyanobacterial diversity of biological soil crusts and soil properties in karst desertification area.

As important components of the biological soil crusts (BSCs) and of the primary stage of crust succession, cyanobacterial communities occupy an important ecological niche and play an important ecological role in desertification areas. In this study, we focused on the karst desertification area, which also belongs to the same category of desertification, and selected three study areas, Guanling-Zhenfeng Huajiang (HJ), Bijie Salaxi (SLX), and Shibing (SB), in the Guizhou Plateau, which represents the overall ecological environment of South China karst, to conduct surveys on the diversity of BSC species and soil properties. Analysis of the cyanobacterial communities and physicochemical properties using the Shannon-Wiener diversity index, principal component analysis, and redundancy analysis revealed that: (1) The three study areas had common cyanobacterial species, with a total of 200 species distributed across 22 genera, 2 classes, 5 orders, and 6 families belonging to the Oscillatoriales (39%), Scytonematales (24.5%), Chroococcales (23%), Nostocales (11.5%), and Rivulariales (2%), (2) The number of species increased with the intensity of karst desertification-while Oscillatoriaceae was the dominant family in HJ and moderate-severe desertification areas, Chroococcaceae and Scytonemataceae were dominant in the mild and potential desertification areas SLX and SB, (3) The Shannon-Wiener diversity indices followed the trend: SLX (3.56) > SB (3.08) > HJ (3.01), indicating that the species were more evenly distributed in mild desertification, (4) In the carbonate background, shrubland harbored the largest number of cyanobacterial species compared to grassland, bare land, and arbor woodland; however, the highest number was documented in arbor woodland in dolomite karst, (5) The soil is weathered limestone or yellow soil in all three areas, with pH ranging from 5.73 to 6.85, fine sand dominated, and soil nutrients increased with the intensity of desertification, and (6) Redundancy analysis showed that organic carbon, soil moisture content (0-5 cm), and total nitrogen substantially influenced cyanobacterial diversity. These results reveal that differences in soil nutrient content play an important role in regulating the cyanobacterial diversity and composition, thereby establishing a foundation for further research and application of soil ecological restoration of cyanobacteria in BSCs of karst desertification areas.

Grazing pressure interacts with aridity to determine the development and diversity of biological soil crusts in Patagonian rangelands

AbstractGrazing is directly related to land degradation and desertification in global drylands. Grazing impacts on vascular plants, reasonably well‐known, depend on its intensity and are modulated by local aridity conditions. However, we do not know how the interplay of grazing intensity and aridity affect biocrusts, topsoil assemblages dominated by cyanobacteria, lichens, and mosses that provide key ecosystem services in drylands. Here, we determined how grazing affects biomass, total cover, and richness of biocrust structural types across a regional aridity gradient in the Patagonian steppe. On average, grazing by sheep reduced biocrust biomass, total cover and richness of structural types by 55, 90, and 59%, respectively. In general, high grazing pressures had a larger impact on biocrusts than moderate or light grazing pressures. For example, biocrust cover was reduced by 85, 89, and 98% by light, moderate, and high grazing pressures, respectively. Although a slightly different response to grazing was observed under low aridity conditions, these more benign climatic conditions did not compensate for the negative effects of trampling by domestic animals on biocrusts. Nonetheless, estimated biocrust recovery rates under medium aridity conditions were faster than previously thought: it took 24, 18, and 58 years to double biocrust biomass, total cover, and richness of structural types. Sheep cannot be just removed in Patagonian rangelands because the production of meat and wool represents the main local economic activity. But landowners must consider our results to protect the ecosystem functions and services provided by biocrusts for future generations to come.

Composition of biological soil crusts from sand dunes of the Baltic Sea coast in the context of an integrative approach to the taxonomy of microalgae and cyanobacteria

ABSTRACT Most of the data on biodiversity, ecology and biogeography of microalgae and cyanobacteria are based on classical morphological approaches. However, morphological identification of these microorganisms is often possible only to higher taxonomic ranks such as genus, because of low morphological diversity and high variability along with the presence of cryptic taxa. This study compared the species composition of cyanobacteria, and green and streptophyte microalgae, isolated from biological soil crusts (BSCs) of maritime sand dunes (Baltic Sea, Germany) and identified through culture-dependent morphological methods combined with molecular phylogenetic data. Phylogenetic analyses (based on SSU rRNA and ITS-1,2 for microalgae, or the SSU-LSU ITS region for cyanobacteria) provided unambiguous identifications of 20 strains (37.7% of all strains investigated) to species level; the identifications had to be corrected after preliminary morphological determination of eight strains. For 27 strains (50.9%), identification with molecular markers was possible only to genus or group of closely related species, because a modern taxonomic revision of these taxa is preliminary, incomplete or non-existent. Identification to genus was problematic for six strains (11.3%). This combination of morphological and molecular methods (integrative approach) resulted in the discovery of rare, taxonomically or ecologically interesting taxa, and in the description of a new species of Tetradesmus (T. arenicola sp. nov.), a new combination for Chlamydomonas callunae (Heterochlamydomonas callunae comb. nov.), epitypification of the rare alga Actinochloris sphaerica and emendation of the recently described Eremochloris sphaerica. A microscopic culture-dependent method and an integrative approach provided similar results concerning the cyanobacterial and algal diversity of BSCs of Baltic sand dunes in general. However, this investigation using an integrative approach allowed us to precisely identify species of several important taxa (the most common and dominant species) in the community structure of BSCs, and also certain rare representatives.

Regulation of carbon and nitrogen exchange rates in biological soil crusts by intrinsic and land use factors in the Sahel area

The occurrence and diversity of biological soil crusts (BSC) a thin soil surface layer composed of phototrophic and heterotrophic microorganisms intimately associated with soil particles, are known as strong indicators of ecosystem health and sensitivity to soil surface disturbances and are key factors in the biochemical cycling of carbon and nitrogen in drylands. However, the impact of land use on C and N budgets related to BSC dynamics is poorly understood and hinders the prediction of changes in soil fertility in response to future land use scenarios. In this study, we examined the C and N exchange rates of BSC sampled along a north-south pluviometric gradient of the Sub-Sahel, which provides evidence of increasing human land pressure, leading to a gradient in fallow duration and trampling intensity. We demonstrate that the net and gross photosynthesis by BSC significantly increases with fallow duration and a reduction of trampling intensity, thus affecting BSC fine particles and relative water content. Conversely, no effect of land use was found on N fixation or mineralisation rates, which are instead regulated by the N availability within the crust. Simple statistical models were derived from the relationships between C exchange rates and BSC intrinsic characteristics related to soil surface disturbances. The proposed statistical models were tested for C gas exchange with independent data obtained from a new BSC dataset sampled in Burkina Faso and Niger. A simple equation using BSC fine particle content as a unique variable was found to explain between 60 and 70% of the gross photosynthesis. Our findings will help in mapping photosynthesis and estimating the contribution of BSC to the carbon budget at a regional scale in the dryland area of the Sahel and to further testing of land use change scenarios.

High Bacterial Diversity of Biological Soil Crusts in Water Tracks over Permafrost in the High Arctic Polar Desert

In this study we report the bacterial diversity of biological soil crusts (biocrusts) inhabiting polar desert soils at the northern land limit of the Arctic polar region (83° 05 N). Employing pyrosequencing of bacterial 16S rRNA genes this study demonstrated that these biocrusts harbor diverse bacterial communities, often as diverse as temperate latitude communities. The effect of wetting pulses on the composition of communities was also determined by collecting samples from soils outside and inside of permafrost water tracks, hill slope flow paths that drain permafrost-affected soils. The intermittent flow regime in the water tracks was correlated with altered relative abundance of phylum level taxonomic bins in the bacterial communities, but the alterations varied between individual sampling sites. Bacteria related to the Cyanobacteria and Acidobacteria demonstrated shifts in relative abundance based on their location either inside or outside of the water tracks. Among cyanobacterial sequences, the proportion of sequences belonging to the family Oscillatoriales consistently increased in relative abundance in the samples from inside the water tracks compared to those outside. Acidobacteria showed responses to wetting pulses in the water tracks, increasing in abundance at one site and decreasing at the other two sites. Subdivision 4 acidobacterial sequences tended to follow the trends in the total Acidobacteria relative abundance, suggesting these organisms were largely responsible for the changes observed in the Acidobacteria. Taken together, these data suggest that the bacterial communities of these high latitude polar biocrusts are diverse but do not show a consensus response to intermittent flow in water tracks over high Arctic permafrost.

Warming reduces the growth and diversity of biological soil crusts in a semi-arid environment: implications for ecosystem structure and functioning

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.

Competition increases with abiotic stress and regulates the diversity of biological soil crusts

Summary 1. The stress‐gradient hypothesis (SGH) predicts that the frequency of facilitative and competitive interactions will vary inversely across abiotic stress gradients, with facilitation being more common when abiotic stress is high. The effect of competition intensity on species richness is generally thought to be negative, but tests along true stress gradients are lacking. This body of research has primarily focused on vascular plants and could be well informed by broadening to other communities. 2. We report the first regional‐scale test of the SGH using biological soil crusts dominated by mosses and lichens, a key multi‐functional community of arid and semi‐arid ecosystems worldwide. We examined the intensity of facilitative or competitive interactions at the level of the community and among species pairs along an aridity gradient. Along this gradient we also examined the relationship between competition intensity and species richness. 3. All evidence strongly suggested that negative species interactions are prevalent in this study system and much more common than expected by chance. At the community scale, we found that abiotic stress associated with aridity was positively related to and explained 6–56% of the variance in indicators of facilitation or competition, dependent on the index and algorithm used. Despite this intriguing contradiction of the SGH at the whole community scale, we found scant dependency of species‐level interactions upon abiotic stress. However, the sign and intensity of these interactions proved to be species‐specific. We also found that the relationship between competition and species richness, usually negatively affected by competition, was positively related to richness at low abiotic stress, and negatively related to richness at high abiotic stress. 4. Synthesis. We propose that the response of species interactions to stress gradients may partially depend upon the particular modes of facilitation and competition, in addition to type of stressor and life‐history strategies of species involved. We also hypothesize that because stress can act as a filter, a greater number of species interactions are possible under low stress conditions. We believe that this may render intransitivity dominant over niche segregation and expansion, potentially resulting in positive effects of competition on species richness in low stress situations.

The Community and Phylogenetic Diversity of Biological Soil Crusts in the Colorado Plateau Studied by Molecular Fingerprinting and Intensive Cultivation

We studied the bacterial communities in biological soil crusts (BSCs) from the Colorado Plateau by enrichment and cultivation, and by statistically analyzed denaturing gradient gel electrophoresis (DGGE) fingerprinting of environmental 16S rRNA genes, and phylogenetic analyses. Three 500-m-long transects, tens of km apart, consisting of 10 equally spaced samples each, were analyzed. BSC communities consistently displayed less richness (10-32 detectable DGGE bands per sample) and Shannon diversity (2.1-3.3) than typical soil communities, with apparent dominance by few members. In spite of some degree of small-scale patchiness, significant differences in diversity and community structure among transects was detectable, probably related to the degree of crust successional maturity. Phylogenetic surveys indicated that the cyanobacterium Microcoleus vaginatus was dominant, with M. steenstrupii second among phototrophs. Among the 48 genera of nonphototrophs detected, Actinobacteria (particularly Streptomyces spp.) were very common and diverse, with 18 genera and an average contribution to the total 16S rDNA amplificate of 11.8%. beta-Proteobacteria and Bacteriodetes contributed around 10% each; Low-GC Gram-positives, alpha-Proteobacteria, Thermomicrobiales, and Acidobacteria were common (2-5%). However, the second largest contribution was made by deep-branching unaffiliated alleles (12.6%), with some of them representing candidate bacterial divisions. Many of the novel strains isolated are likely new taxa, and some were representatives of the phylotypes detected in the field. The mucoid or filamentous nature of many of these isolates speaks for their role in crust formation.