Biological Soil Crust Communities Research Articles

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.

Reproduction and Dispersal of Biological Soil Crust Organisms

Biological soil crusts (BSCs) consist of a diverse and highly integrated community of organisms that effectively occupy and collectively stabilize soil surfaces. BSCs vary in terms of soil chemistry and texture as well as the environmental parameters that combine to support unique combinations of organisms – including cyanobacteria dominated, lichen-dominated, and bryophyte-dominated crusts. The list of organismal groups that make up BSC communities in various and unique combinations include – free living, lichenized, and mycorrhizal fungi, chemoheterotrophic bacteria, cyanobacteria, diazotrophic bacteria and archaea, eukaryotic algae, and bryophytes. The various BSC organismal groups demonstrate several common characteristics including – desiccation and extreme temperature tolerance, production of various soil binding chemistries, a near exclusive dependency on asexual reproduction, a pattern of aerial dispersal over impressive distances, and a universal vulnerability to a wide range of human-related perturbations. With this publication, we provide literature-based insights as to how each organismal group contributes to the formation and maintenance of the structural and functional attributes of BSCs, how they reproduce, and how they are dispersed. We also emphasize the importance of effective application of molecular and microenvironment sampling and assessment tools in order to provide cogent and essential answers that will allow scientists and land managers to better understand and manage the biodiversity and functional relationships of soil crust communities.

Cultured Microfungal Communities in Biological Soil Crusts and Bare Soils at the Tabernas Desert, Spain

We examined the variations in microfungal communities from different surface types (cyanobacterial crusts, lichen-dominated crusts, and noncrusted bare surface) at two different positions—north-oriented slope and sun-exposed plain in the Tabernas Desert, Spain. A total of 77 species from 46 genera was isolated using the soil dilution plate method. The studied mycobiota, similar to the majority of desert mycobiotas, was dominated by melanin-containing species. However, in the Tabernas crusts, unlike the studied crusts of the Negev Desert (Israel) and the Tengger Desert (China), melanized fungi with large multicellular spores were much less abundantly represented, while the thermotolerant group, Aspergillus spp., remarkably contributed to the communities’ structure. Density of microfungal isolates positively correlated with chlorophyll content indicating possible significant influence of organic matter content on fungal biomass. The variations in crust composition, biomass, and the position of habitats were accompanied by the variations in microfungal community structure, diversity level, and isolate densities, with the communities at the plain sun-exposed position being much less variable than the communities at the north-oriented position. The study shows that microclimatic and edaphic factors play an essential role in the development of crust and noncrust microfungal communities, and their structure can be a sensitive indicator of changing environmental conditions at a microscale.

Habitat-dependent composition of bacterial and fungal communities in biological soil crusts from Oman

Biological soil crusts (biocrusts) occur within drylands throughout the world, covering ~12% of the global terrestrial soil surface. Their occurrence in the deserts of the Arabian Peninsula has rarely been reported and their spatial distribution, diversity, and microbial composition remained largely unexplored. We investigated biocrusts at six different locations in the coastal and central deserts of Oman. The biocrust types were characterized, and the bacterial and fungal community compositions of biocrusts and uncrusted soils were analysed by amplicon sequencing. The results were interpreted based on the environmental parameters of the different sites. Whereas at lowland sites, mainly cyanobacteria-dominated biocrusts were observed, both cyanobacteria- and lichen-dominated biocrusts occurred at mountain sites. The majority of bacterial sequences (32–83% of total sequences) belonged to Actinobacteria, Cyanobacteria, Alphaproteobacteria, and Bacteroidetes, whereas fungal sequences belonged to Ascomycota, Basidiomycota, and Chytridiomycota (>95%). With biocrust development, a notable increase in cyanobacterial and decrease in actinobacterial proportions was observed for cyanobacteria-dominated crusts. In coastal areas, where salinity is high, biocrusts were replaced by a unique marine mat-like microbial community, dominated by halotolerant taxa. Redundancy analysis revealed a significant contribution of soil texture, cover type, carbon content, and elevation to the variations in bacterial and fungal communities. Multivariate analysis placed microbial communities in significantly separated clusters based on their carbon content, elevation and electrical conductivity. We conclude that Oman hosts a variety of cyanobacteria- and lichen-dominated crusts with their bacterial and fungal communities being largely dictated by soil properties and environmental parameters.

Biological soil crust diversity and composition in southwest Idaho, U.S.A.

Biological soil crusts (BSCs) were sampled by habitat types within and adjacent to the Orchard Combat Training Center (OCTC) in southwest Idaho, U.S.A. Plots consisting of a 34.7 m radius circle, approximately equal to one acre or 0.38 hectares were sampled. We focused on five native vascular plant-dominated current habitat types within the OCTC, including: 1) Wyoming sagebrush, 2) saltbush, 3) rabbitbrush, 4) winterfat, and 5) Sandberg bluegrass. We describe how BSC cover and species richness varied with habitat types in the study area. We recorded the relative abundance of BSCs and vascular plant species and collected voucher specimens for each BSC. The biodiversity of each BSC in these arid habitat types was much greater than many ecologists have assumed. We found a total of 68 species of BSC across all 17 plots. BSC cover differed significantly across the different habitat types. BSC cover was significantly higher in sagebrush and saltbush as compared with Poa, rabbitbrush and winterfat habitat types. Overall, there was substantially more BSC richness (17–47 species) than vascular plant richness (4– 13 species), and BSC richness was positively related to vascular plant richness (R2=0.18, p=0.041). On average, each additional plant species was associated with 1.36 additional BSC species. BSC communities also varied across the habitat types with Buellia punctata as a significant indicator species for sagebrush, Toninia sedifolia for saltbush, and Cladonia pocillum for winterfat. Several BSC species were associated with 2 or 3 habitat types; for example, Cladonia fimbriata, Diploschistes muscorum, Leptogium lichenoides, Massalongia carnosa, Riccia sorocarpa and Trapeliopsis steppica were most common in the sagebrush, Poa, and rabbitbrush habitats. In contrast, Caloplaca tominii, Endocarpon loscosii, Placidium squamulosum and Psora tuckermanii were most common in winterfat and saltbush habitats.

Identification of aqueous extracts from Artemisia ordosica and their allelopathic effects on desert soil algae

Desert vascular plants coexist extensively with biological soil crusts (BSCs) in arid lands, but limited information is known about the impacts of shrub litterfall on soil microalgae. In this study, the components of aqueous extracts (AEs) from Artemisia ordosica leaves were identified, and the growth and physiological responses of two BSC-dominated algae, namely, Chlorella vulgaris and Nostoc sp., to AEs were investigated. The AEs contained humic and fulvic acid-like fluorescence components with high aromaticity. They also comprised four main chemical components, namely alcohols, phenols, organic acids and saccharides. Low AE concentrations enhanced the growth rate and chlorophyll fluorescence yield of C. vulgaris. Conversely, high AE concentrations inhibited the growth and photosynthetic activities of both soil microalgae, resulting from the decrease of superoxide dismutase and catalase activities and the accumulation of reactive oxygen species and malondialdehyde contents. The tolerance concentration of the green alga C. vulgaris to the AEs was greater than that of the cyanobacterium Nostoc sp. The AEs from A. ordosica exerted different degrees of stimulatory or inhibitory effects on the growth rates and physiological activities of Nostoc sp. and C. vulgaris, which might affect soil microalgal community structure and BSC formation in drylands. This study reveals the response mechanisms of soil algae to shrub leachates and improves our understanding of the role of vascular plants in shaping BSC communities.

Aerobiology and passive restoration of biological soil crusts

Biological soil crusts (BSCs) exist commonly on soil surfaces in many arid and semiarid areas, and disturbed soil surfaces in more mesic environments. BSCs perform many essential ecological functions. Substantial resources have been invested trying to restore or replace BSCs that have been damaged by anthropogenic disturbances, with various levels of success. The nexus of sciences related to BSC establishment and restoration, and to aerobiology suggests that crusts are established and re-established naturally via commonly occurring ecological processes. Formation of BSCs can be accelerated by implementing traditional or novel land rehabilitation techniques that create near-surface turbulence that facilitates the deposition of airborne BSC organisms. Sexual and asexual propagules of BSC organisms are found naturally in the atmosphere and are transported up to very long distances between continents and hemispheres. Whether restoration of BSCs occurs naturally in this fashion, or through efforts to produce and disseminate artificial inoculants, success is ultimately moderated and governed by the timing and frequency of adequate precipitation relative to the arrival of viable propagules on suitable substrates at appropriate times of year. For the greatest ecological and economic benefit, we suggest that efforts should focus on minimizing the scope and scale of unnecessary anthropogenic disturbance to BSC communities.

Changes in functional gene structure and metabolic potential of the microbial community in biological soil crusts along a revegetation chronosequence in the Tengger Desert

Biological soil crusts (BSCs), the pioneers of restoration of degraded vegetation, act as an organizing principle in drylands largely through metabolic activities of microbial communities. However, little is known about the microbial functional potential involved in biogeochemical processes during BSC succession in desert ecosystems. Here, we utilized a functional gene array (GeoChip 5.0) in conjunction with determinants of microbial community compositions of BSCs along a revegetation chronosequence in the Tengger Desert, to address the following: (a) how the functional structure of the microbial community changes with BSC age in different soils and (b) how genes involved in carbon (C)- and nitrogen (N)-cycling change and whether they promoted an increased microbial metabolic potential during BSC succession in desert revegetation. The results showed that the relative abundance of functional genes was determined by the microbial community compositions in the BSC development process, and the significant differences in microbial functional genes were detected in 61-year-old BSCs from other aged BSCs. Redundancy analysis indicated that the abundance of fungi and moss and soil physicochemical properties were the important factors determining differences in microbial functional structures. Functional genes associated with C degradation and N denitrification were the major components involved in C and N cycles, which were closely related to the increased fungal abundance during succession. The increased gene abundance of 61-year-old BSCs in both C and N cycles promoted microbial metabolic potential. These results indicated that fungi might be the key microbial mediators in C and N cycling in the later development of BSCs, and microbial functional structure could be a potential indicator of revegetation sustainability in desert ecosystems.

Precipitation and soil particle size co-determine spatial distribution of biological soil crusts in the Gurbantunggut Desert, China

Biological soil crusts (BSCs) are bio-sedimentary associations that play crucial ecological roles in arid and semi-arid regions. In the Gurbantunggut Desert of China, more than 27% of the land surface is characterized by a predominant cover of lichen-dominated BSCs that contribute to the stability of the desert. However, little is known about the major factors that limit the spatial distribution of BSCs at a macro scale. In this study, the cover of BSCs was investigated along a precipitation gradient from the margins to the center of the Gurbantunggut Desert. Environmental variables including precipitation, soil particle size, soil pH, electrical conductivity, soil organic carbon, total salt, total nitrogen, total phosphorus and total potassium were analyzed at a macro scale to determine their association with differing assemblages of BSCs (cyanobacteria crusts, lichen crusts and moss crusts) using constrained linear ordination redundancy analysis (RDA). A model of BSCs distribution correlated with environmental variables that dominated the first two axes of the RDA was constructed to clearly demonstrate the succession stages of BSCs. The study determined that soil particle size (represented by coarse sand content) and precipitation are the most significant drivers influencing the spatial distribution of BSCs at a macro scale in the Gurbantunggut Desert. The cover of lichen and moss crusts increased with increasing precipitation, while the cover of cyanobacteria crusts decreased with increasing precipitation. The cover of lichen and moss crusts was negatively associated with coarse sand content, whereas the cover of cyanobacteria crusts was positively correlated with coarse sand content. These findings highlight the need for both the availability of soil moisture and a relatively stable of soil matrix, not only for the growth of BSCs but more importantly, for the regeneration and rehabilitation of disturbed BSC communities in arid and semi-arid lands. Thereby, this study will provide a theory basis to effectively increase soil stability in desert regions.

Biotic soil crust community composition 12–16 years after wildfires in Idaho, U.S.A.

Biological Soil Crusts (BSCs) are important components of sagebrush steppe ecosystems that may be affected by wildfire frequency and severity. As wildfires become more frequent and severe with exotic annual grasses and climate change, it is unknown how BSCs will be affected. We examined the sites of four 12–16 year-old wildfires in Idaho, U.S.A. and adjacent unburned habitats. We found that several lichen and bryophyte species were more frequent and abundant in unburned plots but no species were significantly associated with burned plots. Burned BSC communities were largely a subset of unburned communities. We compared sampling methods using eight 1 m × 1 m subplots per plot to eight 0.25 m × 0.25 m microplots per plot. We observed 80 total taxa in the subplots, as compared with 68 in the microplots. However, even using the smaller sampling area, the difference in community composition between burned and unburned plots was evident. The number of observed taxa was unusually high for BSC studies in the area and may reflect our sampling in varied plant communities in four wildfire sites, unusually well-developed BSCs, larger plot sizes, or greater attention to taxonomic detail. These results add to our understanding of longer-term BSC community recovery following wildfires in the western United States.

Changes in winter snow depth affects photosynthesis and physiological characteristics of biological soil crusts in the Tengger Desert

Water availability is a major limiting factor in desert ecosystems. However, a winter snowfall role in the growth of biological soil crusts is still less investigated. Here, four snow treatments were designed to evaluate the effects of snow depth on photosynthesis and physiological characteristics of biological soil crusts. Results showed that snow strongly affected the chlorophyll fluorescence properties. The increased snow depth led to increased contents of photosynthetic pigments and soluble proteins. However, all biological soil crusts also exhibited a decline in malondialdehyde and soluble sugar contents as snow increased. Results demonstrated that different biological soil crusts exhibited different responses to snow depth treatment due to differences in their morphological characteristics and microhabitat. In addition, interspecies differentiation in response to snow depth treatment might affect the survival of some biological soil crusts. Further, this influence might lead to changes in the structural composition and functional communities of biological soil crusts.

Marked Succession of Cyanobacterial Communities Following Glacier Retreat in the High Arctic.

Cyanobacteria are important colonizers of recently deglaciated proglacial soil but an in-depth investigation of cyanobacterial succession following glacier retreat has not yet been carried out. Here, we report on the successional trajectories of cyanobacterial communities in biological soil crusts (BSCs) along a 100-year deglaciation gradient in three glacier forefields in central Svalbard, High Arctic. Distance from the glacier terminus was used as a proxy for soil age (years since deglaciation), and cyanobacterial abundance and community composition were evaluated by epifluorescence microscopy and pyrosequencing of partial 16S rRNA gene sequences, respectively. Succession was characterized by a decrease in phylotype richness and a marked shift in community structure, resulting in a clear separation between early (10-20years since deglaciation), mid (30-50years), and late (80-100years) communities. Changes in cyanobacterial community structure were mainly connectedwith soil age and associated shifts in soil chemical composition (mainly moisture, SOC, SMN, K, and Na concentrations). Phylotypes associated with early communities were related either to potentially novel lineages (< 97.5% similar to sequences currently available in GenBank) or lineages predominantly restricted to polar and alpine biotopes, suggesting that the initial colonization of proglacial soil is accomplished by cyanobacteria transported from nearby glacial environments. Late communities, on the other hand, included more widely distributed genotypes, which appear to establish only after the microenvironment has been modified by the pioneering taxa.

Multiple, Distinct Intercontinental Lineages but Isolation of Australian Populations in a Cosmopolitan Lichen-Forming Fungal Taxon, Psora decipiens (Psoraceae, Ascomycota).

Multiple drivers shape the spatial distribution of species, including dispersal capacity, niche incumbency, climate variability, orographic barriers, and plate tectonics. However, biogeographic patterns of fungi commonly do not fit conventional expectations based on studies of animals and plants. Fungi, in general, are known to occur across exceedingly broad, intercontinental distributions, including some important components of biological soil crust communities (BSCs). However, molecular data often reveal unexpected biogeographic patterns in lichenized fungal species that are assumed to have cosmopolitan distributions. The lichen-forming fungal species Psora decipiens is found on all continents, except Antarctica and occurs in BSCs across diverse habitats, ranging from hot, arid deserts to alpine habitats. In order to better understand factors that shape population structure in cosmopolitan lichen-forming fungal species, we investigated biogeographic patterns in the cosmopolitan taxon P. decipiens, along with the closely related taxa P. crenata and P. saviczii. We generated a multi-locus sequence dataset based on a worldwide sampling of these taxa in order to reconstruct evolutionary relationships and explore phylogeographic patterns. Both P. crenata and P. decipiens were not recovered as monophyletic; and P. saviczii specimens were recovered as a monophyletic clade closely related to a number of lineages comprised of specimens representing P. decipiens. Striking phylogeographic patterns were observed for P. crenata, with populations from distinct geographic regions belonging to well-separated, monophyletic lineages. South African populations of P. crenata were further divided into well-supported sub-clades. While well-supported phylogenetic substructure was also observed for the nominal taxon P. decipiens, nearly all lineages were comprised of specimens collected from intercontinental populations. However, all Australian specimens representing P. decipiens were recovered within a single well-supported monophyletic clade consisting solely of Australian samples. Our study supports up to 10 candidate species-level lineages in P. decipiens, based on genealogical concordance and coalescent-based species delimitation analyses. Our results support the general pattern of the biogeographic isolation of lichen-forming fungal populations in Australia, even in cases where closely related congeners have documented intercontinental distributions. Our study has important implications for understanding factors influencing diversification and distributions of lichens associated with BSC.

Biological crusts of serpentine and non‐serpentine soils from the Barberton Greenstone Belt of South Africa

AbstractClimate and geography can influence biological soil crust (BSC) community composition, but local heterogeneity in variables such as soil characteristics or microclimate gradients can also impact cryptogamic diversity. Heavy metals and nutrient imbalances in serpentine soils are known to influence the distributions of higher plants, but cryptogamic species appear to be more tolerant of substrate. The aim of this study was to compare the cryptogamic composition of serpentine and non‐serpentine soils by using integrative taxonomy, which combines morphological and DNA barcoding data, to determine how soil characteristics in combination with rainfall can influence BSC community composition. Samples from serpentine and non‐serpentine soils were enumerated and total genomic DNA was isolated from the soil samples. Analyses of the 16S rRNA gene and ITS sequences were done using the quantitative insights into microbial ecology (QIIME) workflow to determine which eukaryotic microorganisms were present in the samples. Sixty genera from the Cyanophyceae (38), Chlorophyceae (10), Bacillariophyceae (6), Eustigmatophyceae (4), Trebouxiophyceae (1) and Xanthophyceae (1) classes were detected with this approach. Results confirm that algae and cyanobacteria are tolerant of most substrates and can even colonize environments with high levels of heavy metal and nutrient imbalances, if moisture is present. Genera such as Acaryochloris, Annamia, Brasilonema, Chrocosphaera, Halomicronema, Planktothricoides, Rubidibacter, and Toxopsis are reported for the first time for South African soil.

Resolving neutral and deterministic contributions to genomic structure in Syntrichia ruralis (Bryophyta, Pottiaceae) informs propagule sourcing for dryland restoration

Syntrichia ruralis is a cosmopolitan moss that occupies steep environmental gradients. In arid to semi-arid regions of the world it is a key component of biological soil crusts, which are fundamental to healthy dryland ecosystem processes. As such, S. ruralis has attracted the attention of conservationists seeking to restore degraded biological soil crust communities and their associated vascular flora. Here, we generate genomic data for S. ruralis populations that span climatic gradients across the Colorado Plateau of the southwestern USA to investigate the contributions of neutral and deterministic processes to the partitioning of genomic structure. Although S. ruralis appears to be highly dispersible, geographic proximity significantly predicts genomic similarity. In addition, even when taking into account apparently high migration rates among populations and spatial autocorrelation of allele frequencies, some genomic variation is explained by environmental gradients correlated with elevation and latitude. Consequently, efforts to restore dryland ecosystems by establishing S. ruralis as a foundation should include strategies to ensure that propagule sources of this moss are environmentally stratified and targeted to the current/future climates of restoration sites.

Recovery of biological soil crust richness and cover 12–16 years after wildfires in Idaho, USA

Abstract. Changing fire regimes in western North America may impact biological soil crust (BSC) communities that influence many ecosystem functions, such as soil stability and C and N cycling. However, longer-term effects of wildfire on BSC abundance, species richness, functional groups, and ecosystem functions after wildfire (i.e., BSC resilience) are still poorly understood. We sampled BSC lichen and bryophyte communities at four sites in Idaho, USA, within foothill steppe communities that included wildfires from 12 to 16 years old. We established six plots outside each burn perimeter and compared them with six plots of varying severity within each fire perimeter at each site. BSC cover was most strongly negatively impacted by wildfire at sites that had well-developed BSC communities in adjacent unburned plots. BSC species richness was estimated to be 65 % greater in unburned plots compared with burned plots, and fire effects did not vary among sites. In contrast, there was no evidence that vascular plant functional groups or fire severity (as measured by satellite metrics differenced normalized burn ratio (dNBR) or relativized differenced normalized burn ratio (RdNBR)) significantly affected longer-term BSC responses. Three large-statured BSC functional groups that may be important in controlling wind and water erosion (squamulose lichens, vagrant lichens, and tall turf mosses) exhibited a significant decrease in abundance in burned areas relative to adjacent unburned areas. The decreases in BSC cover and richness along with decreased abundance of several functional groups suggest that wildfire can negatively impact ecosystem function in these semiarid ecosystems for at least 1 to 2 decades. This is a concern given that increased fire frequency is predicted for the region due to exotic grass invasion and climate change.

Development of bacterial communities in biological soil crusts along a revegetation chronosequence in the Tengger Desert, northwest China

Abstract. Knowledge of structure and function of microbial communities in different successional stages of biological soil crusts (BSCs) is still scarce for desert areas. In this study, Illumina MiSeq sequencing was used to assess the compositional changes of bacterial communities in different ages of BSCs in the revegetation of Shapotou in the Tengger Desert. The most dominant phyla of bacterial communities shifted with the changed types of BSCs in the successional stages, from Firmicutes in mobile sand and physical crusts to Actinobacteria and Proteobacteria in BSCs, and the most dominant genera shifted from Bacillus, Enterococcus and Lactococcus to RB41_norank and JG34-KF-361_norank. Alpha diversity and quantitative real-time polymerase chain reaction (PCR) analysis indicated that bacterial richness and abundance reached their highest levels after 15 years of BSC development. Redundancy analysis showed that silt + clay content and total K were the prime determinants of the bacterial communities of BSCs. The results suggested that bacterial communities of BSCs recovered quickly with the improved soil physicochemical properties in the early stages of BSC succession. Changes in the bacterial community structure may be an important indicator in the biogeochemical cycling and nutrient storage in early successional stages of BSCs in desert ecosystems.

Metabolic activity duration can be effectively predicted from macroclimatic data for biological soil crust habitats across Europe

Biological soil crusts (BSC) perform several important environmental functions such as soil erosion prevention, soil nutrient enrichment through photosynthesis and nitrogen fixation, and are receiving growing interest due to their importance in some changing habitats with soils under degradation risk. Primary producers within BSC (cyanobacteria, lichens, algae and bryophytes) are all poikilohydric and active only when wet, meaning that knowledge of the period of metabolic activity is essential to understand growth and adaptation to environment. Finding links with macroclimatic factors would allow not only prediction of activity but also the effects of any climate change over these communities. Metabolic activity and microclimate of BSC at four sites across Europe with different soils from semi-arid (Almeria, SE Spain) to alpine (Austria) was monitored during one year using a chlorophyll fluorometer. Local climatic data were also recorded. Mean monthly activity of crust within each site were strongly linked irrespective of crust type whilst, using the data from all sites, highly significant linear relationships (mean monthly values) were found for activity with incident light, air temperature and air relative humidity, and a nonlinear response to rainfall saturating at about 40mm per month. Air relative humidity and air temperature were the best predictors of metabolic activity duration. The links observed are all highly significant allowing climate data to be used to model activity and to gain inferences about the effects of climate change over BSC communities, soil structure and fertility. Linear relationships mean that small changes in the environment will not produce massive alterations in activity. BSC also appear to behave as a single functional group, which is helpful when proposing general management policies for soil ecosystems protection.

Differential effects of the crustose Diploschistes diacapsis and the squamulose Fulgensia bracteata on the establishment of a Mediterranean grass species

AbstractThe interest of the scientific community in biological soil crusts has grown exponentially over the last decades. One of the scientific research interests is the study of the effect of these crusts on plant establishment. Findings in this topic have been controversial, and some differences were attributed to crust types. Biological soil crusts dominated by lichens are common components of Stipa tenacissima steppes in arid and semi‐arid environments of the southern Mediterranean. In the current study, we conducted growth chamber experiments to investigate the differential effects of two lichen species with continuous crustose thalli (Diploschistes diacapsis) and with squamulose semicontinuous thalli (Fulgensia bracteata) on seed germination, root penetration, shoot emergence and seed viability of the tussock grass species S. tenacissima. Our results showed that under laboratory conditions, two distinct lichen species had significantly different effects on the establishment of S. tenacissima. Our findings clearly demonstrated that D. diacapsis significantly decreased germination, root penetration and shoot emergence of S. tenacissima compared to F. bracteata. This can be related to differences in morphological and physiological characteristics between crustose and squamulose lichens. Overall, we suggest that D. diacapsis and crustose lichens generally can act as natural barrier to the establishment of S. tenacissima.

Nitrogenase activity by biological soil crusts in cold sagebrush steppe ecosystems

In drylands worldwide, biological soil crusts (BSC) form a thin photosynthetic cover across landscapes, and provide vital benefits in terms of stabilizing soil and fixing nitrogen (N) and carbon (C). Numerous studies have examined the effects of climate and disturbance on BSC functions; however, few have characterized these responses in rolling BSCs typical of northern ecosystems in the Intermountain West, US. With temperature increases and shifts in precipitation projected, it is unclear how BSCs in this region will respond to climate change, and how the response could affect their capacity to perform key ecosystem functions, such as providing ‘new’ N through biological N2 fixation. To address this important knowledge gap, we examined nitrogenase activity (NA) associated with rolling BSCs along a climatic gradient in southwestern Idaho, US, and quantified how acetylene reduction rates changed as a function of climate, grazing (using exclosures), and shrub-canopy association. Results show that warmer, drier climates at lower elevations hosted greater cover of late successional BSC communities (e.g., mosses and lichens), and higher NA compared with colder, wetter climates at higher elevations. Highest NA (0.5–29.3 µmol C2H4 m−2 h−1) occurred during the early summer/spring, when water was more available than in late summer/autumn. Activity was strongly associated with soil characteristics including pH and ammonium concentrations suggesting these characteristics as potentially strong controls on NA in BSCs. The relationship between grazing and NA varied with elevation. Specifically, lower elevation sites had lower NA at grazed locations, whereas higher elevation sites had higher NA with grazing. At both low and high ends of the elevation gradient, shrub-canopy associated BSCs maintained two to three times higher NA compared to BSCs in the interspace among shrubs. Taken together, our findings indicate that the controls and rates of NA in BSCs vary seasonally and strongly with climate in the Intermountain West, and that drier springs are likely to influence rates of NA more than warmer summers.