Biological Soil Crusts Research Articles

Biological soil crusts determine soil properties and salt dynamics under arid climatic condition in Qara Qir, Iran

Biological soil crusts are a thin layer within the soil system but strongly determine the infiltration, runoff and water and solute movement. Little is known about the role of biological soil crusts on soil solute dynamics in arid ecosystems and the objective of this paper is to determine in Qara Qir rangeland how biological soil crusts control the water and salt distribution along the soil profile. Rainfall simulation experiments were carried out at five locations, and measurements of the soil at 0–5, 5–10, 10–20, 20–30, 30–50 and 50–80 cm depth were done before, 48 h and 21 days after the rainfall simulations. Soil particle size distribution, bulk density, water content, organic carbon and electrical conductivity were measured at each of the 270 samples (3 seasons × 3 times × 5 sites × 6 depths). Biological soil crusts increased soil organic carbon, soil water content, and infiltration rate; and biological soil crusts decreased soil bulk density, clay fraction, electrical conductivity, and other saline-sodic properties, especially in the upper layers (0–10 cm). Large pores in soils covered by biological soil crusts enhanced the preferential flows, infiltration and solute transport. Biological soil crusts not only directly affected the soil surface, but also influenced soil properties, and consequently determined spatio-temporal soil salinity distribution. Biological soil crusts act as a soil salinity reducing agent and contribute to the soil quality improvement under arid climatic conditions. Biological soil crusts can be considered as a soil conservation strategy and actively used in soil rehabilitation and ecosystems restoration.

Biological soil crust (BSC) is an effective biofertilizer on Vigna mungo (L.).

Biological soil crusts (BSC) (Cyanobacteria) play an important role in the soil nitrogen fixation and soil stabilization. However, limited researches were carried out about the diversity and distribution of Bio crust in sacred forests. The study aims to identify the distribution of cyanobacteria in biological soil crusts from different sacred groves of Ariyalur and Pudukottai, Tamil Nadu. We identified following microbes of Microcoleus, Scytonema, Anabaena and Nostoc in biological soil crust. A surface experiment was conducted for the efficacy of biological soil crusts on crops seedling growths. The efficacy was assessed by measuring the root & shoot length, dry & fresh weight of the plant, total chlorophyll, protein & carbohydrate content, with reducing sugar. The plant growth was higher in biocrust inoculated pot than the control. In corresponding nitrogenase activity was determined by the acetylene reduction assay, and phytohormones documentation was executed by the high-performance liquid chromatography. The results indicating that the biological soil crusts are the promising factors influencing the plant growth by plant growth-stimulating auxins and nitrogenase activity.

Stabilizing sand from dried-up lakebeds against wind erosion by accelerating biological soil crust development

Land degradation and the resulting desertification often lead to sand flowing from deserts and/or dried-up lakebeds and into habitable zones; a problem that has intensified in recent decades. We cultivated locally collected biological soil crust (BSC) bacteria (Bacillus subtilis strain) and cyanobacteria (Nostoc sp. and Oscillatoria sp.) from the dried-up bed of Lake Urmia, northwest Iran. To evaluate the ability of BSC to stabilize the sandy lakebed soil, bacteria and cyanobacteria were used to inoculate experimental trays of sandy soil from the same area, under laboratory conditions. After 120 days, we simulated winds at a speed of 72 km h−1 for three 10-min intervals (30 min in overall) to measure the sand transport rate as well as the durability and fragility of the BSCs during the wind erosion process, using an open circuit wind tunnel. We found that the bacteria, cyanobacteria, and cyanobacteria + bacteria inoculation reduced the sand flowing by 42.3, 96.6, and 95.9%, respectively, as compared to the control. We found that in addition to creating a protective cover on the soil surface, cyanobacteria created a strong bond between the soil particles through their exudation of exopolysaccharides and network of filaments, increasing the ability of the sand to withstand wind forces. Our inoculation technique was an effective and natural way to stabilize moving sand. Future research should replicate our methods under natural conditions to evaluate the potential for large-scale restoration.

Biological Soil Crusts as Modern Analogs for the Archean Continental Biosphere: Insights from Carbon and Nitrogen Isotopes.

Stable isotope signatures of elements related to life such as carbon and nitrogen can be powerful biomarkers that provide key information on the biological origin of organic remains and their paleoenvironments. Marked advances have been achieved in the last decade in our understanding of the coupled evolution of biological carbon and nitrogen cycling and the chemical evolution of the early Earth thanks, in part, to isotopic signatures preserved in fossilized microbial mats and organic matter of marine origin. However, the geologic record of the early continental biosphere, as well as its evolution and biosignatures, is still poorly constrained. Following a recent report of direct fossil evidence of life on land at 3.22 Ga, we compare here the carbon and nitrogen isotopic signals of this continental Archean biosphere with biosignatures of cyanobacteria biological soil crusts (cyanoBSCs) colonizing modern arid environments. We report the first extended δ13C and δ15N data set from modern cyanoBSCs and show that these modern communities harbor specific isotopic biosignatures that compare well with continental Archean organic remains. We therefore suggest that cyanoBSCs are likely relevant analogs for the earliest continental ecosystems. As such, they can provide key information on the timing, extent, and possibly mechanism of colonization of the early Earth's emergent landmasses.

Spectral Response Assessment of Moss-Dominated Biological Soil Crust Coverage Under Dry and Wet Conditions

Biological soil crusts (BSCs) are a major functional vegetation unit, covering extensive parts of drylands worldwide. Therefore, several multispectral indices have been proposed to map the spatial distribution and coverage of BSCs. BSCs are composed of poikilohydric organisms, the activity of which is sensitive to water availability. However, studies on dry and wet BSCs have seldom considered the mixed coverage gradient that is representative of actual field conditions. In this study, in situ spectral data and photographs of 136 pairs of dry and wet plots were collected to determine the influence of moisture conditions on BSC coverage detection. Then, BSC spectral reflectance and continuum removal (CR) reflectance responses to wetting were analyzed. Finally, the responses of four commonly used indices (i.e., normalized difference vegetation index (NDVI); crust index (CI); biological soil crust index (BSCI); and band depth of absorption feature after CR in the red band, (BD_red)), calculated from in situ hyperspectral data resampled to two multispectral data channels (Landsat-8 and Sentinel-2), were compared in dry and wet conditions. The results indicate that: (i) on average, the estimated BSC coverage using red-green-blue (RGB) images is 14.98% higher in wet than in dry conditions (P < 0.001); (ii) CR reflectance features of wet BSCs are more obvious than those of dry BSCs in both red and red-edge bands; and (iii) NDVI, CI, and BSCI for BSC coverage of 0%–60% under dry and wet conditions are close to those of dry and wet bare sand, respectively. NDVI and BD_red cannot separate dead wood and BSC with low coverage. This study demonstrates that low-coverage moss-dominated BSC is not easily detected by the four indices. In the future, remote-sensing data obtained during the rainy season with red and red-edge bands should be considered to detect BSCs.

Multifunctionality of biocrusts is positively predicted by network topologies consistent with interspecies facilitation.

The potential of biodiversity loss to impair the delivery of ecosystem services has motived ecologists to better understand the relationship between biodiversity and ecosystem functioning. Although increasing evidence underlines the collective contribution of different biodiversity components on the simultaneous performance of multiple functions (multifunctionality), we know little about the trade‐offs between individual diversity effects and the extent to which they determine multifunctionality differentially. Here, at a subcontinental scale of 62 dryland sites, we show in phototrophic microbiota of biological soil crusts (biocrusts) that, whereas richness alone is unable to guarantee the maxima of multifunctional performance, interspecies facilitation and compositional identity are particularly stronger but often neglected predictors. The inconsistent effects of different biodiversity components imply that soil multifunctionality can be lost despite certain species remaining present. Moreover, we reveal a significant empirical association between species functional importance and its topological feature in co‐occurrence networks, indicating a functional signal of species interaction. Nevertheless, abundant species tend to isolate and merely interact within small topological structures, but rare species were tightly connected in complicated network modules. Our findings suggest that abundant and rare species of soil phototrophs exhibit distinct functional relevance. These results give a comprehensive view of how soil constructive species drive multifunctionality in biocrusts and ultimately promote a deeper understanding of the consequences of biodiversity loss in real‐world ecosystems.

Practices of biological soil crust rehabilitation in China: experiences and challenges

Biological soil crusts (biocrusts) are a central component of dryland ecosystems. However, they are highly vulnerable to disturbance and natural recovery may be slow. Therefore, finding ways to enhance the reestablishment of biocrusts after disturbance has been of great interest to researchers. This article provides a review of the laboratory cultivation and field inoculations of biocrust materials in China (mostly published in Chinese). Larger filamentous cyanobacteria (e.g.Microcoleus) are relatively easy, although slow, to grow in culture compared to other biocrust components. Thus, most researchers have focused their efforts on the cyanobacteria and a few species of mosses that are also easily grown but at smaller scale. For all the studies, a small amount of biocrust material was collected and its biomass enhanced under controlled conditions. However, the enhancement was done using various methods and techniques in different regions. These materials were then applied to disturbed field sites, again with various methods. Results show that keeping the inoculated soil surface wet for some time period after inoculation was crucial for restoration success. Cyanobacterial establishment was improved by installing automatic sprinkling using micro‐irrigation techniques and/or physical structures that reduced sediment moving onto the inoculated area. Experimental applications in China showed that cyanobacteria can be successfully inoculated at a large scale (hundreds of ha). Moss inoculation, on the other hand, was only accomplished at a small scale (several m2). To assess whether biocrust restoration can enhance the establishment of a self‐supporting ecosystem, further research is needed on how inoculation affects vegetation diversity and structure and ecological processes.

Multiple mechanisms determine the effect of warming on plant litter decomposition in a dryland

In drylands, where soil fertility is typically low, plant litter decomposition provides particularly critical carbon and nitrogen inputs into soil. Although climate change is projected to increase the already large global extent of drylands, it is unknown how warmer temperatures will affect core ecosystem processes, such as plant litter decomposition, in these systems. To address this key unknown, we conducted a litterbag study in a long-term dryland warming experiment in southeastern Utah, USA. Unexpectedly, we did not find an overall effect of warming on leaf litter mass loss over time. Instead, our results indicated both positive and negative effects of warming on mass loss which offset one another. In particular, our findings suggested that a warming-induced degradation of biological soil crusts (soil surface community of mosses, lichens, and/or cyanobacteria that live in drylands worldwide) increased soil-litter mixing, thereby accelerating decomposition. Results also suggested that a warming-induced reduction in litter moisture slowed decomposition. In addition, we found that warming lowered the carbon-to-nitrogen ratio of the decomposing litter. These results showed that warming did not alter the total litter mass-loss rates in this ecosystem, but that decomposition patterns were affected through more nuanced changes to both the biological and physical environment of dryland soils.

Klebsormidin A and B, Two New UV-Sunscreen Compounds in Green Microalgal Interfilum and Klebsormidium Species (Streptophyta) From Terrestrial Habitats.

The terrestrial green algal members of the genera Interfilum and Klebsormidium (Klebsormidiophyceae, Streptophyta) are found in biological soil crusts of extreme habitats around the world where they are regularly exposed, among other abiotic stress factors, to high levels of ultraviolet radiation (UVR). As a consequence those species synthesize and accumulate either one or two mycosporine-like amino acids (MAAs), but with a missing structural elucidation up to now. Therefore, in the present study both MAAs were chemically isolated and structurally elucidated. The two new compounds exhibit absorption maxima of 324 nm. MAA 1 has a molecular weight of 467 and MAA 2 of 305, and the latter (MAA 2) was identified as N-(4,5-dihydroxy-5-(hydroxymethyl)-2-methoxy-3-oxocyclohex-1-en-1-yl)-N-methylserine using one- and two-dimensional 1H and 13C-NMR spectroscopy. MAA 1 contains an additional sugar moiety. As trivial names for these two novel MAAs we suggest klebsormidin A and klebsormidin B. Different species from all previously described phylogenetic clades of Klebsormidiophyceae were chemically screened for their MAA composition in aqueous extracts using RP−HPLC and LC−MS. The novel klebsormidin A was present throughout all clades and hence could be suitable as a chemotaxonomic marker. Additionally, controlled UVR−exposure experiments with all investigated species showed that MAA biosynthesis and intracellular enrichment is strongly induced by short wavelengths, supporting the function of these compounds as natural UV−sunscreen as well as explaining the cosmopolitan distribution and ecological success of Interfilum and Klebsormidium in terrestrial habitats.

Exchangeable cations and pH drive diversity and functionality of fungal communities in biological soil crusts from coastal sites of Victoria Land, Antarctica

Abstract Ice-free regions in coastal areas of Victoria Land, Antarctica, are patchily distributed, limited in extent and characterized by a simple vegetation of lichens and mosses, growing only for a short period during the austral summer. These organisms are associated with soil particles and microorganisms (e.g., algae, microfungi and bacteria) to make up biological soil crusts (BSCs), found worldwide in cold and/or arid and semi-arid regions, where plant growth is impaired. Despite BSCs being among the most widespread ecosystems throughout coastal ice-free areas of continental Antarctica, fungal components of these communities have received little focus. Through ITS1 DNA metabarcoding of samples from 17 sites of six different localities from 73 to 77°S, in a distance scale from 29 to 411 km among different sites, we provide insights into the diversity, community composition, and functionality of fungal communities of these peculiar ecosystems, deepening our knowledge on how they are related to different edaphic variables (i.e. chemical properties and texture). Although fungal richness was low (59 ± 27 OTUs per sample), we found numerous previously unsequenced, putatively unknown fungal species representing a great part of the sampled communities. Community composition was spatially auto-correlated and appeared to be driven by site-specific differences in environmental conditions, particularly edaphic factors, such as exchangeable cations and pH. These results are of particular interest, as they give a wide characterization of the parameters determining soil colonization in a such limiting environment, especially in the light of global changes that are expected to deeply modify the conditions of this environment.

Induced biological soil crusts and soil properties varied between slope aspect, slope gradient and plant canopy in the Hobq desert of China

Cyanobacterial inoculation can accelerate the formation of induced biological soil crusts (IBSCs) and is suggested as an effective strategy for desertification reversal. However, previous studies concerning the spatial distribution of IBSCs at the micro scale are insufficient. In this study, IBSCs distributed in microhabitats differing in slope aspect, slope gradient and plant cover were investigated to reveal the effects of microhabitats on soil properties and IBSC development. There are significant differences in soil environmental factors including microclimates and soil physical properties, and soil component factors including SOC, TN, TP and dissolved organic matter components among sites with different microhabitats. Compared with IBSCs on south-facing slopes and in interspaces, those under plant cover and on north-facing slopes were characterized by higher biomass and moss abundance, indicating later successional stages. The relative contributions of microhabitat characteristics to the variance in environmental conditions and soil properties were slope aspect (59.5%) > shrub cover (13.8%) > slope gradient (6.2%). Furthermore, these environmental and soil component factors contributed equally and interactively to IBSC development. Our findings reveal that soil environmental factors and soil composition affected by microhabitats drive the distinct development of IBSCs in interactive and essential ways. More attention should be paid to these microhabitat-related soil factors in the IBSC rehabilitation and maintenance engineering.

Network analysis reveals the strengthening of microbial interaction in biological soil crust development in the Mu Us Sandy Land, northwestern China

Although studies examining changes in the structure and diversity of microbial communities in biological soil crusts (BSCs) have increased, microbial interactions in BSCs are not currently fully understood. In this study, we applied a random matrix theory (RMT)-based network approach to construct bacterial, fungal and bacteria-fungal interaction networks for the four developmental stages of BSCs (bare sand, physical crusts, algae crusts and moss crusts) in the Mu Us Sandy Land, northwestern China. Our results showed that Firmicutes, Proteobacteria, Cyanobacteria and Actinobacteria were the keystone phylum in bacterial networks in the four developmental stages, respectively. Ascomycota was the keystone phylum in the fungal networks in all stages, and Basidiomycota was a further keystone phylum in the algae and moss crust networks. With the development of BSCs, complexity in bacterial and fungal networks increased, becoming more clustered and connected, indicating a strengthened pattern in microbial interactions with BSC development. Positive links dominated in all networks, showing that microbial synergism was important in the development of BSCs. Interestingly, with the development of BSCs, the proportion of negative links in bacterial networks increased and they decreased in fungal networks, suggesting more inter-community competition was present in the bacterial communities and less inter-community competition was present in the fungal communities. Environmental factors, especially total carbon and total organic carbon, constrained most bacterial and fungal communities, respectively. Our findings provided a new insight into understanding BSC developmental mechanisms and ecological functions in a desert ecosystem composed of a sandy land landscape in arid and semi-arid regions.

Dictyosphaerium-like morphotype in terrestrial algae: what is Xerochlorella (Trebouxiophyceae, Chlorophyta)?1.

Several strains of terrestrial algae isolated from biological soil crusts in Germany and Ukraine were identified by morphological methods as the widely distributed species Dictyosphaerium minutum (=Dictyosphaerium chlorelloides). Investigation of the phylogeny showed their position unexpectedly outside of Chlorellaceae (Trebouxiophyceae) and distantly from Chlorella chlorelloides, to which this taxon was attributed after revision of the genus Chlorella based on an integrative approach. SSU rRNA phylogeny determined the position of our strains inside a clade recently described as a new genus of the cryptic alga Xerochlorella olmiae isolated from desert biological soil crusts in the United States. Investigation of the morphology of the authentic strain of X. olmiae showed Dictyosphaerium‐like morphology, as well as some other characters, common for our strains and morphospecies D. minutum. The latter alga was described as terrestrial and subsequently united with the earlier described aquatic representative D. chlorelloides because of their similar morphology. The revision of Chlorella mentioned above provided only one aquatic strain (D. chlorelloides), which determined its position in the genus. But terrestrial strains of the morphospecies were not investigated phylogenetically. Our study showed that the terrestrial D. minutum is not related to the morphologically similar D. chlorelloides (=Chlorella chlorelloides, Chlorellaceae), and instead represented a separate lineage in the Trebouxiophyceae, recently described as genus Xerochlorella. Therefore, revision of Xerochlorella is proposed, including nomenclatural combinations, epitypifications, and emendations of two species: X. minuta and X. dichotoma. New characters of the genus based on investigation of morphology and ultrastructure were determined.

Improved extraction of multiclass cyanotoxins from soil and sensitive quantification with on-line purification liquid chromatography tandem mass spectrometry

Cyanotoxins are associated with harmful cyanobacterial blooms, but also exist in biological soil crusts and soils irrigated with cyanobacteria-contaminated water. To achieve an accurate analysis of cyanotoxins in soil, effective extraction, purification and determination methods are imperative. The most challenging aspect is extracting cyanotoxins from soil, due to their tendency to bind strongly to the soil matrix. We used a methanol-ammonium acetate solution to efficiently extract 17 cyanotoxins (microcystins, cylindrospermopsin, anatoxins, anabaenopeptins and cyanopeptolin) from soil. The extract was purified by on-line solid-phase extraction coupled with ultra-high-performance liquid chromatography tandem mass spectrometry. The optimized procedure involved two ultrasonication cycles of 15 min with 4 mL of methanol + 200 mM ammonium acetate, which recovered 60% to >90% of the added cyanotoxins from five soils with diverse organic matter, pH and texture. The method improved extraction by up to 10 times compared to a methanol/water solution. Linearity, accuracy and precision were validated on matrix-mixed soil with surrogate microcystin and cylindrospermopsin internal standards. Limits of detection were 0.001–0.3 ng g−1, depending on the cyanotoxins. The method was used to analyze cyanotoxins in 25 field-collected soils from Quebec, Canada. Out of the 25 soil samples, 11 soils had at least one cyanotoxin, and up to 8 different cyanotoxins were detected in one soil. The sum of all microcystins congeners was from 0.02 to 31 ng microcystins g−1 soil. We also detected anabaenopeptin, the first reported occurrence of this cyanotoxin in soil.

Niche Partitioning with Temperature among Heterocystous Cyanobacteria (Scytonema spp., Nostoc spp., and Tolypothrix spp.) from Biological Soil Crusts.

Heterocystous cyanobacteria of biocrusts are key players for biological fixation in drylands, where nitrogen is only second to water as a limiting resource. We studied the niche partitioning among the three most common biocrust heterocystous cyanobacteria sts using enrichment cultivation and the determination of growth responses to temperature in 30 representative isolates. Isolates of Scytonema spp. were most thermotolerant, typically growing up to 40 °C, whereas only those of Tolypothrix spp. grew at 4 °C. Nostoc spp. strains responded well at intermediate temperatures. We could trace the heat sensitivity in Nostoc spp. and Tolypothrix spp. to N2-fixation itself, because the upper temperature for growth increased under nitrogen replete conditions. This may involve an inability to develop heterocysts (specialized N2-fixing cells) at high temperatures. We then used a meta-analysis of biocrust molecular surveys spanning four continents to test the relevance of this apparent niche partitioning in nature. Indeed, the geographic distribution of the three types was clearly constrained by the mean local temperature, particularly during the growth season. This allows us to predict a potential shift in dominance in many locales as a result of global warming, to the benefit of Scytonema spp. populations.

Data variability or paradigm shift? Slow versus fast recovery of biological soil crusts-a review

Biological soil crusts, known also as biocrusts, provide valuable ecosystem services, especially in arid and semiarid regions. They may affect geomorphological (stability), hydrological (infiltration, evaporation), biochemical (carbon and nitrogen fixation) and ecological (germination and growth of vascular plants) processes, and their disturbance may have important ecological consequences. The common view, as reflected in hundreds of papers, regards biocrusts as having extremely slow recovery with characteristic time of up to hundreds and even thousands of years. Long recovery time implies that disturbance or climate change may have severe long-lasting consequences even once the conditions return to their initial state, triggering ample efforts to hasten biocrust recovery by inoculation. We critically analyze available estimates of the crust recovery time and present systematic measurements and theoretical considerations that attest to relatively rapid recovery of the crusts. We conclude that the likely recovery time of cyanobacterial crusts is 5–10 years, while that of lichen- and moss-dominated crusts is 10–20 years. Subsequently, costly and potentially negative effects to the ecosystem during inoculation should be weighed against the fast natural recovery of the biocrusts.

Halophilic Algal Communities in Biological Soil Crusts Isolated From Potash Tailings Pile Areas

Mining potash for fertilizer produces vast amounts of highly saline waste that is deposited in potash tailings piles. Rainfall washes the salts out, affecting the surrounding ecosystems. Only salt-tolerant organisms occur close to the piles, since other species cannot survive in these hypersaline conditions. Halophytic plant communities around tailings piles have been well investigated. However, studies exploring the biodiversity of the space behind the vegetation line that separates suitable salinities for plant growth from hostile conditions are rare. On top of the tailings piles, only micro-organisms thrive. This study, for the first time, explored the microalgae and cyanobacteria in biocrusts that in-habit potash tailings pile areas between the vegetation line and the pile body. Two biocrust types were studied: young biocrusts at or close to the tailings piles, and established biocrusts situated in the near surroundings. The estimated abundance of green algae, cyanobacteria and diatoms was studied using a direct microscopy approach, followed by the isolation and establishment of unialgal strains and morphological species determinations. Soil environmental characteristics were analyzed. Soil samples showed ECSat (electrical conductivity) values that drastically exceeded the scales commonly used to describe soil salinity, indicating extremely saline conditions. Indeed, the isolate composition was shaped by soil salinity parameters. Soil ECSat of young biocrusts tended to be higher than in estab-lished biocrusts, and filamentous green algae were most abundant. In contrast, established biocrusts tended to have a lower ECSat and were mostly dominated by filamentous cyanobacteria. Algal and cyanobacteria isolate composition differed significantly in young and established biocrusts, although the species number did not. Some of the salt-tolerant algal strains are assumed to be candidates for the formation of artificial biocrusts on the surface of the tailings. Attempts to “green” the piles by the establishment of higher plants to trap rainwater and therefore reduce the salt-output are difficult to apply. Plants require a thick layer of substrate to reduce the salinity, and the substrate easily erodes on the steep slopes. However, microalgae isolated from potash tailings pile areas seem promising, since they can survive on a thinner substrate layer and are already adapted to these hypersaline conditions.

Influence of management intensity and environmental conditions on microbiota in biological soil crust and crust-free soil habitats of temperate forests

The microbiota in three distinct terrestrial habitats (biological soil crusts – BSC, crust-adhering soil beneath BSC – trans, and crust-free soil close to BSC – soil) was studied in 33 temperate forest stands differing in management intensity (ForMI). Specific lipid fractions and respective marker fatty acids were used to determine microbial biomass and community structure (phospholipid fatty acids – PLFA), energy reserves (neutral lipid fatty acids – NLFA), and community level lipid profiles (CLLP) of nematodes and enchytraeids. The density and diversity of nematode fauna were additionally determined morphologically. The highest total amounts of PLFA and NLFA occurred in the BSC, followed by soil and trans habitats, indicating stronger effects of habitats than forest management intensity. This corresponds to the distribution pattern of bacterial PLFA that dominated the soil microbiota. The highest nematode population density occurred in the BSC, followed by soil and trans. The BSC was dominated by bacterial feeders and omnivores, while plant feeding nematodes were most frequent in the crust-free soil habitat. The highest biomass of photoautotrophs also occurred in the BSC, followed by the crust-adhering and crust-free soil habitats. Redundancy analysis indicated strong effect of ForMI and total N on soil PFLAs and NFLAs across habitats. The C:N and C:S ratios were important for the separation of NLFAs while P:S accounted for the separation of PLFAs. Bacterial and fungal PLFAs largely separated the microbial community across habitats, and particularly between BSC and trans habitats. The separation of nematodes and enchytraeids by CLLP was less pronounced, and most distinct between the crust-free soil and BSC or crust-adhering soil habitats. Overall, BSC and crust-adhering soil habitats provide different suitability for microbiota, resulting in specifically adapted communities that are shaped by the management intensity and nutrient availability.

Nitrogen pools in soil covered by biological soil crusts of different successional stages in a temperate desert in Central Asia

Biological soil crusts (BSCs) are a primary source of nitrogen (N) in deserts through N-fixation. N-fixation rates may be determined by the species present within BSCs, and environmental factors like temperature and moisture, which vary seasonally. These same factors may also govern dynamics of within-soil N transformations. Few studies have explored the dynamics of different N forms in response to seasonal microclimate variations in BSCs, especially across both the growing season and the snow-covered season (winter). In this study, monthly changes in multiple soil N pools across a full year and beneath three soil cover types – bare soil, cyanobacteria BSC, and lichen BSC – were assessed across a full year in the Gurbantunggut Desert, Central Asia. We focused on multiple organic and inorganic N pools including: total N, alkali-hydrolyzable N, DON, inorganic N (NH4+-N, NO3−-N), free amino acids, and microbial biomass N. We found that different N forms had divergent trends during the year, peaked in different months, and showed non-synchronous responses related to seasonal temperature and moisture patterns. Most N forms were most abundant in lichen BSC > cyanobacteria BSC > bare soil, although significant differences were only observed in a few months. In the growing season, available N forms such as soil DON and inorganic N were related to both water and temperature. In winter, available N was strongly related to temperature variability prior to the sampling dates. The high NH4+-N/NO3−-N in the early growing season suggest that N fixation or N mineralization were highest at this time. Our results indicate non-synchronous availability of different N forms, and elevated N availability beneath lichen BSCs, which may maintain the diverse N uptake requirements for different plant species.

Dynamic expression of intra- and extra-cellular proteome and the influence of epiphytic bacteria for Nostoc flagelliforme in response to rehydration.

Nostoc flagelliforme is well known for its strong ecological adaptability in inhabiting desert biological soil crusts. However, the mechanism of its recovery from quiescent to active state after prolonged dormancy remains poorly characterized. Especially how exoproteome be related to the adaptive strategies and participate in the microalgae-bacteria interaction. In the present work, we analysed the intra- and extra-cellular proteome of N. flagelliforme over a complete rehydration period both in sterilization and in natural condition for the first time. The protein expression profile for N. flagelliforme has more fluctuations during the first 1 h after wetting but been relatively steady after fully hydrated. According to the extracellular proteomic datasets, we found a dynamic secretion of various extracellular hydrolytic enzymes and membrane transport proteins, which were related to peptidoglycan digestion and nutrient exchange respectively. Two-hundred and thirteen differentially expressed proteins induced by sterilization also reflect variation in nutrient exchange and highlight symbiosis between N. flagelliforme and surrounding bacteria. We also identified 112 phosphopeptides and 217 phosphorylation site of 95 protein of hydrated N. flagelliforme. The time course datasets we present here will be a reference for understanding the molecular processes underlying N. flagelliforme resuscitation and its potential role in microbial community diversification and soil desertification control.