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This article is an editorial that discusses the development and ecological functions of biological soil crusts (biocrusts). Biocrusts are composed of microorganisms and play important roles in soil stabilization, microbial diversity, and ecosystem development. The editorial emphasizes the need for further research on biocrust communities and their impact on landscape-scale outcomes. It also highlights the ecological functions of biocrusts, such as reducing erosion and influencing biogeochemical cycles. The article concludes by discussing the importance of understanding biocrusts for ecological restoration and land management strategies. Another document provides a list of references for articles related to biological soil crusts, covering topics such as land degradation neutrality, ecological restoration, and the impact of biocrusts on microbial communities. The articles also explore the composition and response of biocrusts to climate change and physical disturbance, as well as their effects on soil properties and metabolic response to hydration. [Extracted from the article]

In arid and semiarid ecosystems, plant interspaces are frequently covered by communities of cyanobacteria, algae, lichens and mosses, known as biocrusts. These crusts often act as runoff sources and are involved in soil stabilization and fertility, as they prevent erosion by water and wind, fix atmospheric C and N and contribute large amounts of C to soil. Their contribution to the C balance as photosynthetically active surfaces in arid and semiarid regions is receiving growing attention. However, very few studies have explicitly evaluated their contribution to organic carbon (OC) lost from runoff and erosion, which is necessary to ascertain the role of biocrusts in the ecosystem C balance. Furthermore, biocrusts are not resilient to physical disturbances, which generally cause the loss of the biocrust and thus, an increase in runoff and erosion, dust emissions, and sediment and nutrient losses. The aim of this study was to find out the influence of biocrusts and their removal on dissolved and sediment organic carbon losses. One-hour extreme rainfall simulations (50 mm h-1) were performed on small plots set up on physical soil crusts and three types of biocrusts, representing a development gradient, and also on plots where these crusts were removed from. Runoff and erosion rates, dissolved organic carbon (DOC) and organic carbon bonded to sediments (SdOC) were measured during the simulated rain. Our results showed different SdOC and DOC for the different biocrusts and also that the presence of biocrusts substantially decreased total organic carbon (TOC) (average 1.80±1.86 g m-2) compared to physical soil crusts (7.83±3.27 g m-2). Within biocrusts, TOC losses decreased as biocrusts developed, and erosion rates were lower. Thus, erosion drove TOC losses while no significant direct relationships were found between TOC losses and runoff. In both physical crusts and biocrusts, DOC and SdOC concentrations were higher during the first minutes after runoff began and decreased over time as nutrient-enriched fine particles were washed away by runoff water. Crust removal caused a strong increase in water erosion and TOC losses. The strongest impacts on TOC losses after crust removal occurred on the lichen plots, due to the increased erosion when they were removed. DOC concentration was higher in biocrust-removed soils than in intact biocrusts, probably because OC is more strongly retained by BSC structures, but easily blown away in soils devoid of them. However, SdOC concentration was higher in intact than removed biocrusts associated with greater OC content in the top crust than in the soil once the crust is scraped off. Consequently, the loss of biocrusts leads to OC impoverishment of nutrient-limited interplant spaces in arid and semiarid areas and the reduction of soil OC heterogeneity, essential for vegetation productivity and functioning of this type of ecosystems.

Sewage sludge (SS) is widely used as a soil conditioner in agricultural soil due to its high content of organic matter and nutrients. In addition, inoculants based on soil microorganisms, such as cyanobacteria, are being applied successfully in soil restoration to improve soil stability and fertility in agriculture. However, the combination of SS and cyanobacteria inoculation is an unexplored application that may be highly beneficial to soil. In this outdoor experiment, we studied the ability of cyanobacteria inoculum to grow on degraded soil amended with different concentrations of composted SS, and examined the effects of both SS concentration and cyanobacteria application on carbon gain and soil stability. We also explored the feasibility of using cyanobacteria for immobilizing salts in SS-amended soil. Our results showed that cyanobacteria growth increased in the soil amended with the lowest SS concentration tested (5 t ha−1, on soil 2 cm deep), as shown by its higher chlorophyll a content and associated deeper spectral absorption peak at 680 nm. At higher SS concentrations, inoculum growth decreased, which was attributed to competition of the inoculated cyanobacteria with the native SS bacterial community. However, SS significantly enhanced soil organic carbon gain and tightly-bound exopolysaccharide content. Cyanobacteria inoculation significantly improved soil stability and reduced soil's wind erodibility. Moreover, it led to a decrease in the lixiviate electrical conductivity of salt-contaminated soils, indicating its potential for salt immobilization and soil bioremediation. Therefore, cyanobacteria inoculation, along with adequately dosed SS surface application, is an efficient strategy for improving carbon gain and surface stability in dryland agricultural soil. [ABSTRACT FROM AUTHOR]

Badlands are landforms that occur all over the World. In the Mediterranean region, badlands are found in both dry (arid and semi‐arid) and wet (subhumid and humid) environments, and are characterized by complex hydro‐geomorphological dynamics, high intense erosion processes and extreme sediment yield. Understanding the impact of Global Change is key to predict the on‐site and off‐site effects on badland dynamics, particularly its consequences on bedrock weathering, on sediment yield and delivery and on plant colonization. Here, conducting a systematic literature review, we analyzed an extensive database and identified the main climate‐drivers affecting the hydro‐geomorphological dynamics in Mediterranean badlands (based on non‐metric multidimensional scaling and structural equation modeling analysis). Later, we examined the main impacts expected from climate change forecasting in the near future, and we explored the interactions between badlands response to climate variation. In Mediterranean badlands, weathering processes are mainly related to wetting–drying cycles and freeze–thaw cycles in dry and wet badlands, respectively. In both environments, rainfall amount appears as the main driver for runoff response, and rainfall amount and rainfall intensity for erosion dynamics. Future climate scenarios forecast a decrease in annual rainfall, number of rainfall events and frost days, and in soil moisture, and an increase in rainfall intensity. These changes will have direct hydro‐geomorphological implications with direct and indirect effects on badland dynamics. This may result in a decrease in annual runoff in dry badlands, but the occurrence of more frequent extreme events would increase soil erosion and could negatively affect biological soil crust. In wet badlands, weathering and erosion processes may decrease, and a stabilization of the slopes, with consequently improved vegetation growth, may be expected. In addition, the forecasted changes must be taken into account, especially considering the possible off‐site effects of these extreme environments. [ABSTRACT FROM AUTHOR]

Land degradation in drylands is a drawback of the combined action of climate change and human activities. New techniques have been developed to induce artificial biocrusts formation as a tool for restoration of degraded drylands, and among them soils inoculation with cyanobacteria adapted to environmental stress. Improvement of soil properties by cyanobacteria inoculation is largely related to their ability to synthesize exopolysaccharides (EPS). However, cyanobacterial EPS features [amount, molecular weight (MW), composition] can change from one species to another or when grown in different conditions. We investigated the differences in growth and polysaccharidic matrix features among three common biocrust-forming cyanobacteria (Nostoc commune, Scytonema javanicum , and Phormidium ambiguum), when grown in liquid media and on sandy soil microcosms under optimal nutrient and water, in controlled laboratory conditions. We extracted and analyzed the released EPS (RPS) and sheath for the liquid cultures, and the more soluble or loosely-bound (LB) and the more condensed or tightly-bound (TB) soil EPS fractions for the sandy soil microcosms. In liquid culture, P. ambiguum showed the greatest growth and EPS release. In contrast, on the sandy soil, S. javanicum showed the highest growth and highest LB-EPS content. N. commune showed no relevant growth after its inoculation of the sandy soil. A difference was observed in terms of MW distribution, showing that the higher MW of the polymers produced by P. ambiguum and S. javanicum compared to the polymers produced by N. commune , could have had a positive effect on growth for the first two organisms when inoculated on the sandy soil. We also observed how both RPS and sheath fractions reflected in the composition of the soil TB-EPS fraction, indicating the role in soil stabilization of both the released and the cell attached EPS. Our results indicate that the features of the polysaccharidic matrix produced by different cyanobacteria can influence their growth success in soil. These results are of great relevance when selecting suitable candidates for large-scale cyanobacteria applications in soil restoration. [ABSTRACT FROM AUTHOR]

The practice of "cyanobacterization" (soil inoculation with cyanobacteria) has been shown to be effective in increasing soil fertility and physical stability in natural and agricultural soils, but little is known about its utility for the recovery of burned soils. To partly fill this knowledge gap, we inoculated two cyanobacterial species, Phormidium ambiguum and Scytonema javanicum, in two burned sterilized soils having contrasting properties, and incubated them under laboratory conditions for 45 days. The development of a cyanobacterial biocrust induced by the inoculum was evident and confirmed by the significant increase in chlorophyll a content compared to control soils. Hydrophobicity, surface penetration resistance, and exopolysaccharide content of the two soils were also evaluated. Cyanobacteria inoculation significantly decreased soil hydrophobicity, as assessed by the lower repellency index 15 days after the inoculation compared to the control soils. A significant increase in penetration resistance was recorded in the inoculated samples compared to control ones after 45 days of soil incubation. The effect of cyanobacteria inoculation depended on the characteristics of the burned soil, being more marked in the soil finer in texture, richer in organic carbon and nitrogen, and with lower initial soil hydrophobicity. In conclusion, this study points to the potential of cyanobacterization for the stabilization and recovery of soils in burned areas, which is one of the major concerns in postfire management to avoid net soil loss and major hydrogeological issues. [ABSTRACT FROM AUTHOR]

Globally, most bare-looking areas in dryland regions are covered by biocrusts which play a crucial role in modifying several soil surface properties and driving key ecosystem processes. These keystone communities face important threats (e.g. climate change) that place their conservation at risk and in turn the sustainability of the ecosystems they inhabit. Therefore, there is an urgent need to develop ecosystem management strategies to ensure their protection. However, to provide a solid path towards biocrust conservation, the understanding by stakeholders and governance structures of the ecological functions of these communities, their role as benefit providers, and the pressures threatening their important effects are indispensable. Whereas the ecological scope of biocrust has been widely studied in the last decades, the social dimension of their role remained unexplored. By reviewing literature in biocrusts from a social–ecological approach, here we identified knowledge gaps and new research areas that need to be addressed in order to produce scientific knowledge that better guides dryland conservation policies and actions. This research agenda is a prerequisite to advance biocrust conservation. [ABSTRACT FROM AUTHOR]

Biological soil crust, or biocrust communities, are the dominating life form in many extreme habitats, such as arid and semiarid badlands, where water scarcity and highly erodible substrates limit vegetation cover. While climate, soil and biotic factors have been described as environmental filters influencing biocrust distribution in such biomes, little is known about the effect of terrain attributes on creating specific microhabitats that promote or restrict biocrust colonization. This study aimed to identify the main terrain attributes controlling biocrust distribution in the driest badland system in Europe, the Tabernas Badlands (SE Spain). To do this, we analysed the influence of different terrain attributes related to landscape stability and microclimate formation on the spatial distribution of lichen and cyanobacteria, using field measurements and topographical information from a LiDAR survey. Our results showed that the spatial distribution of cyanobacteria‐dominated biocrusts, which are physiologically and morphologically adapted to extreme drought and high UVA radiation, was mostly associated with areas of high potential incoming solar radiation. The exception was bare south‐aspect hillslopes with very high sediment transport potential, where bare physically crusted soils were the dominant ground cover. Lichen‐dominated biocrusts, in contrast, colonized near the top of north‐aspect hillslopes, characterized by low potential incoming solar radiation and potential evapotranspiration, and their cover decreased downstream, as conditions became good enough for vascular plants. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Cyanobacteria are key microbes in topsoil communities that have important roles in preventing soil erosion, carbon and nitrogen fixation, and influencing soil hydrology. However, little is known regarding the identity and distribution of the microbial components in the photosynthetic assemblages that form a cohesive biological soil crust (biocrust) in drylands of Europe. In this study, we investigated the cyanobacterial species colonizing biocrusts in three representative dryland ecosystems from the most arid region in Europe (SE Spain) that are characterized by different soil conditions. Isolated cyanobacterial cultures were identified by a polyphasic approach, including 16S rRNA gene sequencing, phylogenetic relationship determination, and morphological and ecological habitat assessments. Three well-differentiated groups were identified: heterocystous-cyanobacteria (Nostoc commune, Nostoc calcicola, Tolypothrix distorta and Scytonema hyalinum), which play an important role in N and C cycling in soil; nonheterocystous bundle-forming cyanobacteria (Microcoleus steenstrupii, Trichocoleus desertorum, and Schizothrix cf. calcicola); and narrow filamentous cyanobacteria (Leptolyngbya frigida and Oculatella kazantipica), all of which are essential genera for initial biocrust formation. The results of this study contribute to our understanding of cyanobacterial species composition in biocrusts from important and understudied European habitats, such as the Mediterranean Basin, a hotspot of biodiversity, where these species are keystone pioneer organisms. [ABSTRACT FROM AUTHOR]

Abstract: Dryland vegetation is limited by water scarcity, and usually appears in the form of sparsely distributed patches within a heterogeneous unvegetated matrix often covered by biological soil crust. Biocrusts usually act as runoff sources, whereas vegetation acts as sinks, reinfiltrating most of the run‐on from upstream biocrusted areas. Alteration of biocrusts by human disturbances or climate change may exert a strong impact on soil erosion, promoting rill formation, increasing flow connectivity between source areas and reducing run‐on inputs to vegetation, strongly affecting ecosystem functioning. The role of biocrust runoff in vegetation productivity, which to date has not been studied in depth, must therefore be understood to predict the consequences of such changes. In this study, we analysed the response of Machrochloa tenacissima to run‐on exclusion for two years and compared it to the performance of plants of the same species receiving runoff from biocrusted source patches. The results showed that plants receiving run‐on had more photosynthetically active biomass, net C uptake rates and water‐use efficiency than plants under run‐on exclusion. Differences between treatments became wider over time, especially after rainfall, when the differences in water availability were greatest. These results lead to the conclusion that run‐on is a crucial water input for dryland vegetation. Any alteration of unvegetated areas usually covered by biocrust may have important effects on vegetation productivity similar to those from changes in precipitation pattern, and would result in a new, eco‐hydrological equilibrium of the whole ecosystem. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, soil inoculation with cyanobacteria has become one of the most promising biotechnological strategies for restoring soil functionality in degraded drylands because of their critical role in increasing soil fertility and preventing erosion. Nevertheless, in order to fully exploit this biotechnology on a large scale, it must still be shown whether inoculated cyanobacteria are capable of developing in soils with different physicochemical properties, and new candidates adapted to desert conditions must be explored. To evaluate the potential of cyanobacteria for restoring soil functions of degraded dryland soils, in this laboratory study, we analyzed the effect of inoculating three native N‐fixing species (Nostoc commune, Scytonema hyalinum, and Tolypothrix distorta), individually and as a consortium, on soil properties from three different semiarid ecosystems in southeast Spain. The biocrust colonization was monitored by determining chlorophyll a content (the typical surrogate used for biocrust biomass). Other methodologies, such as the analysis of soil spectral response and image classification were also applied for cover estimation of the biocrust. After 3 months, all inoculated soils showed cyanobacteria cover of up to 50%, lower albedo and higher chlorophyll a content. Cyanobacterial inoculation also improved soil functions, as they promoted a significant gain in total organic carbon and total nitrogen in all soils. Among inoculation treatments, Nostoc commune and the mixture of all three species promoted the most cyanobacteria coverage, chlorophyll content, and surface darkening, as well as organic carbon and total nitrogen gains in the soil, highlighting their excellent performance in biocrust development. [ABSTRACT FROM AUTHOR]

Land degradation by erosion is especially important in drylands, which are among the most vulnerable to disturbance by human activity or climate change. Biocrusts are an essential surface component of these ecosystems and one of the most important contributors to surface resistance and stability, and therefore, keeping soil fertile in these nutrient-limited-environments. Loss of biocrusts can result in increased sediment losses and subsequent loss of soil organic carbon (SOC) and other soil resources, which are vital for vegetation and general ecosystem functioning. Despite their importance, the consequences of biocrust loss on sediment and SOC losses in drylands have been poorly analysed. In this study, we examined the influence of two biocrust types (cyanobacteria and lichen-dominated biocrusts) and biocrust removal on runoff and sediment yield, from natural rainfall during one hydrological year in a semiarid badlands catchment (Tabernas, SE Spain). The influence of biocrust type and biocrust removal on SOC losses from water erosion (dissolved and sediment organic carbon losses, DOC and SdOC, respectively) was also analysed. Our results show that sediment yield significantly increased after biocrust removal, especially during the first rain after biocrust removal, when particles were left directly exposed to raindrop impact and easily washed away by runoff. Annual sediment yield was 465, 75 and 24 g m − 2 in biocrust-removed, cyanobacteria-covered and lichen-covered soil, respectively, and the first event represented 87% of annual sediment losses on biocrust-removed plots. Biocrust removal was accompanied by a significant increase in both DOC and SdOC mobilisation. Total organic carbon (TOC) mobilisation was the highest in soils where the biocrust had been removed and decreased as the biocrust was more developed. Annual TOC mobilisation was 10.2, 3.0 and 1.4 g m − 2 in biocrust-removed, cyanobacteria-covered and lichen-covered soil, respectively. TOC mobilisation was mainly driven by sediments and thus, 89% of annual TOC mobilisation occurred during the first rain after biocrust removal. The high sediment and SOC losses recorded after biocrust removal emphasize the importance of biocrust conservation for avoiding the loss of soil resources and maintaining fertility in interplant soils in drylands. [ABSTRACT FROM AUTHOR]

Biocrusts play crucial roles in hydrological processes by controlling soil water availability and regulating water redistribution from source to sink areas. Most studies have examined the influence of biocrusts on isolated components of the soil water balance, but few have addressed this matter from an integrated point of view, involving their influence on all components together. Such integration is crucial to elucidate the overall effects of biocrusts on the soil water balance. The aim of this study was to review the role of biocrusts in the soil water balance, by examining their influence on infiltration, evaporation and soil moisture at plot scale, in two contrasting ecosystems of SE Spain. Our results show that biocrust infiltration was higher in flat soils with sandy loam texture than in steep soils with silty loam texture. The influence of biocrusts on infiltration depended on rainfall intensity. Biocrusts increased infiltration with respect to biocrust-removed soils during low intensity rainfalls but showed similar or even lower infiltration than biocrust-removed soils during high-intensity events. As a result of the increase in infiltration and a decrease in evaporation during wet cold periods, biocrusts increased soil moisture when compared with biocrust-removed soils. However, during warm periods, biocrusts and biocrust-removed soils lost water very quickly, thus resulting in similar water losses and moisture content under both types of surfaces. We conclude that biocrusts increase water input by increasing infiltration and soil moisture, and reduce water output by reducing soil evaporation, thus eventually enhancing the available water to plants. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Humans consume much more energy than that merely needed to maintain metabolism. • Human exploitation generates tension with the ecosystem self-organization. • Human exploitation shifts the scale at which physical factors exert their control. • However, in turn, the landscape affects humans, generating adaptations. • The Ecodesert SI facilitates the understanding of Prof Puigdefabregas' contribution. [ABSTRACT FROM AUTHOR]

Arid and semi-arid ecosystems are characterized by patchy vegetation and variable resource availability. The interplant spaces of these ecosystems are very often covered by cyanobacteria-dominated biocrusts, which are the primary colonizers of terrestrial ecosystems and key in facilitating the succession of other biocrust organisms and plants. Cyanobacterial biocrusts regulate the horizontal and vertical fluxes of water, carbon and nutrients into and from the soil and play crucial hydrological, geomorphological and ecological roles in these ecosystems. In this paper, we analyze the influence of cyanobacterial biocrusts on water balance components (infiltration-runoff, evaporation, soil moisture and non-rainfall water inputs (NRWIs)) in representative semiarid ecosystems in southeastern Spain. The influence of cyanobacterial biocrusts, in two stages of their development, on runoff-infiltration was studied by rainfall simulation and in field plots under natural rainfall at different spatial scales. Results showed that cover, exopolysaccharide content, roughness, organic carbon, total nitrogen, available water holding capacity, aggregate stability, and other properties increased with the development of the cyanobacterial biocrust. Due to the effects on these soil properties, runoff generation was lower in well-developed than in incipient-cyanobacterial biocrusts under both simulated and natural rainfall and on different spatial scales. Runoff yield decreased at coarser spatial scales due to re-infiltration along the hillslope, thus decreasing hydrological connectivity. Soil moisture monitoring at 0.03 m depth revealed higher moisture content and slower soil water loss in plots covered by cyanobacterial biocrusts compared to bare soils. Non-rainfall water inputs were also higher under well-developed cyanobacterial biocrusts than in bare soils. Disturbance of cyanobacterial biocrusts seriously affected the water balance by increasing runoff, decreasing soil moisture and accelerating soil water loss, at the same time that led to a very significant increase in sediment yield. The recovery of biocrust cover after disturbance can be relatively fast, but its growth rate is strongly conditioned by microclimate. The results of this paper show the important influence of cyanobacterial biocrust in modulating the different processes supporting the capacity of these ecosystems to provide key services such as water regulation or erosion control, and also the important impacts of their anthropic disturbance. [ABSTRACT FROM AUTHOR]

Chlorophyll a concentration (Chla) is a well-proven proxy of biocrust development, photosynthetic organisms' status, and recovery monitoring after environmental disturbances. However, laboratory methods for the analysis of chlorophyll require destructive sampling and are expensive and time consuming. Indirect estimation of chlorophyll a by means of soil surface reflectance analysis has been demonstrated to be an accurate, cheap, and quick alternative for chlorophyll retrieval information, especially in plants. However, its application to biocrusts has yet to be harnessed. In this study we evaluated the potential of soil surface reflectance measurements for non-destructive Chla quantification over a range of biocrust types and soils. Our results revealed that from the different spectral transformation methods and techniques, the first derivative of the reflectance and the continuum removal were the most accurate for Chla retrieval. Normalized difference values in the red-edge region and common broadband indexes (e.g., normalized difference vegetation index (NDVI)) were also sensitive to changes in Chla. However, such approaches should be carefully adapted to each specific biocrust type. On the other hand, the combination of spectral measurements with non-linear random forest (RF) models provided very good fits (R2 > 0.94) with a mean root mean square error (RMSE) of about 6.5 µg/g soil, and alleviated the need for a specific calibration for each crust type, opening a wide range of opportunities to advance our knowledge of biocrust responses to ongoing global change and degradation processes from anthropogenic disturbance. [ABSTRACT FROM AUTHOR]

Cyanobacteria have been used as inoculants in dryland soils to promote biological soilcrust (or biocrust) recovery and restore vital soil functions. Their viability obeys totheir high resilience to stressful conditions and their reported beneficial effectson soil properties. Cyanobacteria from dry environments are characterized by ahigh capacity to synthesize large amounts of exopolysaccharides (EPS) that play afundamental role in the survival of cyanobacteria in these extreme habitats and areresponsible of many soil functions. Cyanobacterial EPS increase soil organic matter andnutrient content, thus improving soil fertility, and greatly enhance soil stability, thusconferring a high resistance to soils to erosive forces by water and wind. CyanobacterialEPS are characterized by a different degree of condensation, molecular weight(MW) distribution and monosaccharidic composition, which condition the role ofthe cyanobacterial polysaccharidic matrix in the soil. A few studies have analyzedthe MW distribution and chemical characteristics of the polysaccharidic matrix innatural and induced biocrusts, and most of them have been carried out on sandysoils. However, the characteristics of the cyanobacterial polysaccharidic matrix maygreatly depend on soil type. The objective of this study was to examine the EPSsynthesis of two common arid soil cyanobacterial species, Phormidium ambiguum (nonN-fixing) and Scytonema javanicum (N-fixing) in both liquid culture and a solidsubstrate, and to analyze the MW distribution and monosaccharidic composition of thepolysaccharidic matrix developed in different soil types after inoculation with the twocyanobacterial species. We found that P. ambiguum showed a faster growth and a higherEPS synthesis in liquid culture, whereas S. javanicum showed a higher growthand led to a higher EPS content in the soil. EPS characterization in the inducedbiocrusts revealed important differences between species and soil types. S. javanicumled to a higher synthesis of more soluble and less condensed EPS (loosely-boundEPS), which were mainly composed of low MW weight (<50 kDa). P. ambiguumpromoted a higher amount of more condensed EPS (tightly-bound EPS), mainlycomposed of high MW molecules (1100-2000 kDa), which likely contributed to soilparticle consolidation and explain the higher surface resistance found in the soilsinoculated with this cyanobacterium. Inoculated soils showed a complex composition,with a high number of monosaccharides (from 11 to 12). Glucose was the mostabundant monosaccharide in all soil types, representing up to 90% of EPS in thesandy soil. In more complex soils (having higher EPS, organic carbon and nitrogencontents), galactose, mannose and xylose were also relatively abundant. On the whole,cyanobacterial species and soil type influenced the macromolecular distribution and chemicalcomposition of the biocrust polysaccharidic matrix, which is expected to have animportant role in biocrust succession and evolution of soil properties in dryland soils. [ABSTRACT FROM AUTHOR]

Cyanobacteria are widespread prokaryotic organisms that represent feasible biotechnological tools to set up valid approaches to counteract desertification. Their peculiar physiological traits, and their resilience to abiotic stresses, allow their application on abiotically constrained soils to trigger their stabilization. A successful cyanobacteria inoculation results in the formation of cyanobacterial biocrusts, complex microbial communities characterized by tangled filament meshes imbued in a matrix of self-secreted extracellular polysaccharides (EPS) that keep loose sediments and aggregates firmly in place. However, the capability to form stable cyanobacterial biocrusts is not common to all the species, and a mix of factors can hamper the process, notably inoculum amount, and substrate characteristics. The aim of this work was to assess the influence of inoculum quantity and substrate granulometry on the physical stability of cyanobacterial biocrusts induced by inoculating the strain Leptolyngbya ohadii in a microcosm experiment, under laboratory conditions. After applying three different initial inoculum amounts on two different sand granulometries (medium and coarse sand), we assayed aggregate stability, physical stability and surface hydrophobicity on the resulting biocrusts during a 30-day incubation. Also, the features and the role of the EPS synthesized by L. ohadii were studied following their isolation, characterization, and direct application on the sand. The two EPS fractions produced by the strain, one more soluble and easily released in the surrounding medium (released polysaccharides, RPS) and one solidly attached to the filaments (glycocalyx EPS, G-EPS), were separately tested. Cyanobacterial biocrusts visibly formed in all the microcosms after 15 days. However, we observed a strong effect of sand granulometry in affecting aggregate stability and tensile strength, both of which appeared weaker on coarse sand. A higher amount of initial inoculum was necessary to produce stable biocrusts on coarse sand compared to medium sand. Also, we observed how the inoculation of EPS alone did not sort most of the significant effects that we detected by inoculating the whole culture, pointing at the importance of the action of the cyanobacterial filaments in soil conglomeration. However, a significant increase in physical stability was achieved by inoculating G-EPS on medium sand, suggesting the involvement of this fraction in biocrusts structuration. This work analyzes for the first time the effects of the variable grain size and inoculum amount in the achievement of physically stable biocrusts by cyanobacteria inoculation. The results that we obtained are useful in improving and optimizing the process of biomass preparation and dispersion for future indoor and outdoor studies. • Cyanobacterization success requires an optimal initial inoculum amount. • Medium sand is more conductive to biocrust stability than coarse sand. • L. ohadii EPS alone cannot elicit sand aggregate stability and water repellency. • G-EPS appears as the fraction more involved in biocrust physical stability. [ABSTRACT FROM AUTHOR]

Atmospheric methane (CH 4) and carbon dioxide (CO 2) concentration have been increasing during the last several centuries due to changes in agricultural practices and other anthropogenic activities. Both greenhouse gases (GHGs), have a significant impact on the Earth's radiative balance. GHG effluxes of CH 4 and CO 2 were measured in a warm Mediterranean wetland in south of Spain. The dominant vegetation cover at the site was by common reed (Phragmites australis) and the measurements were done during short measurement campaign in early autumn 2015. Gas-flux measurements were carried out applying two methods, the eddy covariance (EC) technique and the chamber method (CM). These two methods representing different ecosystem subsets, with EC representing the plant/ecosystem subset and CM representing the water/soil subset. In our measurement campaigns using CM, CH 4 emissions ranged from 7.2 to 17.7 mg CH 4 -C m−2 d−1 and CO 2 emissions from 0.53 to 1.27 g CO 2 -C m−2 d−1. When using EC, the average fluxes of CH 4 and CO 2 were 31.4 mg CH 4 -C m−2 d−1 and 1.32 g CO 2 -C m−2 d−1, respectively. Relationships between gas fluxes (CO 2 and CH 4) measured by the EC method were quite closely correlated with photosynthetically active solar radiation. Our results showed higher CO 2 carbon released from the water/soil ecosystem subset in comparison to plants subset. On the other hand, the estimated CH 4 carbon balance for the plant/ecosystem subset was about twice that of the water/soil ecosystem subset. Overall, we showed that EC and CM methods cover different areas making EC advantageous for integrated measurements over larger areas, while the CM approach is suitable for local and spatially well constrained flux measurements. Hence, EC and CM methods should be seen as complementary rather than fully comparable methods. • CH 4 and CO 2 were measured in Phragmites australis wetland by EC and CM in autumn. • Average fluxes of CH 4 and CO 2 were 31.4 mg CH 4 -C m−2 d−1 and 1.32 g CO 2 -C m−2 d−1. • Higher amount of CO 2 carbon emissions from the water/soil ecosystem level • CH 4 carbon emissions at plant ecosystem level were higher than water/soil level. • EC and CM methods should be seen as supplementary rather than comparable methods. [ABSTRACT FROM AUTHOR]

In most of non-vegetated areas from drylands, soils are colonized by biocrusts, and although they represent a small fraction of the soil profile, they strongly affect several soil surface properties, such as porosity, available nitrogen and carbon content, hydrophobicity or micro-topography. The influence of BSCs on these soil properties has effects on numerous ecosystem processes, including water retention and runoff generation. Previous studies on the hydrological and erosive response of soils covered by biocrusts have highlighted the role of soil surface roughness as a key variable for understanding the influence of biocrusts on runoff and erosion, but biocrusts' effects on surface micro-topography varies depending on crust water content. Biocrusts can absorb large amounts of water in a short period of time, increasing their volume and modifying surface micro-topography, this change depending on biocruts type and development. A correct characterization of these surface variations may increase the knowledge about hydrological response of biocrusts, and for this reason, accurate ground level measurements of biologically crusted surfaces are essential. The objective of this study is to analyze the effect of wetting on surface micro-topography of biologically crusted soils. To achieve this objective, different crust types were scanned in the laboratory with high resolution laser scanner. Five samples were collected for each of the 4 different crust types (bare soil, cyanobacteria biocrust, and two different lichen biocruts). Two different scans were made in each sample, in dry and wet conditions. Random roughness (RR) was calculated for data from every scan, and the RR indexes obtained before and after wetting were compared. According with our initial hypothesis, an increase in surface height and surface roughness up to 0.24 and 0.20 mm respectively was observed in more developed lichen biocruts, under wet conditions respect to dry ones. These differences, despite being very subtle, could exert strong implications on runoff generation, and water evaporation, and show the complex interactions between biocruts, surface micro-topography and water fluxes. [ABSTRACT FROM AUTHOR]

• This biocrust special issue is a collection of 27 papers from 12 countries worldwide. • Various topics in soil-biocrust interactions in drylands are included and discussed. • Major topics include biocrust effects on soil hydrology, erosion, C, and biodiversity. • Biocrust and functional responses to physical disturbance and climate change are emphasized. • Biocrust conservation and restoration are considered important in combatting soil and land degradation. Biocrusts are photosynthetic biotic communities of cryptogams and microbes that aggregate minerals at the soil surface in many ecosystems. Due to their high tolerance to harsh environments, biocrusts are present in a wide range of habitats, but are especially representative ground covers in regions with restricted vegetation growth, such as drylands (hyperarid, arid, semiarid, and dry subhumid regions) where water is a limiting factor, or high latitude or altitude regions where cold is a limiting factor. Since biocrusts fulfill a large range of ecological roles particularly in modifying soil properties and regulating functions, their rehabilitation and management is believed to be a promising measure for combating land degradation. We organized this article collection to further highlight the importance of biocrusts and their fundamental roles in reshaping soil properties and multifunctionality in drylands and other ecosystems, and to elucidate the ways in which global change factors are influencing biocrust-soil systems. The special issue brings together 27 research articles pertinent to soil-biocrust interactions or biocrust response to global change and disturbance from 12 countries worldwide (10 papers from China, 6 papers from the USA, 2 papers from Spain, 2 papers from Australia, in addition to studies from Antarctica, Argentina, Brazil, Iceland, Iran, Mexico, Norway, South Africa, and Sweden). The discussed topics include biocrust roles in regulating soil hydrology (6 papers), reducing soil erosion (4 papers), affecting soil carbon fixation and respiration (2 papers), and influencing soil microbial biodiversity (5 papers). The responses of biocrusts themselves and their functions to trampling disturbance (2 papers), land use shifts (2 papers), and climate change (5 papers) are also emphasized. On the whole, we highlight the capability of biocrusts in reshaping most properties of surface soil, acting as engineers and architects of surface soil properties, functions, and processes in dryland or other harsh environments, and we recognize the necessity of their protection and consideration as valuable nature-based measures to combat soil and land degradation. [ABSTRACT FROM AUTHOR]