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Mineral dust and sea spray aerosol represent important sources of ice-nucleating particles (INPs), the minor fraction of aerosol particles able to trigger cloud ice crystal formation and, consequently, influence multiple climate-relevant cloud properties including lifetime, radiative properties and precipitation initiation efficiency. Mineral dust is considered the dominant INP source in many parts of the world due to its ice nucleation efficiency and its sheer abundance, with global emission rates of up to 4700 Tg a−1. However, INPs emitted from the ocean surface in sea spray aerosol frequently dominate INP populations in remote marine environments, including parts of the Southern Ocean where cloud-resolving model simulations have demonstrated that cloud radiative properties are likely strongly controlled by INPs. Here we report INP concentrations measured in aerosol and seawater samples during Air Quality and Climate Change in the Arabian Basin (AQABA), a shipborne campaign that spanned the Red Sea, Gulf of Aden, Arabian Sea, Arabian Gulf and part of the Mediterranean. In aerosol samples collected within a few hundred kilometers of the first and second ranked sources of dust globally, the Sahara and Arabian Peninsula, INP concentrations ranged from 0.2 to 11 L−1 at −20 ∘C with observed ice-active surface site densities (ns) 1–3 orders of magnitude below levels predicted by mineral dust INP parameterizations. Over half of the samples (at least 14 of 26) were collected during dust storms with average dust mass concentrations between 150 and 490 µg m−3 (PM10), as simulated by the Modern-Era Retrospective analysis for Research and Application, version 2 (MERRA-2). The impacts of heat and peroxide treatments indicate that organics dominated the observed ice nucleation (IN) activity at temperatures ≥ −15 ∘C with proteinaceous (heat-labile) INPs frequently observed at high freezing temperatures >−10 ∘C. INP concentrations in seawater samples ranged between 3 and 46 mL−1 at −19 ∘C, demonstrating the relatively low INP source potential of seawater in the region as compared to seawater from multiple other regions reported previously. Overall, our results demonstrate that despite proximity to the Sahara and the Arabian Peninsula and the dominance of mineral dust in the aerosol sampled, existing mineral dust parameterizations alone would not skillfully represent the near-surface ns in the observed temperature regime (−6 to −25 ∘C). Future efforts to develop or improve representations of dust INPs at modest supercooling (≥-15 ∘C) would benefit from a characterization of the specific organic species associated with dust INPs. More generally, an improved understanding of the organic species associated with increased IN activity and their variability across dust source regions would directly inform efforts to determine whether ns-based parameterizations are appropriate for faithful representation of dust INPs in this sensitive temperature regime, whether region-specific parameterizations are required, or whether an alternative to the ns approach is necessary.

Isoprene is a chemical compound emitted naturally by soil, microorganisms, plants, and animals into the atmosphere. But plants are the largest emission source, and the amount of emission depends on plant species, weather conditions, and environmental conditions, including exposure to environmental stresses such as heat and drought. Isoprene is very reactive in the atmosphere and is involved in atmospheric physicochemical processes that can impact atmospheric chemistry, air quality, and regional climate. Quantification and understanding of the atmospheric processes influenced by isoprene result from a combination of observational experiments and estimates obtained from computational models. However, only a few long-term observational experiments have been conducted in the largest source of isoprene to the global atmosphere – the Amazon rainforest, and there are still uncertainties in the model estimates. Recent experiments have also shown that the models have greater uncertainty when estimating intra- and inter-annual variations in isoprene. This study aimed to improve our understanding of isoprene emission from a central Amazonian site by considering biological and environmental factors influencing emission on intra- and interannual time scales. By combining observational datasets, we adapted a widely used computational model of isoprene emission to observed conditions in the field. Our observations indicated that isoprene emission was not as high as the model estimated when the forest experienced environmental stress, such as heat and drought, in the 2015 El-niño year. In addition, observations revealed that the model performed well when diurnal variations were analyzed but not when long-term variations occurred. The performance for estimating intra- and inter-annual isoprene emission improved when the model was modified on two biological factors – (i) the amount of different leaf ages throughout the year and (ii) the emission rates of these different leaf ages. This shows that isoprene emission estimates can be improved when biological processes are mechanistically incorporated into the model.

Many dryland soils absorb atmospheric CO2 at night. Despite the relatively small annual carbon (C) uptake, ranging locally from 1 to 10 g C m-2, it may have large-scale effects, as drylands cover almost 45% of the Earth’s land surface. This process might contribute to the global missing C sink of 3.1 ± 0.9 Pg C year-1. As dryland soils have high inorganic C contents compared to organic C, mechanisms of the nocturnal CO2 uptake likely involve both biotic and abiotic processes that are tightly coupled to water availability. Biological soil crusts (hereafter, biocrusts) cover about 30% of global drylands and provide favourable physico-chemical hotspots for this C exchange mechanism. In this study, we present a mechanistic model of inorganic C binding that is enhanced by the activity of biocrust communities. The model results show good agreement with field measurements of the soil-atmosphere CO2 exchange dynamics under contrasting conditions of water availability and temperature in the Tabernas Desert (Spain). We further show that inorganic C sequestration rates at night vary, depending on the successional stages of biocrusts. Our findings have the potential to substantially improve the often-overlooked processes of dryland systems in the global C cycle. By unravelling the mechanisms occurring along the succession of biocrusts, this study highlights the roles of soil biological agents in mitigating CO2 emissions in a drier future.

In dryland landscapes, patches of vascular plants can respond to environmental stress by adjusting their spatial pattern to intercept runoff more effectively, i.e., spatially self-organize, and maintain productivity. However, vegetation patch dynamics in drylands often assumes interspaces of plant patches are composed only of bare soil. Biological soil crusts (BSCs) are complex communities, largely of cyanobacteria, algae, lichens, and bryophytes, living in the soil surface in drylands and often cover more area than vascular plants. BSCs often occur in patches of light cyanobacteria and dark-mixed aggregates and can significantly affect and respond to ecohydrological feedbacks in dryland ecosystems. However, little is known about their spatial patterns and dynamics. In this study, we investigate spatial attributes of BSC patches, their spatial interactions with vascular plants, and factors that drive variation in these attributes. We collected ultra-high-resolution (1-cm) data on spatial patterns of BSCs and vascular plants at 26 sites across three ecoregions of the Southwest of the United States of America. Our analysis shows that light cyanobacterial BSCs vary most in their patch shape complexity along the aridity gradient, while dark-mixed BSCs vary strongly in their abundance. The abundance of dark-mixed BSCs is significantly affected by the soil template, namely soil texture and calcareousness, as well as vascular plants to persist under stress. Furthermore, species associations also change with environmental stress. Light cyanobacteria BSCs, likely a significant source of runoff, may act as a buffer for woody plants against drying, as spatial interactions between these biota become more positive (i.e., spatially aggregated) with greater aridity. While dark-mixed BSCs rely significantly on soil conditions and reduce in abundance as a response to aridity stress, we find evidence that they may have some capacity to spatially adjust under conditions of constant aridity. The interaction of dark-mixed BSCs with light cyanobacteria patches becomes more positive with slope. We conclude that light cyanobacteria BSCs can likely change patch shape in response to water limitation, while dark-mixed BSCs have a reduced capacity to do so – providing further evidence that the abundance of dark-mixed BSCs will decline in the future under drying. BSCs and vascular plants coordinate in space in response to resource availability, suggesting the need to consider self-organization of multiple assemblages to fully understand dryland response to climatic change.

Nitrous acid (HONO) is an important component of the nitrogen cycle in the atmosphere. Photolysis of HONO generates hydroxyl (OH) radicals and significantly influences the atmospheric oxidative capacity. Early laboratory work discovered that soil nitrite, produced via biological nitrification or denitrification, can be an important HONO source. However, the laboratory-determined chamber HONO fluxes can largely deviate from those in the real world for the same soil sample. Therefore, quantification of soil fluxes of HONO in the atmosphere remains challenging. [HONO]*, the equilibrium gas-phase concentration over the aqueous solution of nitrous acid in the soil, has been suggested as a key parameter for quantifying soil fluxes of HONO; but it has not yet been well-validated and quantified. In this project, we present a method to retrieve [HONO]* by conducting controlled dynamic chamber experiments with soil samples and validate the existence of [HONO]* over the soil. We show that [HONO]* is a soil characteristic, independent of HONO concentrations in the chamber. Therefore, it is reliable to use [HONO]* to quantify soil fluxes of HONO. [HONO]* performs as an indicator of the potential of soil to be a source or a sink for atmospheric HONO and helps to better quantify the role of HONO fluxes of soil in the HONO budget and its implications on the oxidizing capacity in the atmosphere.

Nonvascular photoautotrophs (NVP), including bryophytes, lichens, terrestrial algae, and cyanobacteria, are increasingly recognized as being essential to ecosystem functioning in many regions of the world. Current research suggests that climate change may pose a substantial threat to NVP, but the extent to which this will affect the associated ecosystem functions and services is highly uncertain. Here, we propose a research agenda to address this urgent question, focusing on physiological and ecological processes that link NVP to ecosystem functions while also taking into account the substantial taxonomic diversity across multiple ecosystem types. Accordingly, we developed a new categorization scheme, based on microclimatic gradients, which simplifies the high physiological and morphological diversity of NVP and world-wide distribution with respect to several broad habitat types. We found that habitat-specific ecosystem functions of NVP will likely be substantially affected by climate change, and more quantitative process understanding is required on (1) potential for acclimation, (2) response to elevated CO2, (3) role of the microbiome, and (4) feedback to (micro)climate. We suggest an integrative approach of innovative, multimethod laboratory and field experiments and ecophysiological modelling, for which sustained scientific collaboration on NVP research will be essential.

Biocrusts are a worldwide phenomenon, contributing substantially to ecosystem functioning. Their growth and survival depend on multiple environmental factors, including climatic conditions. While the physiological responses of biocrusts to individual environmental factors have been examined in laboratory experiments, the relative importance of these factors along climatic gradients is largely unknown. Moreover, it is not fully understood how acclimation of biocrusts may alter the relative impacts of certain factors. We aim here at determining the relative effects of environmental factors on biocrusts along climatic gradients, using the carbon balance of biocrust organisms as a measure of their performance. Additionally, we explore the role that seasonal acclimation plays in the carbon balance of biocrusts. We applied a data-driven mechanistic model at six study sites along a climatic gradient to simulate the annual carbon balance of biocrusts dominated by different lichen and moss species. Furthermore, we performed several sensitivity analyses to investigate the relative importance of driving factors, thereby including the impacts of acclimation. Our modeling approach suggests substantial effects of light intensity and relative humidity in temperate regions, while air temperature has the strongest impact at alpine sites. In drylands, ambient CO2 concentration and also the amount of rainfall are important drivers of the carbon balance of biocrusts. Seasonal acclimation is a key feature, mostly in temperate regions, affecting biocrust functioning. We conclude that climate change, which may lead to warmer and, in some regions, drier air, will potentially have large effects on long-term carbon balances of biocrusts at global scale. Moreover, we highlight the key role of seasonal acclimation, which suggests that the season and timing of collecting and monitoring biocrusts should be given additional consideration in experimental investigations, especially when measurements are used as the basis for quantitative estimates and forecasts.

Resumen Introduccion El cateterismo de senos petrosos inferiores (CSPI) esta indicado en el diagnostico de sindrome de Cushing (SC) hormona adrenocorticotropa (ACTH) dependiente, especialmente cuando los resultados del resto de las pruebas diagnosticas son discordantes. Objetivo Describir los pacientes a quienes se les realizo esta prueba invasiva funcional en un hospital de tercer nivel. Metodos Estudio observacional sobre una cohorte retrospectiva de pacientes con SC ACTH-dependiente y CSPI entre los anos 2004 y 2019. Se determinaron sus caracteristicas epidemiologicas, hormonales, radiologicas y funcionales, evaluandose su capacidad diagnostica y puntos de corte optimos para diferenciar entre enfermedad de Cushing (EC) y sindrome de Cushing ectopico (SCE). Resultados Fueron evaluados 23 pacientes de los cuales 65,2% fueron mujeres y la edad promedio fue 42 (36-62) anos. Se evidencio una secrecion de ACTH de origen hipofisario en el 82,6% de los pacientes y de origen ectopico en el 17,4%. Los niveles de cortisol plasmatico, cortisol libre urinario y ACTH fueron mas elevados en pacientes con SCE. Respecto al CSPI, el gradiente ACTH central/periferico (C/P) basal detecto el 89,5% de pacientes con EC y tras estimulacion con de la hormona liberadora de corticotropina (CRH) el 100%, siendo los puntos de corte optimos para el diagnostico de EC 2,06 basal y 2,49 tras estimulacion con CRH. Conclusiones El CSPI con estimulacion de CRH es una prueba con alta precision diagnostica para clasificar de manera correcta a los pacientes con EC y SCE. Los puntos de corte de los gradientes pueden ser distintos a los valores clasicos, por lo que recomendamos que cada centro los evalue.

Biocrusts covering drylands account for major fractions of terrestrial biological nitrogen fixation and release large amounts of gaseous reactive nitrogen (Nr) as nitrous acid (HONO) and nitric oxide (NO). Recent investigations suggested that aerobic and anaerobic microbial nitrogen transformations occur simultaneously upon desiccation of biocrusts, but the spatio-temporal distribution of seemingly contradictory processes remained unclear. Here, we explore small-scale gradients in chemical concentrations related to structural characteristics and organism distribution. X-ray microtomography and fluorescence microscopy revealed mixed pore size structures, where photoautotrophs and cyanobacterial polysaccharides clustered irregularly in the uppermost millimeter. Microsensor measurements showed strong gradients of pH, oxygen, and nitrite, nitrate, and ammonium ion concentrations at micrometer scales in both vertical and lateral directions. Initial oxygen saturation was mostly low (∼30%) at full water holding capacity, suggesting widely anoxic conditions, and increased rapidly upon desiccation. Nitrite concentrations (∼6 to 800 μM) and pH values (∼6.5 to 9.5) were highest around 70% WHC. During further desiccation they decreased, while emissions of HONO and NO increased, reaching maximum values around 20% WHC. Our results illustrate simultaneous, spatially separated aerobic and anaerobic nitrogen transformations, which are critical for Nr emissions, but might be impacted by future global change and land management.

Biological soil crusts (abbreviated as biocrusts) are composed of photoautotrophic cyanobacteria, algae, lichens, and bryophytes, growing together with heterotrophic bacteria, archaea and fungi and forming an intimate association with soil particles in the uppermost millimeters of the substrate. They occur globally in drylands, where they cover about 1/3 of the soil surface, corresponding to an area of about 18 x 106 km2. Biocrusts fix atmospheric nitrogen (N), which is needed for physiological processes and the formation of biomass. However, it recently was also shown that similar to bulk soil, N is cycled within biocrusts and major fractions of it are released as nitrous acid (HONO) and nitric oxide (NO) to the atmosphere.Based on these initial results, we investigated the biologically mediated N-cycling processes in biocrusts as related to wetting and drying events. We investigated the microbial activity at different drying stages by means of transcriptome analysis and related these results to soil nitrite and nitrate concentrations over time. In addition, we utilized catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) to quantify the number of bacteria, archaea, and nitrite oxidizing bacteria in different strata over time.Our results revealed that within less than 30 minutes after wetting, genes encoding for all relevant N cycling processes, including N fixation, ammonification, nitrification, denitrification, and assimilatory and dissimilatory N reduction were expressed. The most abundant transcriptionally active N-transforming microorganisms belonged to the Rhodobacteraceae, Enterobacteriaceae and Pseudomonadaceae within the Alpha- and Gammaproteobacteria. The soil nitrite contents increased significantly during the desiccation process, likely serving as a precursor for NO and HONO emissions, which peaked at relatively low water contents of ~20% water holding capacity. This nitrite accumulation was likely caused by a differential expression of nitrite as compared to nitrate reductase encoding genes over the course of desiccation. Additionally, our data suggest that ammonia-oxidizing organisms may have responded to changing local oxygen conditions during drying. These mechanisms are also supported by process-based modelling, which has been conducted by us. Thus, our results show that the activity of N-cycling microorganisms, as related to the water and oxygen conditions within the substrate, determines the process rates and overall quantity of reactive nitrogen emissions.

The vegetation and soils of the Amazon contain large amounts of carbon that may be vulnerable to loss given ongoing climate and land use change in the Amazon basin. Previous studies predicted that the Amazon rainforest would start to act as a net carbon source to the atmosphere by 2030-2040, and that it has switched from being a sink to source over the last decade. Using data from eddy covariance and vertical carbon dioxide profile measurement systems installed at the 80 m walk-up tower in the Amazon Tall Tower Observatory (ATTO) site, located in well-preserved central Amazon upland rainforest, we assessed net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco) for the period 2014-2019. The NEE results indicate that the central Amazon upland rainforest was carbon neutral or a source during this 6-year period. Seasonal GPP variations were related to soil water availability and vapor pressure deficit. The strong 2015-2016 El Niño event decreased both GPP and Reco due to the unusually long dry period, but also contributed to carbon flux dynamics in post El Niño periods. In the 2017-dry season, we measured higher dry-season GPP compared with the other years, which we hypothesize was triggered by photosynthesis activation in sub-canopy and understory trees. This is supported by the minimum green crown fraction at upper canopy trees, indicating more light availability in lower canopy trees, and the higher fraction of absorbed photosynthetically active radiation, both recorded during the dry-season of 2017. Our results show that the ground-based measurement setup at ATTO is well suited to investigate the local carbon fluxes on seasonal to interannual time scales.

Biocrusts are distributed over all climate zones of the world and they substantially contribute to ecosystem functioning. Their growth, determined by their carbon balance, can be affected by various climatic drivers. The effects of individual drivers are clear from laboratory experiments, but the relative importance of different drivers along climatic gradients and their underlying mechanisms are largely unknown. Moreover, the effects of seasonal acclimation on the annual carbon balance are not fully understood either. Therefore, we aim at determining the level and variation of annual biocrust carbon balances and their connection to climatic drivers along environmental gradients. In addition, we explore the role that acclimation plays in the carbon balance of biocrusts.Here, we applied a data-driven model at six study sites along climate gradients and performed several sensitivity analyses to investigate the most relevant factors for the annual carbon balance, including impacts of acclimation of traits. The model was developed using a physiology-based photosynthesis model, and the necessary parameters were obtained from field and laboratory measurements.We found a consistent set of control factors under different climate conditions, namely radiation, relative humidity, surface temperature, and ambient CO2 concentration, which were of roughly equal relevance. However, the effect of relative humidity on the carbon balance depended on the habitat’s microclimate, and a reduction in non-rainfall water sources resulted in more carbon loss in drylands but fostered carbon gain in humid environments. In addition to climate factors, the seasonal acclimation of traits played an essential role in the annual carbon balance at humid sites. Thereby, not accounting for acclimation processes in models of biocrusts may be a potential explanation for estimated negative carbon balances in humid regions.Our results suggest that global change, which may lead to warmer and drier air in some regions, will likely affect biocrust long-term carbon balances. Moreover, for experimental investigations, the season and timing of collecting and monitoring the species should be given additional consideration, especially when the traits are used as the basis for quantitative estimates and forecasts.

The capture and use of water are critically important in drylands, which collectively constitute Earth's largest biome. Drylands will likely experience lower and more unreliable rainfall as climatic conditions change over the next century. Dryland soils support a rich community of microphytic organisms (biocrusts), which are critically important because they regulate the delivery and retention of water. Yet despite their hydrological significance, a global synthesis of their effects on hydrology is lacking. We synthesized 2,997 observations from 109 publications to explore how biocrusts affected five hydrological processes (times to ponding and runoff, early [sorptivity] and final [infiltration] stages of water flow into soil, and the rate or volume of runoff) and two hydrological outcomes (moisture storage, sediment production). We found that increasing biocrust cover reduced the time for water to pond on the surface (−40%) and commence runoff (−33%), and reduced infiltration (−34%) and sediment production (−68%). Greater biocrust cover had no significant effect on sorptivity or runoff rate/amount, but increased moisture storage (+14%). Infiltration declined most (−56%) at fine scales, and moisture storage was greatest (+36%) at large scales. Effects of biocrust type (cyanobacteria, lichen, moss, mixed), soil texture (sand, loam, clay), and climatic zone (arid, semiarid, dry subhumid) were nuanced. Our synthesis provides novel insights into the magnitude, processes, and contexts of biocrust effects in drylands. This information is critical to improve our capacity to manage dwindling dryland water supplies as Earth becomes hotter and drier. This work was conducted as part of the Powell Working Group “Completing the dryland puzzle: creating a predictive framework for biological soil crust function and response to climate change” supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the US Geological Survey. J.B. and S.R. were funded by USGS Ecosystems and Land Use Change Mission Areas, by the US Department of Energy (DESC-0008168), and by the Strategic Environmental Research and Development Program (RC18-1322). J.D. is supported by grants from the Holsworth Wildlife Research Endowment & The Ecological Society of Australia, and a scholarship from China Scholarship Council (No. 201706040073). B.C. is supported by grants from the National Science Foundation (award DEB-1844531) and DePaul University. M.A.B. is supported by a grant from the National Science Foundation (award DEB-1638966). B.W. was supported by the Max Planck Society and a Paul Crutzen Nobel Laureate Fellowship. E.H.-S. was supported by CONACYT grant 251388 B. F.T.M. was supported by the European Research Council (ERC grant agreement 647038 [BIODESERT]) and Generalitat Valenciana (CIDEGENT/2018/041).

Studies of biological soil crusts (biocrusts) have proliferated over the last few decades. The biocrust literature has broadened, with more studies assessing and describing the function of a variety of biocrust communities in a broad range of biomes and habitats and across a large spectrum of disciplines, and also by the incorporation of biocrusts into global perspectives and biogeochemical models. As the number of biocrust researchers increases, along with the scope of soil communities defined as ‘biocrust’, it is worth asking whether we all share a clear, universal, and fully articulated definition of what constitutes a biocrust. In this review, we synthesize the literature with the views of new and experienced biocrust researchers, to provide a refined and fully elaborated definition of biocrusts. In doing so, we illustrate the ecological relevance and ecosystem services provided by them. We demonstrate that biocrusts are defined by four distinct elements: physical structure, functional characteristics, habitat, and taxonomic composition. We describe outgroups, which have some, but not all, of the characteristics necessary to be fully consistent with our definition and thus would not be considered biocrusts. We also summarize the wide variety of different types of communities that fall under our definition of biocrusts, in the process of highlighting their global distribution. Finally, we suggest the universal use of the Belnap, Büdel & Lange definition, with minor modifications: Biological soil crusts (biocrusts) result from an intimate association between soil particles and differing proportions of photoautotrophic (e.g. cyanobacteria, algae, lichens, bryophytes) and heterotrophic (e.g. bacteria, fungi, archaea) organisms, which live within, or immediately on top of, the uppermost millimetres of soil. Soil particles are aggregated through the presence and activity of these often extremotolerant biota that desiccate regularly, and the resultant living crust covers the surface of the ground as a coherent layer. With this detailed definition of biocrusts, illustrating their ecological functions and widespread distribution, we hope to stimulate interest in biocrust research and inform various stakeholders (e.g. land managers, land users) on their overall importance to ecosystem and Earth system functioning. This work was conducted as part of the “Completing the dryland puzzle: creating a predictive framework for biological soil crust function and response to climate change” Working Group supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the U.S. Geological Survey. V.B.C. is funded by the National Science Foundation (DEB-1844531). F.T.M. acknowledges support from the European Research Council (ERC Grant Agreement 647038 [BIODESERT]) and Generalitat Valenciana (CIDEGENT/2018/041). K.E.Y. and A.D.-N. were supported by the National Science Foundation (#1557162 & #1557135). E.R.-C. was supported by the Ramon y Cajal fellowship (RYC2020-030762-I) and the REBIOARID Project (2018-101921-B-I00) founded by FEDER/Ministerio de Ciencia e Inovacion-Agencia estatal de investigacion, and the BIOCOST project (Conservación debiocostras como estrategia de adaptación al cambio climático: alineando avances científicos con la gestión y sociedad) supported by the Biodiversity Foundation of the Ministry for the Ecological Transition and the Demographic Challenge. S.C.R. was supported by USGS Ecosystems Mission Area. E.H.-S. acknowledges financial support from CONACYT grant SEP-CB-2015-01-251388.

X ray microspectroscopy is a powerful analytical method in geoscientific and environmental research as it provides a unique combination of nanoscale imaging with high spectroscopic sensitivity at relatively low beam related sample damage. In this study, classical scanning transmission soft X ray microscopy STXM with X ray absorption spectroscopy and the recently established soft X ray ptychography are applied to the analysis of selected rock varnish samples from urban and arid desert environments. X ray ptychography enhances the spatial resolution relative to STXM by up to 1 order of magnitude. With its high chemical sensitivity, it can resolve nanoscale differences in valence states of the key varnish elements manganese Mn and iron. Our results emphasize the complex nanoarchitecture of rock varnish as well as the diverse mineralogy of the Mn oxy hydroxide matrix and its embedded dust grains. In contrast to the fast growing urban varnish, the slow growing arid desert varnish revealed a remarkable nanoscale stratification of alternating Mn valence states, providing hints on the layer wise and still enigmatic growth process

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.

Dryland ecosystems usually show low productivity, considerable water losses and land degradation problems associated with soil erosion. Most bare-looking areas in these ecosystems are covered by biocrusts, which represent an important nitrogen and carbon sink and provide essential ecosystem services. However, until now no studies analyzed the role of biocrusts in providing ecosystem services and compared these with the societal perception of biocrust-dominated ecosystems. In this study, we quantified the direct effect of biocrusts on soil water regulation, erosion control and climate and air quality in two different semiarid ecosystems dominated by biocrusts, and we explored the social importance and perceived vulnerability regarding the capacity of these ecosystems to provide services to society. Our results disclose an important role of biocrusts in providing four services, with indirect implications on other important ecosystem functions. However, interview partners neither recognized the capacity of the two analyzed ecosystems to provide supporting services nor their social importance. Survey respondents mostly valued provisioning services related to extraction activities, such as agriculture, which produce direct economic income but conversely threat biocrust sustainability. Thus, more effort is needed by scientists and policy makers to raise awareness on the key role of drylands with biocrust communities in preserving ecosystem functions that directly provide regulating services. Moreover, their protection is demanded not only for the provision of key ecosystem services, but also because biocrusts themselves should be considered as communities valued by humans.

Biological soil crusts (biocrusts) release the reactive nitrogen gases (Nr) nitrous acid (HONO) and nitric oxide (NO) into the atmosphere, but the underlying microbial process controls have not yet been resolved. In this study, we analyzed the activity of microbial consortia relevant in Nr emissions during desiccation using transcriptome and proteome profiling and fluorescence in situ hybridization. We observed that < 30 min after wetting, genes encoding for all relevant nitrogen (N) cycling processes were expressed. The most abundant transcriptionally active N-transforming microorganisms in the investigated biocrusts were affiliated with Rhodobacteraceae, Enterobacteriaceae, and Pseudomonadaceae within the Alpha- and Gammaproteobacteria. Upon desiccation, the nitrite (NO2−) content of the biocrusts increased significantly, which was not the case when microbial activity was inhibited. Our results confirm that NO2− is the key precursor for biocrust emissions of HONO and NO. This NO2− accumulation likely involves two processes related to the transition from oxygen-limited to oxic conditions in the course of desiccation: (i) a differential regulation of the expression of denitrification genes; and (ii) a physiological response of ammonia-oxidizing organisms to changing oxygen conditions. Thus, our findings suggest that the activity of N-cycling microorganisms determines the process rates and overall quantity of Nr emissions.

Biological soil crusts (referred to as biocrusts hereafter) represent communities comprising a fraction of photoautotrophs (photoautotrophic bacteria, algae, lichens, and bryophytes) growing together with heterotrophic organisms like bacteria, archaea, and fungi. The organisms are all poikilohydric, which means they are only active if water is present. They occur frequently in dryland ecosystems, where vascular vegetation is sparse or even absent, or wherever dry microclimatic conditions occur. Biocrusts fulfill a wide range of important ecosystem services, as they are relevant in regional water cycling, soil stabilization, plant germination and growth, and also global carbon (C) and nitrogen (N) cycling. According to initial estimates, they are supposed to globally emit ~1.7 Tg of reactive nitrogen (Nr) per year, corresponding to ~20% of the global nitrogen oxide emissions from soils under natural vegetation. The underlying mechanisms of Nr emissions in biocrusts, however, are not well understood and are still a focus of ongoing research.This study aimed to explore the functional roles of microbial organisms in Nr emissions along a full wetting and drying cycle. Therefore, Nr fluxes were analyzed at three key hydration stages, i.e., immediately after wetting (T1), prior to (T2), and after maximum Nr fluxes (T3). At all three stages, the transcriptome (microarray analysis) and proteome (metaproteomics) were profiled to highlight changes in biological processes linked to nitrogen transformation. Additionally, at T1 and T2, the bacterial, archaeal, and nitrite-oxidizing bacterial communities were quantified utilizing catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH). Soil nitrite and nitrate contents of both intact and sterilized biocrust samples were analyzed before and after a measurement cycle.Our results showed a fast recovery of microbial activity minutes after wetting of the biocrusts (T1) by means of mRNA expression of nitrogen transformative genes. Transcripts of genes encoding all major N-cycling processes that are already known from soil were detected. The number of N-transforming species and processes detected by the microarray analysis significantly increased from T1 to T2 to T3. The most prominent nitrogen transforming microorganisms belonged to Alpha- and Gammaproteobacteria. The CARD-FISH data showed a significant increase in archaeal numbers from T1 to T2, which is in line with an observed increase in Nr emissions. The majority of identified proteins were related to ATP synthesis, photosynthesis, protein biosynthesis and stress response, whereas proteins assigned to N transformation could not be observed. Soil N-content analysis showed a significant increase of nitrite in living biocrusts after a wetting and drying cycle, which was likely promoted by nitrifying Archaea and Proteobacteria, but also by various denitrifying bacteria, as suggested by microarray analysis and CARD-FISH. This indicates that Nr fluxes largely originated from nitrite formed by various aerobic and anaerobic biotic processes, likely occurring simultaneously in different microhabitats within the biocrust.

Primary biological aerosol particles (PBAP), better known as bioaerosols, are considered to play a role in atmospheric and climate influencing processes. Fungal spores, as a part of PBAP, account for a large fraction of coarse particulate matter in some ecosystems, as for example the Amazon rainforest. In such highly diverse ecosystems, fungi play key roles as mycorrhizal fungi for nutrient uptake of plants and as decomposers in nutrient and water cycling, and thus their community structure strongly influences local ecosystem conditions. Despite this relevance, fungal spore emission patterns under natural conditions and the corresponding triggering factors are not well characterized, yet. In this study, we present a laboratory and field measurement techniques to quantify and analyze bioaerosol emission patterns and the effect of precipitation on fungal spore emission.For investigations under field conditions, the particle emissions of fungi (Agaricomycetes) were characterized at their site of growth in the field using an optical particle sizer and a data logger. Particle concentrations and their size distribution (0.3 to 10 µm), as well as the microclimatic temperature and humidity were measured in close vicinity to the fungal fruiting body. Generally, field measurements were performed over a time span of 24 h with some exceptions ranging up to 6 days. For laboratory measurements, a newly developed glass chamber system was used to measure particle emissions of fungi under controlled conditions. During the chamber measurements, the humidity and temperature conditions were varied and recorded with a datalogger. To simulate precipitation events, the fruiting bodies were sprayed with water between measurement sections and particle emissions were monitored before and after moistening.First measurements of fungi under field and lab conditions showed that high humidity values were necessary to trigger fungal spore emissions. In many cases, precipitation events and the moisture status of the fungus and substrate had an influence on spore release. Based on the results of 47 field measurements, it was possible to establish a function simulating the spore emission patterns of fungi during their diurnal emission cycle. During field measurements, an emission of up to 55,000 spores per second was recorded directly at the fungus, which, according to the function, may correspond to emissions of up to 2.8 x 109 spores per day. Chamber measurements showed that spore emissions generally started 2-3 hours after artificial moistening.Increasing deforestation is expected to cause drier conditions and to increase the possibility of droughts, which will have an impact on the species composition and quantity of fungi in the Amazon. A combination of our field and lab emission data is expected to allow a new interpretation of bioaerosol emissions and composition in the Amazon, which can be used as a baseline to analyze the potential relevance of bioaerosols in regional atmosphere and climate processes.

Biological soil crusts (biocrusts) are a complex community of algae, cyanobacteria, lichens, bryophytes, and assorted bacteria, fungi, archaea, and bacteriophages that colonize the soil surface. Biocrusts are particularly common in drylands and are found in arid and semiarid ecosystems worldwide. While diminutive in size, biocrusts often cover large terrestrial areas, provide numerous ecosystem benefits, enhance biodiversity, and are found in multiple configurations and assemblages across different climate and disturbance regimes. Biocrusts have been a focus of many ecologists, especially those working in semiarid and arid lands, as biocrusts are foundational community members, play fundamental roles in ecosystem processes, and offer rare opportunities to study biological interactions at small and large spatial scales. Due to these same characteristics, biocrusts have the potential to serve as an excellent teaching tool. The purpose of this paper is to demonstrate the utility of biocrust communities as a model system in science education. Functioning as portable, dynamic mini ecosystems, biocrusts can be used to teach about organisms, biodiversity, biotic interactions, abiotic controls, ecosystem processes, and even global change, and can be easy to use in nearly every classroom setup. For example, education principles, such as evolution and adaptation to stress, or structure and function (patterns and processes) can be applied by bringing biocrusts into the classroom as a teaching tool. In addition, discussing the utility of biocrusts in the classroom – including theory, hypothesis testing, experimentation, and hands-on learning – this document also provides tips and resources for developing education tools and activities geared toward impactful learning.

To resolve the various types of biological ice nuclei (IN) with atmospheric models, an extension of the empirical parameterization (EP) (Phillips et al. 2008; 2013) is proposed to predict the active IN from multiple groups of primary biological aerosol particles (PBAPs). Our approach is to utilize coincident observations of PBAP sizes, concentrations, biological composition, and ice-nucleating ability. The parameterization organizes the PBAPs into five basic groups: fungal spores, bacteria, pollen, viral particles, plant/animal detritus, algae, and their respective fragments. This new biological component of the EP was constructed by fitting predicted concentrations of PBAP IN to those observed at the Amazon Tall Tower Observatory (ATTO) site located in the central Amazon. The fitting parameters for pollen and viral particles, plant/animal detritus, which are much less active as IN than fungal and bacterial groups, are constrained based on their ice nucleation activity from the literature. The parameterization has empirically derived dependencies on the surface area of each group (except algae), and the effects of variability in their mean sizes and number concentrations are represented via their influences on the surface area. The concentration of active algal IN is estimated from literature-based measurements.Predictions of this new biological component of the EP are consistent with previous laboratory and field observations not used in its construction. The EP scheme was implemented in a 0D parcel model. It confirms that biological IN account for most of the total IN activation at temperatures warmer than −20°C and at colder temperatures dust and soot become increasingly more important to ice nucleation.

Background Inferior petrosal sinus sampling (IPSS) is indicated in the diagnosis of adrenocorticotropic hormone (ACTH)-dependent Cushing's syndrome (CS), especially when the results of the initial diagnostic tests are discordant. Objective To describe the patients who underwent this invasive functional test in a tertiary hospital. Methods This was an observational study of a retrospective cohort of patients with ACTH-dependent CS and IPSS between 2004 and 2019. We determined their epidemiological, hormonal, radiological and functional characteristics, and evaluated their diagnostic capacity and optimal cut-off points to differentiate between Cushing's disease (CD) and ectopic Cushing's syndrome (ECS). Results 23 patients were evaluated, of which 65.2% were women with the average age of 42 (36–62) years. ACTH secretion of pituitary origin was evident in 82.6% of the patients and of ectopic origin in 17.4%. Plasma cortisol, urinary free cortisol, and ACTH levels were higher in patients with ECS. Regarding IPSS, the baseline central/peripheral ACTH gradient detected 89.5% of patients with CD and after stimulation with CRH, 100%. The optimal cut-off points in the diagnosis of CD were 2.06 at baseline and 2.49 after CRH stimulation. Conclusion IPSS with CRH stimulation is a test with a high diagnostic accuracy for correctly classifying patients with CD and ECS. The cut-off points of the gradients may be different from the classic ones. Therefore, we recommend that each center perform its own evaluation.

The uncompetitive N-methyl-D-aspartate (NMDA) receptor (NMDAR) antagonist ketamine has been proposed to model symptoms of psychosis. Inhibitory deficits in the schizophrenia spectrum have been reliably reported using the antisaccade task. Interestingly, although similar antisaccade deficits have been reported following ketamine in non-human primates, ketamine-induced deficits have not been observed in healthy human volunteers. To investigate the effects of ketamine on brain function during an antisaccade task, we conducted a double-blind, placebo-controlled, within-subjects study on n = 15 healthy males. We measured the blood oxygen level dependent (BOLD) response and eye movements during a mixed antisaccade/prosaccade task while participants received a subanesthetic dose of intravenous ketamine (target plasma level 100 ng/ml) on one occasion and placebo on the other occasion. While ketamine significantly increased self-ratings of psychosis-like experiences, it did not induce antisaccade or prosaccade performance deficits. At the level of BOLD, we observed an interaction between treatment and task condition in somatosensory cortex, suggesting recruitment of additional neural resources in the antisaccade condition under NMDAR blockage. Given the robust evidence of antisaccade deficits in schizophrenia spectrum populations, the current findings suggest that ketamine may not mimic all features of psychosis at the dose used in this study. Our findings underline the importance of a more detailed research to further understand and define effects of NMDAR hypofunction on human brain function and behavior, with a view to applying ketamine administration as a model system of psychosis. Future studies with varying doses will be of importance in this context.