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Vegetation restoration often promotes the development of biological soil crusts (biocrusts), which have a significant role in the terrestrial nitrogen (N) cycle. However, biocrusts are not always considered when assessing soil N responses to restoration efforts, especially in subtropical regions. We assessed the effect of various restoration strategies on moss-dominated biocrust properties and soil N variables (0–5 cm topsoil and 5–10 cm sub-topsoil) in the subtropical karst region of southwestern China. Four restoration strategies were included: restoration with plantation forest, forage grass, and a combination of forest and grass, and spontaneous regeneration to natural grassland. Cropland under maize-soybean rotation (CR) was used as reference. The biocrust under combination restoration strategy had significantly higher biomass, saturated water adsorption ratio, and carbon content than did the other strategies; and the soil generally had the highest total N, ammonium, and microbial biomass carbon and N content but the lowest nitrate content. Redundancy analysis, variation partitioning, and stepwise multiple linear regression all indicated that biocrust properties play an important role in affecting soil N variables, especially in the topsoil. Vegetation restoration strategies that use various plant functional group assemblages, such as forest and grass, are preferable in enhancing the development of biocrusts and thus improving soil N properties. • Vegetation restoration is beneficial in promoting biocrust development. • Biocrust properties were the main factors affecting soil N variations. • Combination of plantation trees and forage grasses had higher soil N and biocrusts. • Combination restoration strategy should be favored in vegetation restoration efforts. [ABSTRACT FROM AUTHOR]

Abstract Little is known about phosphorus (P) in biological soil crusts (BSCs) and their role in biogeochemical P cycling. The present study evaluated P in BSCs with an array of methodological approaches including sequential P fractionation, solution 31P nuclear magnetic resonance (NMR) spectroscopy, synchrotron-based P K -edge X-ray absorption near-edge structure (XANES) spectroscopy, elemental mapping (μ-XRF) combined with μ-XANES and P-lipid quantification. BSCs (light algal crusts) were collected at seven sites along a sediment weathering gradient in north-eastern Germany (based on feldspar weathering indices) from non-weathered dune sands at the Baltic Sea coast to more strongly weathered Weichselian glacio-fluvial sands near Berlin. The total P (P t) concentrations of BSCs ranged from 93 to 389 mg kg−1 and were not significantly correlated with the change in feldspar weathering index. While concentrations of stable P (H 2 SO 4 -extractable) strongly decreased, labile P (resin- + NaHCO 3 -extractable P) in BSCs increased with increasing sediment weathering. Based on 31P NMR spectra, 20 to 62% of NaOH-EDTA extracted P was orthophosphate monoesters and 0 to 9% was diesters. For BSCs, P K -edge XANES showed that Ca-P species decreased with increasing weathering. Heterogeneity of the BSCs was exemplarily shown at the micrometre scale by element mapping μ-XRF and μ-XANES, using four 10 × 10 μm spots of a vertical cross-section within a coastal dune BSC. While only the P-lipid class phosphatidic acid (PA) increased with increasing weathering, analyses of BSC phospholipid fatty acids (PLFAs) revealed decreasing contributions of Gram-positive bacteria with increasing coastal sediment weathering but different taxa were independent of any investigated P parameter. Proportions of lipid-P varied between 0.02 and 0.1% of P t , indicating a constant share of living biomass in BSCs along the gradient. In conclusion, this multi-method study of P speciation in BSCs showed that these communities play a key role in the biogeochemical P cycle, especially by transforming stable P into labile, easily bioavailable P. Graphical abstract Unlabelled Image Highlights • Stable and labile P of BSCs were affected by sediment weathering state. • BSC lipid-P and most phospholipid classes were not affected by weathering state. • The weathering stage determined the BSC community structure. • P-speciation of a coastal dune BSC varied on μm-scale. • BSC communities play a biogeochemical key role in the P cycle. [ABSTRACT FROM AUTHOR]

• SP performed better for vicarious calibration than the traditional protocol. • SP enables predicting hydrophobicity levels over undisturbed soil surfaces. • SP preserves soil seal and better predicts water infiltration rate into soil. • SP extracts surface reflectance properties under critical outdoor conditions. The SoilPRO® (SP) is an assembly designed to acquire soil reflectance information in the field without disturbing the soil surface, and regardless of atmospheric and solar radiation conditions. This paper summarizes five case studies in which the SP assembly was used for different applications. The case studies consisted of: (1) generating surface spectral measurements under any atmospheric condition; (2) comparing the performance of the SP to the traditional bare fiber method for vicarious calibration of hyperspectral satellite sensors; (3) assessing water repellency of a soil surface governed by organic matter hydrophobicity; (4) spatial prediction of the rate of water infiltration into the soil profile as governed by the soil surface seal; and (5) using the SP apparatus to measure soil surface reflectance in South Shetland Island, Antartica under severe weather conditions. The case studies included calculation of spectral quality, prediction accuracy and measurement stability. The paper discusses each of the cases in detail and concludes that the SP (or similar assembly) is the best way to measure the reflectance of the original soil surface in the field. In the first case study, the spectrum collected by the SP under daily changing illumination was shown to be stable relative to the traditional measurement methods of contact probe or bare fiber. The second case study indicated that use of the SP for vicarious calibration is much more efficient (in terms of time and stability) than ground-truth practice over a large area, and in the third case study, the SP was able to assess a soil surface property governed by organic matter hydrophobicity better than the contact probe, which destroys the soil surface organic seal. A similar achievement was gained in the fourth case study, providing a better assessment of the water-infiltration rate into the soil. In the fifth case study, the SP demonstrated impressive high-quality acquisition of soil surface reflectance with a very low sun angle over the South Pole. Based on these case studies and the high quality of the data generated by the SP in the field, we suggest building, in parallel to the classical soil spectral libraries generated in the laboratory, field soil spectral libraries that will preserve the soil surface properties scanned in the field. We anticipate the development of more applications for the SP assembly based on the capabilities shown in this paper. [ABSTRACT FROM AUTHOR]

The estimation of saturated hydraulic conductivity (Ks) is of high relevance to correctly reproduce water fluxes, such as infiltration rates or surface runoff in hydrological simulations. Yet, estimation of Ks is challenging especially in semi-arid regions with particular soil surface characteristics like crusting and sealing. This study presents results of a field campaign in the semi-arid Walnut Gulch Experimental Watershed, Arizona (US), where surface and subsurface Ks measurements were undertaken across the watershed. Data of saturated hydraulic conductivity on crust covered and crust-free surfaces was collected and compared to results of commonly used methods to retrieve spatially distributed Ks data. Results reveal that methods typically used for estimating Ks, such as exponential decay functions or pedo-transfer functions (PTFs), can be inadequate in such regions. The analysis shows that in our study area the presence of surface crust is the dominating factor for determining the spatial distribution of Ks. Furthermore, the results reveal that remote sensing data can provide useful information for estimating surface Ks values as it could be successfully applied for the spatial detection of surface crust characteristics. [ABSTRACT FROM AUTHOR]

Soil surface roughness (SSR), a description of the micro-relief of soils, affects the surface storage capacity of soils, influences the threshold flow for wind and water erosion and determines interactions and feedback processes between the terrestrial and atmospheric systems at a range of scales. Rainfall is an important determinant of SSR as it can cause the dislocation, reorientation and packing of soil particles and may result in the formation of physical soil crusts which can, in turn, affect the roughness and hydrological properties of soils. This paper describes an experiment to investigate the impact of a multi-day rainfall event on the SSR and physical crusting of very fine soils with low organic matter content, typical of a semi-arid environment. Changes in SSR are quantified using geostatistically-derived indicators calculated from semivariogram analysis of high resolution laser scans of the soil surface captured at a horizontal resolution of 78 μm (0.078 mm) and a vertical resolution of 12 μm (0.012 mm). Application of 2 mm, 5 mm and 2 mm of rainfall each separated by a 24 h drying period resulted in soils developing a structural two-layered ‘sieving’ crust characterised by a sandy micro-layer at the surface overlying a thin seal of finer particles. Analysis of the geostatistics and soil characteristics (e.g. texture, surface resistance, infiltration rate) suggests that at this scale of enquiry, and for low rainfall amounts, both the vertical and horizontal components of SSR are determined by raindrop impact rather than aggregate breakdown. This is likely due to the very fine nature of the soils and the low rainfall amounts applied. [ABSTRACT FROM AUTHOR]

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

• Photoautotrophic cyanobacteria colonize quartz clasts in the hyperarid Namib Desert. • Hypolith colonization is affected by clast thickness and mean annual rainfall. • Soil organic carbon is elevated under colonized quartz clasts. • Hypoliths account for substantial soil organic carbon at the landscape level. Carbon (C) in soils accounts for a substantial and dynamic portion of the global C cycle, with concentrations of soil organic carbon (SOC) typically closely linked to vascular plant productivity. However, C fixed by non-vascular photosynthetic organisms may account for a sizeable proportion of SOC in locations where vascular plants are not abundant. In the hyperarid Namib Desert, vascular plant growth is very limited and largely ephemeral. Extreme abiotic conditions even limit establishment of cyanobacterial soil crusts, with photoautotrophic cyanobacteria largely restricted to the undersides of translucent quartz clasts that buffer environmental extremes. The importance of these 'hypoliths' in enhancing SOC pools, and how this may vary with climate and clast physical characteristics, remains unknown. We worked across a rainfall and fog gradient in the central Namib to assess quartz clast size and distribution, factors affecting the probability of hypolithic colonization, and the landscape-level influence of hypoliths on surface SOC pools. Clast colonization increased with clast thickness and with increasing mean annual rainfall. SOC and chlorophyll a (a proxy for cyanobacterial biomass) concentrations were greater under colonized quartz clasts than under non-quartz clasts or in bare soil. Landscape-level SOC, estimated by combining SOC concentration with the distribution and colonization of quartz clasts, was greatest at the site with the highest rainfall and lowest at a mid-gradient site with moderate rainfall and fog. Climate change scenarios that promote quartz colonization have the potential to double SOC pools at the mid-gradient site, although SOC changes would be more muted at other sites. Low vascular plant and biocrust cover in the Namib Desert allows hypolithic communities to play an outsized role in SOC pools; a loss of all hypolithic cyanobacteria would lead to 10–20% declines in surface SOC pools. Future climate change has the potential to shift surface SOC if it alters cyanobacterial colonization of quartz. [ABSTRACT FROM AUTHOR]

The hyperarid Atacama Desert contains numerous local basins with surficial salt crusts, known as salars, where evaporation of shallow groundwater drives the major soil processes. We examine chemical and isotopic profiles in two soils of differing ages from the Salar Llamara to determine the geochemical processes involved in their formation. Evaporation, which provides salts to the soils through mineral precipitation, decreases with increasing salt crust thickness, and average ~ 0.03 mm m − 2 d − 1 over geological time frames. Salt distribution varies predictably with depth and soil age, with the most soluble compounds concentrated nearest to the land surface, indicating the direction of fluid flow. δ 34 S values of mineral sulfate tend to decrease with decreasing soil depth, following a pattern indicative of Rayleigh-like fractionation as solute-rich waters migrate toward the land surface. δ 13 C and δ 18 O values of carbonate suggest that the uppermost halite layers, which contain very small amounts of carbonate, have a strong biological signature. In contrast, carbonate-rich layers deeper in the profiles consist of largely unmodified lacustrine carbonate that formed in highly evaporitic lake conditions. The continuous upward evaporation of water and dissolved solutes creates a rugged and physically dynamic halite crust composed of rounded salt nodules. The crust undergoes deliquescence as atmospheric relative humidity rises from marine air intrusions, and we found that the halite nodules on the surface of the Salar Llamara are nearly always at or above deliquescence relative humidity. The interiors of these nodules are therefore able to buffer the large diurnal changes in atmospheric relative humidity allowing for the survival of halophilic microbial communities in an otherwise very dry environment. Radiocarbon measurements of occluded organic C in the surface crusts indicate that C cycling occurs at differing rates depending on local micrometeorological conditions, and that a given salt crust feature may persist for thousands of years once formed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synchrotron 2D-µXRD mapping used for clay mineral characterization in soil crust. • Novel methodology first validated on a laboratory-made clay-rich sample. • Methodological approach successfully applied on natural soil crust. • Innovative method for unraveling deposition mechanisms in soil crust. Our understanding of soil crusting and its detrimental consequences is mainly based on the analysis of morphological changes occurring at the soil surface. Such changes are usually assessed at spatial scales ranging from a few millimeters to that of the field. The inner-reorganisation within the topsoil during soil crusting primarily involves the redistribution of clay particles. Their mineralogy and arrangement remain however delicate to determine by the sole use of microscope observations. To overcome these limitations, we developed an innovative methodology based on synchrotron 2D micro X-ray diffraction (2D-µXRD) to map relevant parameters related to the organisation of all types of soil clay minerals, i.e. relative diffracted intensities, degree of preferential orientation, mean deviation angle from the surface. Our methodological strategy was first validated on a laboratory-made model sample, composed of various pure clay phases with clear preferential orientations. Then, a vertical section of soil crust from long-term bare fallow (LTBF) experiment of the France's National Research Institute for Agriculture, Food and Environment (INRAE, Versailles, France) was studied. Micromorphological features of the soil crust were first described by using conventional scanning electron microscopy. Synchrotron 2D-µXRD analyses were then successfully applied on the same region of interest. The in-depth analysis provided by the synchrotron 2D-µXRD approach revealed the presence of clay microlayers that were not observed on SEM images. Additionally, clay mineralogy as well as preferred clay-particle orientation and overall alignment highlighted specific quantitative structural signatures. These signatures involved the discrimination between clay microlayers associated to the settling of clay particles in microdepressions and clayey microaggregates resulting from transportation of pre-existing soil crusts. This new technique has led to re-interpretation of the deposition mechanisms in the natural soil investigated here and opens wide perspectives for in-depth detailed characterization of clay mineralogy in soil crusts. [ABSTRACT FROM AUTHOR]

This study analyzes the most suitable methods for detecting and measuring the soil sealing change caused by urban growth in the city of Madrid, Spain, using remote sensing techniques and GIS. Some irreversible, negative effects of soil sealing are impermeable ground and modified ecosystems (bio-geochemical cycle, water cycles, loss of biodiversity, etc.), which alter matter and energy flows and the ecological functions of the soil. Urban development has often been more concerned with viability and financial profit, to the detriment of the environment. Multi-temporal studies on the processes are assisted by several types of technologies providing geographical information, together with large cartography, photogrammetric and satellite databases. The best soil sealing detection is carried out based on principal component analysis of the images and the SAVI index. Supervised classifications show that from 1984 to 2013 soil sealing in the municipality of Madrid and its surroundings has risen from almost 15% to 24%, an increase of 9%. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) have been recognized as a vital influence factor to desert terrestrial ecosystems under semiarid climate. However, their effects on soil moisture and temperature, which play very important roles in many ecological and hydrological processes, have not yet been well understood. To provide more insight into this issue, we conducted a five-year monitoring experiment for moisture (0–150 cm) and temperature (0–30 cm) of soil with or without moss-dominated BSCs in a semiarid ecosystem on the Loess Plateau of China. The results showed that: (1) the BSCs significantly increased soil moisture by up to 7.6% at 5 cm depth, and significantly decreased soil moisture by up to 3.1%, 6.1%, and 8.1% at 15, 30, and 50 cm depths, respectively; while they had nearly no influence on soil moisture at 70–150 cm depths; (2) the BSCs significantly decreased soil temperature by up to 11.8, 7.5, 5.4, and 3.2 °C at 0, 5, 15, 30 cm depths, respectively, under wet and hot conditions in summer; whereas they significantly increased soil temperature by up to 8.0, 3.7, 2.9, and 1.9 °C, respectively, under dry and cold conditions in winter; and (3) the effects of the BSCs on soil moisture and temperature were significantly correlated with each other, and both of them were significantly driven by solar radiation and precipitation. We concluded that soil moisture and temperature regimes were significantly changed by moss-dominated BSCs in semiarid ecosystems, however, their effects mostly depended on seasons and soil depths. [ABSTRACT FROM AUTHOR]

Abstract: Many methods and indices have been developed for assessing seal formation. However, difficulties persist in selecting a suitable method because of the effect of the procedure on the results. The present study aims to evaluate appropriate soil sealing assessment methods that enable to distinguish the surface condition of soils with contrasting characteristics. A comparative study was conducted among the most frequently used methods, viz: wet sieving tests, raindrop impact tests under field and laboratory conditions, penetration resistance (PR), consistency index (C5–10), soil stability index (StI), and crusting index (CI). Different agricultural Venezuelan ‘tropical’ soils were ranked according to their susceptibility to soil sealing. The ranking and the correlation between the parameters were used to assess and compare soil sealing formation measured by the different methods. According to multiple and single wet sieving tests the soils were classified into two groups as stable (kaolinitic-rich) and unstable (smectitic-rich) soils. The ranking of the soils and correlation analysis (p<0.05) indicated that aggregate stability as determined by wet sieving, infiltration rate, runoff and soil loss under laboratory and field conditions was effective in predicting seal formation among smectitic-rich loam to kaolinitic-rich clayey soils. C5–10 and PR were not comparable tests for sealing formation (p>0.05). The StI that considers soil organic matter (SOM) as the most important factor to maintain soil structure did not reflect the high stability of the kaolinitic-rich soil that lacks SOM. The CI, which indicates the risk for soil crusting formation in the function of silt fractions, is a more capable indicator for evaluating susceptibility to sealing of our soils. This study further proposes that when topsoil aggregates are characterized by high silt and smectite contents the use of wet sieving and raindrop impact tests or simple indices such as StI and CI can satisfactorily assess the susceptibility to seal formation. Differences obtained in seal formation ranking indicated that method selection impacts the measured value. It can therefore be recommended to take the effect of the method into account when interpreting the results obtained. [Copyright &y& Elsevier]

Abstract: Landsat TM images are used to define soil sealing in the Madrid Autonomous Region (Spain) between 1989 and 2010. The comparison of images within this time frame obtains an estimated loss of 42,800ha of agricultural land. Soil sealing mainly occurred in metropolitan areas as well as in the E, SW and NW of the capital. Landsat images overlaid on agrological classification maps and soil association maps show that the most significant losses correspond to agricultural classifications B and C and luvisols associated with cambisols, regosols, calcisols and fluvisols (WRBSR, 2007). [Copyright &y& Elsevier]

Abstract: Arid and semiarid crusted ecosystems occupy a large extent of the Earth''s surface. In these ecosystems there is a delicate balance between C sequestration and biodegradation that could easily be altered due to human disturbance or global warming. These environments are characterized by the presence of biological soil crusts (BSCs) coexisting with shrubs in the interspaces. BSCs play an important role in the C-cycle in arid and semiarid areas, but there has been little research regarding C-storage in crusted soils. In this research, representative BSCs were studied in three different crusted semiarid ecosystems in Southern Spain. Chemical fractionation and characterization of the organic matter in BSCs and underlying soils were undertaken to compare the total amount and quality of humic substances and find surrogate indicators of the soil organic matter quality. After isolating the major organic fractions (particulate fraction, humic acid-like (HA) and fulvic acid (FA)), the macromolecular, HA fraction was studied by derivative visible spectroscopy and resolution-enhanced infrared (IR) spectroscopy. Our results show quantitative differences in organic matter fractions, in agreement with the structural characteristics of the HA-type substances. The more stable crusted ecosystem with more evolved vegetation cover tend to be associated with HAs with broadband IR profiles, high optical density and macromolecular condensation and presence of polycyclic fungal biomarker compounds. In contrast, in the crusted ecosystem with very low or almost absent vascular vegetation cover, the C sequestration depends almost exclusively on the activity of crust-inhabiting organisms. It is suggested that the organic matter in BSCs shares characteristics with aquatic humic matter derived from non-lignified plants, including structurally complex HA-type substances which may have been originated by abiotic condensation of unsaturated lipids and/or diagenetic alteration of aliphatic biomacromolecules. Although these humification mechanisms have not been extensively studied in terrestrial soils they may be very active mechanisms for C sequestration in some types of crusted ecosystems. In particular, the spectroscopic characteristics in the visible and IR ranges of the crust-isolated HA-type substances provide the above-indicated biogeochemical proxies informing on the organic matter stability and quality and their bearing on the potential of crusted ecosystems for maintaining their properties after external disturbance. [Copyright &y& Elsevier]

Abstract: Dictating the length of time during which water is available, evaporation plays a cardinal role in ecosystem ecology and structure. This is especially so in arid and semi arid zones, where precipitation is highly limited. Covering the surface with a distinct 1–10cm thick layer, biocrusts (called also biological soil crusts or microbiotic crusts) may affect the evaporation rate and hence the water loss of the underlying parent material. Owing to their wide occurrence in arid and semi arid regions, examination of their impact upon the evaporation rate of the underlying soil is of special importance. The evaporation of water from sand covered by four types of cyanobacterial crusts and one moss-dominated crust in the Negev Desert was examined along with bare sand. The crusts and sand were subjected to wetting by rain and sprinkling (in Petri dishes and within 25cm diameter plots), and the crust and subcrust temperatures and moisture content were measured. In addition the albedo of the crusts was also measured. Whereas thick and high-biomass crusts tended to retain higher amounts of water in the Petri dishes, they were found to increase subsurface temperatures (by up to 3.9°C at 5cm depth) under field conditions, subsequently decreasing the 0–10cm moisture content. Moisture content at the crusted plots was significantly lower than that of non-crusted plot, with crusted plots having an evaporation rate of 1.24–1.57 (with average of 1.38) times higher than the bare sand. These findings were supported by field measurements under natural rain precipitation. In both cases, the field data under sprinkling and rain precipitation showed that the non-crusted surfaces retained their available moisture at the upper 10cm of the soil profile for 5–7days longer than that of the crusted surfaces. The findings may explain contradictory data published in the literature regarding field and lab experiments, and may point to the negative effect that biocrusts may have upon the soil water budget and hence on water availability for higher plants. [Copyright &y& Elsevier]

Abstract: Soil ecosystem engineers are major actors of soil macroaggregation, a process that drives the production of ecosystem services by soils. However, our inability to identify the origins of different types of macroaggregates found in soils is an obstacle to describing and modeling their dynamics and associated processes (C sequestration; hydraulic properties). This laboratory study investigated mechanisms of biological soil macroaggregation by two different earthworm species (Apporectodea caliginosa (Savigny) and Allolobophora chlorotica (Savigny) and two plant species (Trifolium pratense, Plantago lanceolata L.), in isolation and in all possible combinations. Near infrared (NIR) spectral analysis significantly discriminated macroaggregates according to the organisms that created them since each organism produced macroaggregates with distinct NIR signals (p<0.001). The largest departure from the control signal was observed with T. pratense whereas earthworms and P. lanceolata specific signals were less contrasted. Macroaggregates formed in the presence of more than one ecosystem engineers had mixed signals showing that several actors had participated in their construction. This means that roots and earthworms did not produce macroaggregates in isolation and rather added their effects in building structures of mixed origins. Further studies based on the present methodology will tell us more on below ground behaviors of ecosystem engineers and their interactive building of soil habitats. [Copyright &y& Elsevier]

Abstract: There are increasing concerns that climatic and land use changes will enhance soil respiration rates and soil organic carbon loss, compromising agricultural productivity and further elevating atmospheric CO2. Current understanding of dryland respiration is, however, insufficient to enable prediction of the consequences of these changes for dryland soils and CO2 fluxes. The objectives of this paper are to present in-situ respiration data from five remote sites along a climatic gradient in the Kalahari of Botswana and to determine the effects of temperature, moisture and biological crust cover on soil CO2 fluxes. Moisture was the primary limiting factor to efflux which increased with amount of simulated rainfall. On dry soils, mean CO2 efflux was between 1.5 and 5.9mgC m−2 h−1. After 2mm and 50mm simulated wetting, mean rates increased to 4.0 to 21.8 and 8.6 to 41.5mgCm−2 h−1 respectively. Once wet, soil CO2 efflux increases with temperature, and sites at the hotter northern end of the transect lost more CO2 than cooler southerly sites. Net respiration rates are, however, muted by autotrophic organisms in biological soil crusts which photosynthesise and take up CO2. The temperature sensitivity of soil CO2 efflux increased with moisture. Dry, 2mm and 50mm treated soils had a Q 10 of 1.1, 1.5 and 1.95 respectively. Our findings indicate that higher temperatures and a loss of biological crust cover will lead to greater soil C loss through respiration. [Copyright &y& Elsevier]

Abstract: Biological soil crusts occur extensively in semi-arid regions. In the western part of Niger, they are associated with various types of physical soil crusts in fallows and in the “tiger bush ecosystem” (a landscape with a typical banded pattern consisting of densely vegetated bands of small trees and shrubs alternating with bare soil bands). Despite their widespread occurrence, not much research has been done regarding their role on runoff generation in the Sahelian environment. The present study aims at: (i) highlighting the relative contribution of biological soil crusts in infiltration and runoff on crusted soil in respect with other soil factors; (ii) assessing the impact of underlying physical crusts associated with a wide range of microbial cover; and (iii) gathering the data required for an evaluation of the potential of microbial cover in water redistribution in an arid environment and for modelling purposes. The study was based on runoff measurements performed in situ at the level of ten plots, 1m2 each, under two simulated rainfalls. Those experiments were coupled with the visual characterization and image analysis of soil surface conditions as well as micromorphological examinations, using a light microscope, both on the field and at the laboratory. Visual estimation of crust cover was found consistent with the estimation based on the image analysis. Biological soil crusts capped the summit of pre-existing physical soil crusts, i.e. structural crusts, formed in situ by the impact of water drop and erosion crusts, resulting from water or wind erosion of structural crusts. The percentage of microbial cover in the 1-m2 plots range from 39 to 80% (55% in average) on structural crusts compared to 4 to 29% (17% in average) on erosion crusts. Runoff coefficient varied with both the level of microbial cover and the type of physical soil crust. Higher runoff coefficients were found where biological soil crusts had developed on erosion crusts as compared to structural crusts. Runoff coefficients recorded from erosion crusts increased with the level of microbial cover while negative correlations were found on structural crusts. They show that the clogging effect of microbial cover for the plasmic layer of erosion crusts is higher than that of the sand layer of structural crusts. Separating biological soil crusts according to the types of the underlying physical crusts explain, therefore, the contradictory findings related to their role on infiltration and runoff generation. Those data will help to evaluate the potential role of biological soil crusts in the modelling of water redistribution in the arid environment of the western part of Niger. [Copyright &y& Elsevier]

Abstract: Afforestation was one of most successful measures to rehabilitate desertified lands and to improve regional eco-environments in the Horqin Sand Land. A field experiment was conducted during 2005 and 2006 in the Horqin Sand Land to investigate the effects of Populus simonii plantation growth on soil crust formation and topsoil properties. The results showed that plantation establishment promoted the development of biological soil crust and improved properties of topsoil 0–5cm under the crust in sand dunes. As the plantation aged, soil crust developed gradually from a physical crust, to a lichen crust and then to a moss crust and crust coverage, thickness, hardness, very fine sand content, clay, silt, organic carbon and nutrients increased significantly. Clay, silt, organic carbon and nutrients in topsoil 0–2.5cm and 2.5–5.0cm under the soil crust increased with plantation age and crust development, but the magnitude of changes decreased with increasing soil depth. Changes in soil physical and chemical properties in the crust had a significant positive correlation with plantation age, and changes in physical and chemical properties in the 0–5.0cm layer of topsoil had a significant positive correlation with soil crust development and plantation age. Soil crust development and changes in topsoil properties under the soil crust can be attributed primarily to the reestablishment of vegetation and the duration that the vegetation is in place. [ABSTRACT FROM AUTHOR]

Abstract: Surface crusts represent a major limitation for reclamation projects in arid regions. With the advancements in spatial and radiometric resolution, infrared thermography is a potential technique for non-destructive characterization of soil crusts. The objective of this study is to evaluate time-resolved thermography, within the context of the composition by XRD, and configuration, by X-ray CT, of intact soil crust samples. Three samples were obtained from Dara region, west Gulf of Suez, the Eastern Egyptian Desert, representing the surface crusts formed in the Dara piedmont plain and Dara dry valley, as well as bedrock specimen found deep in Dara piedmont plain soil profiles. A step-heating test was applied to all samples with duration of 420min. Temperate–time plots indicate that surface temperature reached an approximate temperature of 60 °C for all three samples after being heated for 270min, the minimum surface temperature (58.3°C) was obtained for the bedrock specimen because of large quartz content (64%) and weak development of pore space (1.3% of total volume). The slope of the early linear phase of temperature plotted against the square root of time was found to be steeper in the case of Dara piedmont plain and valley crust specimens (3.82, 3.84, respectively) than the slope obtained by scanning the bedrock specimen (3.32). Remarkably, despite the differences in composition of surface crust found in the Dara piedmont plain and valley, their surface temperature patterns were found to be similar. The similarity in thermal response is explained by the overlap in estimated thermal inertia range from the XRD and X-ray CT data. This final result demonstrates that the results of time-resolved thermography technique are not self-exploratory and ancillary data such as X-ray CT is needed for interpretation. [ABSTRACT FROM AUTHOR]

Abstract: The physical nature of sediment transport favors the movement of smaller and less dense materials, typically resulting in greater (enriched) sediment total phosphorus (TP) and organic matter (OM) concentrations than those of the parent soil. In rainfall–runoff, residue cover significantly influenced P enrichment, with the median TP enrichment ratio (TPER) for corn-grain (1.4) being significantly greater (p =0.007) than that for corn-silage (0.8) and manured corn-silage (1.0) fields, which were similar. While greater P enrichment was observed in snowmelt compared to rainfall–runoff, attributable to correspondingly high OMER values, TPER was unaffected by treatment differences (p =0.60). The OM enrichment was much higher (~10×) during snowmelt (9.7) compared to rainfall–runoff (0.97). Low flow rates over frozen surfaces may have favored enhanced transport of OM and clay-sized particles in snowmelt. Crop residue contributions from corn-grain systems favor greater transport of organic P forms (i.e., low dissolved reactive P/total dissolved P ratios) whereas inorganic P dominance was observed in silage fields. Additional intra-event runoff data generated for fields with different crop-row orientations (contour vs. up-and-down the slope) provided more insights into the temporal dynamics of P enrichment process. The TPER values were generally inversely related to flow rate and soil loss. This study addresses crucial knowledge/information gaps on the role played by the mode of runoff generation (rainfall–runoff vs. snowmelt) and field roughness conditions (due to crop residue, crop-row orientations) on P enrichment from row-cropped agricultural systems. [Copyright &y& Elsevier]

• Nutrient status was influenced by snow depth, crust type and its interaction. • Variation of snow depth had negative effects on nutrient status of biocrusts. • A cascading effect on biocrusts development may cause by change of snow depth. Winter snowfall is an important water resource for organisms in desert ecosystems. Changing snow depth is expected to exert a potential influence on growth and ecological functions of biological soil crusts (BSCs), which are known as a dominant functional vegetation unit of desert ecosystems. However, limited attention has been paid to this potential effect on BSCs. A field simulation experiment was conducted to measure the water content, nutrient concentrations (organic carbon; total nitrogen; available nitrogen; available phosphorus; available potassium; ammonium nitrate; and nitrate nitrogen), and microbial biomass (carbon, nitrogen, and phosphorus) in samples (cyanobacterial and lichen crusts and subcrust soil) under snow cover of different depths after a four year experiment (from October 2013 to April 2017) in the Gurbantunggut Desert. The results showed that water content increased with increasing snow depth (P < 0.05). Snow removal and snow cover reduction decreased nutrient and microbial biomass concentrations in both biocrust types (P < 0.05). The concentrations of most measured nutrients and microbial biomass decreased significantly when snow depth was increased to twice ambient conditions (P < 0.05). Moreover, the concentrations of nutrients and microbial biomass were significantly influenced by snow depth (P < 0.05), crust type (P < 0.001), and their interaction (P < 0.05). The results demonstrated that variation in snow depth adversely affect the carbon and nutrient availability and microbial biomass in BSCs. Such changes might lead to a cascading effect in species composition and function of BSC communities in arid regions. [ABSTRACT FROM AUTHOR]

• We provide comprehensive data of SOC for managed land use in Austria. • SOC densities are highest in peatlands forests, and partially in grasslands. • Cropland soils are already managed to conserve the SOC stock. • The data serve as reference for the effect of future land management concepts. • Efforts to increase the SOC stocks are hampered by soil sealing. We compiled information from different sources in order to establish a comprehensive map of the stock of soil organic carbon (SOC) in the upper 30 cm under different forms of land use for Austria. The information serves as a baseline for the evaluation of the potential of climate-change mitigation measures. SOC sequestration plays an important role in the discussion of terrestrial carbon (C) sinks and the size of the SOC pool is one of several quality measures for crop production and the national and regional food security. The baseline serves also for the evaluation of the effectiveness of adaptive land management in order to cope with climate change. Austrian croplands, grasslands, forests, and settlements contain 300 Mt SOC. Peatlands have the highest SOC density (220 t C/ha), yet cover only about 2% of the country. Forest soils store 106 t C/ha and comprise the largest pool due to the coverage of more than 4 Mha (48% of the country). Intensively and extensively managed grasslands cover 0.8 Mha (10%) and contain between 91 and 113 t C/ha, and cropland on 1.28 Mha (15%) hold on average 62 t C/ha. Due to the geographic heterogeneity of Austria with respect to climatic conditions, geology and soils, and topography the regional differences in SOC stocks are large. Measures to increase the SOC stock in cropland have been applied for 25 years within agri-environmental and climate-smart strategies. An increase of the total SOC pool is expected due to the afforestation and reforestation of marginal agricultural land and to a smaller extent due to the restoration of peatlands. A decline of the SOC stock is a consequence of land development for settlements and infrastructure. [ABSTRACT FROM AUTHOR]

[Display omitted] • BSC development favours soil formation and accumulation of TOC and TN. • BSC supply modern organic C to soil, so diluting the old C inherited from the substrate. • Soil acidification and mineral weathering increase with the BSC development degree. We tested the impact of biological soil crusts (BSC) at different degrees of development on soil formation in Polar ecosystems, specifically in two Arctic sites, Svalbard Island (Norway) and Tarfala (Sweden), and in an Antarctic site, Apostrophe Island (Victoria Land). In each site, slightly developed BSC (thin and made by green algae and cyanobacteria associations – SD-BSC) highly developed BSC (thick and dominated by green algae and cyanobacteria associations with/without mosses and/or lichens – HD-BSC), and moderately developed BSC (MD-BSC) with intermediate characteristics between the slightly and the highly developed, were sampled together with the AC and A horizons immediately under the crust. After separating the organic residue of the biocrust from the mineral phase by density fractionation, in the heavy fractions obtained from HD-BSC, MD-BSC and SD-BSC we determined the amount of soil organic carbon and its radiocarbon natural abundance, total nitrogen content, mineralogical assemblage by x-ray diffraction, and quality of soil organic matter (SOM) by infrared photoacoustic spectroscopy (FTIR-PAS). We found that when BSC were able to develop on stable ice-free surfaces, they modified the soil by supplying new organic substances. These new substances, in addition to diluting the old C inherited from the substrate and darkening the upper mineral horizon, promoted acidification, which is responsible for mineral weathering and neogenesis of clay minerals. With their development, BSC act as ecosystem engineers and promote soil formation in Polar ecosystems by increasing soil stability, organic matter content and nutrient availability, which indirectly improve aggregation, water holding capacity, and soil heating. [ABSTRACT FROM AUTHOR]

Abstract: Soils and sediments of the southern Aral Sea basin of Central Asia are commonly covered by salt-bearing surface crusts. These crusts represent a potential source of salt-rich dust that can contribute to salinisation of soils in a large area. Crust types include takyric crusts, surface crusts on Solonchaks, and salt crusts covering dry parts of the lake bed. The takyric crusts are structural crusts, showing features related to flooding and shrinkage. Gypsum, formed within the sediment matrix, is the only evaporite mineral they contain. One studied Solonchak crust is fine-grained, with a thin thenardite and bloedite coating along the irregular surface and halite coatings along the sides of pores. All salts in this crust formed by evaporation of solutions contained in the groundmass. A Solonchak crust with a sandy texture contains prismatic gypsum crystals that formed in a water-saturated surface layer, as well as bloedite, eugsterite and halite, formed by evaporation of interstitial brines. The lake bed crust is a pure accumulation of salt minerals (bloedite, hexahydrite, halite, kainite), with synsedimentary and diagenetic features. Salt mineral assemblages in the three crust types are those that form during successive stages of evaporation of Aral Sea waters, in agreement with published theoretical predictions. [Copyright &y& Elsevier]

Abstract: Microscopic examination of microbiotic soil crust shows that the profiles of soil with a dense cyanobacterial cover had two different layers: a surface thin layer composed of aeolian-born materials and an organic layer formed by filamentous cyanobacteria associated with sand particles. The results indicate that microbiotic cover is an important determinant of sand fixation in the Gurbantunggut Desert, northern part of Xinjiang, Northwestern China. Microscopic examination of microbiotic crusts in this study revealed an intricate network of filamentous cyanobacteria and exopolysaccharides, which binds and entraps sand grains and conglutinate fine particles with each other. Resistance to wind erosion paralleled the different disturbance levels on microbiotic soil crust. Sandy soil surface disturbances resulted in greatly decreased soil resistance to wind erosion. Maximum wind tunnel velocity in this test (25 m s−1) did not lead to any wind erosion on the surface of undisturbed microbiotic soil crust, i.e. 100% covered by microbiotic soil crust. As for different disturbance levels, the highest threshold friction velocity was seen in the sand surface with 10% disturbance of microbiotic crust. The surface microbiotic soil crusts have great effects on wind erosion rates. Wind erosion rates for sandy soil with 0% crust cover was about 46, 21, 17 times the soil with 90% crust cover at wind velocities of 18, 22, 25 m s−1, respectively. This study confirms that the planners and managers of nature reserves in this area should understand the important ecological roles of microbiotic crust in desert ecosystems. The reduction of trampling on the soil will eventually result in the re-establishment of biological crusts and their associated organisms, and ultimately lead to lower levels of wind erosion. Additionally, strategies should be developed to manage livestock and oil exploration in order to avoid concentrated zones of impact. [Copyright &y& Elsevier]

Savannas and grasslands in South Africa are adapted to fire, yet long-term effects of fire on soil, water and nutrients remain largely unknown. To determine whether frequent burning increases the tendency of soils to crust and alters soil chemistry, topsoils from 19 sites were examined in Mpumalanga, KwaZulu-Natal and the Eastern Cape where annual burning and fire exclusion experiments had been conducted for at least 28 years. A comparison of soils from burnt and unburnt plots revealed that composite samples taken to a depth of 10 cm from burnt plots had lower laboratory infiltration, electrical conductivity (EC) of 1:5 extracts, water-soluble K, water-soluble NH4, total C, total N and labile C. Burnt plots had higher pH in KCl, water dispersible clay and modulus of rupture. Rate of soil respiration from composite samples (0–2 cm) from burnt plots was lower than from unburnt plots (means of 21 vs. 36 ng C g-1 s-1). Rainfall simulation on the same samples demonstrated that burnt plots crusted more rapidly than unburnt plots (19 vs. 35 mm h-1), while results from sampling at 1-cm intervals revealed that the greatest differences between burnt and unburnt plots were in the 0–1 cm layer. The top few centimetres of soil are likely to have a disproportionate effect on ecosystem functioning by influencing the rate of infiltration and mineralisation of soil organic matter. This thin surface layer has been named the pedoderm in this paper. Soil from 0–1 cm in burnt plots had lower total C (means of 0.8% vs. 2.7% for burnt and unburnt plots, respectively), total N (0.07% vs. 0.23%), (NH4)OAc-extractable Ca (7 vs. 17 mmolc kg-1), Mg (2 vs. 7 mmolc kg-1), K (0.8 vs. 1.5 mmolc kg-1) and a greater exchangeable Na percentage (17% vs. 8%). The results indicate that burning increases soil crusting. This was ascribed to a decrease in humus content (and associated disaggregating effect) and an increase in the dispersion of clay. Nutrients are lost from burnt plots over time, probably by the removal of ash in surface runoff. Calcium, Mg, and K were lost more readily than Na probably because plants take up these nutrients in greater concentration than Na. The net effect was an increase in the exchangeable sodium percentage (ESP). Crusting on burnt plots may be self-perpetuating, because increased runoff is likely to increase the loss of soluble salts. [Copyright &y& Elsevier]

Micromorphological techniques have frequently been used to describe processes leading to surface crusting. Image analysis can be helpful in quantifying changes in porosity necessary for estimating hydraulic parameters in crust infiltration models. The objective of this study was to quantify changes in pore area and frequency for three pore shapes (round, irregular, and elongate) and four size classes (50–200, 200–350, 350–500, and >500 μm). Porosity decreased exponentially as the surface was approached from a depth of about 10 mm. The number of pores was roughly inversely proportional to pore area as larger pores were fragmented into numerous small pores. Intermediate-sized (350–500 μm) elongate pores were the most sensitive to crusting processes, and these were divided into small (50–200 μm) and small intermediate (200–350 μm) round pores. Changes in pore shape and size distribution make estimating crust hydraulic conductivity and thickness extremely difficult, but a thickness of 5 mm appears to be a reasonable estimate for modelling purposes. [Copyright &y& Elsevier]

A detailed pedological study in an apparently homogeneous badlands area of gypsiferous mudstones in the Tabernas Desert (Almerı´a, SE Spain), with an annual precipitation of 200 mm, has been shown to be composed of different soil units belonging to different stages of soil development. Twenty-four soil profiles in four topographic transects within a small instrumented catchment have been described and analysed, along with over 100 probings and observations. A complementary approach to ascertain the relationships of soil-units with topography made use of a 1-m resolution digital elevation model (DEM) and derived terrain attributes. Moreover, the relationships with soil cover, surface hydrology and erosion have all contributed to understanding pedogenic and evolutionary processes. The five soil units identified correspond to distinct topographic positions, from steep S-oriented slopes with incipient soil development under bare surfaces (Epileptic Regosol), to moderately sloping, N-oriented soils, fairly well developed below a dense cover of annual and perennial plants (Haplic Calcisol). Both the spatial distribution and the topographic position of soil units favour gypsum and salt washing processes and gypsum accumulation is restricted to higher positions with very small contributing areas and minimum overland flow and thus reduced leaching. Gypsic horizons and Gypsisols, while previously described in the area associated to gypseous rock outcrops, are now described associated to gypsiferous mudstones. [Copyright &y& Elsevier]

• The mobility of eroded casts was assessed on uncrusted and crusted hillslope soil. • A small proportion of sediment from eroded casts was mobile on the uncrusted soil. • Mobility of dispersed sediment increased markedly on the crusted soil. • Soil crusting influences surface hydrology, increasing mobility of dispersed casts. • Bulk soil continued to act as a sediment-source under crusted surface conditions. Whilst evidence has been found that dispersed earthworm casts can act as a sediment-source on fully vegetated hillslopes, uncertainty still remains over the mobility, and hence, the ability of such material to similarly act as a sediment-source on cultivated hillslopes. This study reports preliminary findings from a prototype sediment tracing technique to assess the mobility of eroded earthworm casts on the same unconsolidated (i.e. uncrusted) and crusted hillslope soil using two different artificial radionuclides. A 0.75 * 0.75 * 0.1 m erosion plot, pitched at a 10% slope (5.7°) was filled with bulk soil and textured to simulate an agricultural-type seedbed finish. A total of 56 similarly-sized casts representing 197 g of sediment (dry weight) were labelled with 430 Bq of caesium-134 activity, evenly distributed across the unconsolidated soil and subjected to ca. 15 mm hr-1 of simulated rain until casts disintegrated, during which time surface runoff was collected continuously. Soil was air-dried to allow a surface crust to form and then a further 56 similarly-sized casts representing 198.5 g of sediment (dry weight) were labelled with 433 Bq of cobalt-60 activity, evenly distributed across the crusted surface and again, subjected to simulated rainfall until their complete disintegration. Surface runoff was continuously collected. An unmixing model was used to partition labelled sediment from unlabelled bulk soil. For the 1st rainfall event, 20.6 g of 134Cs-labelled material, representing 10.5% of the total mass deployed, was removed by surface runoff from the unconsolidated surface. During the 2nd rainfall event, a further 16.2 g of 134Cs-labelled sediment (8.2%) was removed from the crusted surface, along with 73.1 g (36.8%) of 60Co-labelled sediment. In comparison with 134Cs-labelled material, approximately double the amount of 60Co-labelled sediment was eroded from the crusted soil in approximately half the rainfall exposure time. These findings, although very preliminary, firstly provide proof-of-concept confirming the efficacy of the tracing technique and secondly, suggest that cast-derived material is not only mobile on cultivated hillslopes, but the degree of mobility and hence the source-potential of the eroded material increase markedly when soil surface conditions change from unconsolidated to crusted. [ABSTRACT FROM AUTHOR]

• Biocrust species composition differed among the three geomorphic zones. • Biocrust taxa in the runoff zones had a greater capacity to trap water and sediment. • Grazing had no effect on biocrust communities among the three geomorphic zones. • Resource acquisition by biocrusts may maintain patterned dryland environments. Spatial patchiness in resources is a pervasive feature of drylands worldwide. This patchiness manifests itself as two distinct geomorphic zones that are characterised by the loss (runoff) or gain (runon) of resources such as water, seed and organic matter. Most studies have examined how vascular plants vary across these two distinct zones, but there are few studies of the non-vascular components of these patterned landscapes. We examined the distribution of soil crust lichens and bryophytes (moss, liverworts) in relation to three geomorphic positions within a patterned Acacia aneura woodland grazed by sheep and kangaroos. We found that the distribution of biocrust taxa was strongly related to geomorphic position, with lichens dominating the runoff zones and liverworts restricted to the runon areas (groves). The runon zones were characterised by a greater cover of litter, and greater species richness, cover, and functional richness of biocrusts, while biocrusts in the runoff zones had greater functional diversity and dispersion. Importantly, biocrusts growing in the runon areas were taller, had shorter rhizines, and a greater capacity to trap sediment and absorb water. There were no effects of grazing intensity nor herbivore type (sheep cf. kangaroo) on any diversity or functional measures of biocrusts. Overall, our study indicates that the functional attributes of biocrusts align with those reported for vascular plants (e.g., perennial grasses), by affecting hydrological processes and sediment capture, albeit at smaller spatial scales. Biocrusts may be important, therefore, for sequestering small falls of water emanating from resource-shedding zones, thereby reinforcing landscape patchiness, particularly as hotter and drier climates reduce the cover of vascular plants in drylands. [ABSTRACT FROM AUTHOR]

• In urban environments soil connectivity is the principal condition to achieve soil security. • Soil-society relationships are implicated in the development of urbanism. • Spatial design, soil formation, and soil care in Maya urbanism reveal soil connectivity. • Soil connectivity in Maya urban life is promoted by encountering and engaging with soils. • Archaeological insights on soil connectivity can benefit planning for urban sustainability. Soils are a pivot of sustainable development. Yet, urban planning decisions persist in compromising the usability of the urban soils resource. Urban land cover expansion to accommodate an increasing population results in soil sealing. Concealment of and physical obstructions to soils prevent urban populations from engaging with their soil dependency. The concept of soil connectivity recognises that nurturing mutually beneficial soil–society relations is an essential dimension for achieving soil security. The concentrated populations of urban environments acutely require productive soil–society relations and offer the greatest potential for enhancing soil connectivity. Soil connectivity remains notably under-researched, however, resulting in deficient evidence to substantiate exactly how soil connectivity can contribute to sustaining urban life. The entanglement of soil and urban development has been critical throughout history, but seldom recognised in soil security discourse. We review the manifestation of effective soil connectivity in Precolumbian lowland Maya tropical urbanism. Archaeological evidence reveals, first, that lowland Maya urban settlement patterns largely preserved the availability, proximity, and accessibility of soils in the subdivision and configuration of urban open space. Second, Maya urban life included practices that proactively contributed to the formation of soils by adding to the stock of soils and improving beneficial soil properties of the thin and often nutrient-poor soils resulting from the regionally dominant karstic lithology. Third, a range of Maya landscape modifications and engineering practices enabled the preservation and protection of soils within urban environments. We derive evidence-based insights on an urban tradition that endured for well over two millennia by incorporating intensive soil–society relationships to substantiate the concept of soil connectivity. Inspiring urban planning to stimulate soil connectivity through enhancing the engagement with soils in urban life would promote soil security. [ABSTRACT FROM AUTHOR]

• Reduction of soil strength by cover crops was not consistent within the year. • On an annual base cover crops affected soil strength by modifying soil water content. • Barley mulch increased water content, thus reducing soil strength before maize sowing. • The grass barley cover crop reduced soil strength more than legume vetch. • A combination of cover crops and reduced tillage diminished the risk of soil crusting. Replacement of bare fallow in rotations by cover crops is a promising tool to reduce crusting, although the interactions with the soil moisture and the effect of the cover crop species are still not well understood. The objective of this work was to determine how cover crops modify the soil surface response to penetration and their relation with the soil water content. Two winter cover crops, barley (Hordeum vulgare L.) and vetch (Vicia sp. L.), were compared with a bare fallow treatment in a 10-year field experiment in central Spain. Soil resistance to penetration and soil water content were intensively measured (76 sampling dates) at two surface depths, using two types of surface penetrometers. Under the barley cover crop, the number of very dry events was reduced by around 20%, compared to the bare fallow. The soil resistance to penetration was closely related to the surface soil water content (R2 = 0.65) and cover crops affected it through soil moisture modification. In this line, the greater mulch provided by barley cover crop respect to vetch, increased the soil water content prior to main crop seeding, resulting in less resistance to penetration during this critical period. The good performance of barley resulted in a reduction of more than 60% of the soil resistance to penetration between the 3rd and 8th year of the experiment (7.2–2.9 kg cm−2, respectively). Even under bare fallow, soil strength was decreased after ten years with reduced tillage. Therefore, the maintenance of cover crop residues over surface soil together with reduced tillage enhanced the soil surface conditions and steadily reduced the risk of crust formation. Expected enhancement of main-crop germination, water infiltration, soil aeration and erosion mitigation may be attained by cover-cropping in degraded soils. [ABSTRACT FROM AUTHOR]

• Field trials on the use of MICP for wind erosion control of desert soil are conducted. • Soil crusts on loose cohesionless desert soil exist after MICP treatment. • MICP shows pleasurable ecological compatibility and long-term sustainability. • MICP is a promising candidate to mitigate wind erosion of desert soils in drylands. This study examined the potential of microbially induced carbonate precipitation (MICP) in reducing wind erosion of desert soil. Field tests were conducted on artificial mounds and bare sandy land located in Ulan Buh Desert, Ningxia Hui Autonomous Region, China. Results showed that the MICP method could significantly enhance the bearing capacity and wind erosion resistance of the surficial soil through the formation of soil crusts. The optimal cementation solution (containing equimolar urea and calcium chloride) concentration and spraying volume, were 0.2 M and 4 L/m2, respectively. Under this condition, the soil crusts, with a thickness of 12.5 mm and a calcium carbonate (CaCO 3) content of 0.57%, remained intact on the surface of man-made mounds after being exposed to a 30 m/s wind for 2 min. For the sandy land, the soil bearing capacity could reach its maximum of 459.9 kPa (as measured with a 6 mm-diameter handheld penetrometer) within three days, and the depth of wind erosion was approximately zero after 30 days of exposure to the local weather conditions. Furthermore, the biocementation method showed its ecological compatibility at the optimal dosage. Scanning electron microscopy (SEM) tests with energy dispersive X-ray (EDX) confirmed the bridge effect of CaCO 3 crystals. Longer-term durability of MICP treatment was evaluated, and the results showed that soil bearing capacity and wind erosion resistance of the sandy land was significantly improved over 180 days. These findings suggest that MICP is a promising candidate to protect desert soils from wind erosion. [ABSTRACT FROM AUTHOR]

• Litter coverage accelerates biocrusts' decomposition in sandy ecosystems. • Litter-covered biocrusts can further improve topsoil nutrients and microhabitats. • Sandy soil fractal dimension (D) significantly increased with litter cover. • Litter cover promotes the transformation of sandy to loamy textures. Ecological restoration of sandy inland ecosystems is important for achieving global sustainability. In the world's semi-arid regions, soil crusts play crucial roles in maintaining ecosystem functioning. However, the true extent of soil quality improvement during the development of crusts is an issue not solved. In this study, four development stages of natural soil crusts, i.e., physical crusts (PC), biocrusts (BC), litter covered biocrusts (LBC) and litter crusts (LC) were selected in a semi-arid sandy ecosystem, along with a bare sandy land (BSL) as control area, to evaluate soil physicochemical properties at different soil depths. The coverage of litter (mainly leaves of Populus simonii) increased soil moisture and reduced soil bulk density. Compared with BC, the content of total soil organic matter (SOM) decreased in LBC by 13.83% and increased in LC by 36.57%. In contrast with BC, LC promoted a significant increase in soil nutrients, such as total nitrogen (30.30%), total phosphorus (46.89%) and available potassium (34.40%) in the topsoil layer (0–2 cm). Besides, LC contained higher clay and silt contents (10.47% and 29.81%) and lower sand content (−1.02%) than BC. In the 0–10 cm soil layer, the D (fractal dimension of the soil particle size distribution) of LC was the largest, with a value 5.71%, 6.1%, 2.44% and 0.93% higher than D in BSL, PC, BC and LBC, respectively. These findings reveal that litter covering facilitate the disintegration of BC, which further forms LC, and these processes clearly promote the enhancement of soil quality under sandy semi-arid conditions. Our findings are particularly important for predicting the transformation processes of sandy soil crusts and are of interest in ecological restoration programs. [ABSTRACT FROM AUTHOR]

• Seabirds and semiaquatic marine mammals affect coastal soils in a similar way. • They deposit the byproducts in the soil and cause soil erosion. • Soils affected by mammals have a significantly higher content of C, N, P, and S. • Such soils contain a lot of hair and can be easily identified in the field. • The Mammalic qualifier in the WRB is needed to identify soils affected by mammals. [ABSTRACT FROM AUTHOR]

• Three stages of soil development are proposed based on sugars distribution. • During the first stage sucrose dominates. • Arabitol, mannitol and trehalose increase during II stage of soil development. • In stage III the contents of pinitol and myo -inositol considerable increase. • The relationships between sugars and TOC differentiated the soil crust development. Saccharides are common constituents of soils, but their role and origin in the initial phases of pedogenesis remain unclear. Here we show the detailed composition of neutral sugars extracted from arenosols at different development stages, combined with additional lipids of diverse origins using gas chromatography-mass spectrometry (GC–MS). During the first stage (I) of development sucrose is the most abundant saccharide in the soil crust at up to 45,000 µg/g TOC. Sucrose is also the predominant compound in the second and third development stages, but its concentration decreased to the range of 1600 to 16,000 µg/g TOC. Stages II and III of soil development were characterized by a gradual increase in arabitol, mannitol and trehalose, compounds typical for fungi and lichen. Their abundances increased from several percent (compared to the major sucrose) to 10–32% for mannitol and 34–54% for trehalose. Moreover, in stage III there was a considerable increase in the contents of the saccharides: pinitol, myo -inositol, scyllo -inositol, arabinose, together with non-sugar compounds: dehydroabietic acid, p -hydroxybenzoic acid, gallic acid and sitosterol. All these latter compounds are higher plant markers, mainly derived from conifer detritus. The relationships between the ratios of trehalose/sucrose vs. (mannitol + arabitol)/sucrose and TOC vs. (mannitol + arabitol)/sucrose differentiated precisely the top soil layer of arenosols which are covered by different stages of biological soil crust. Our study shows that free sugars, supplemented by lipid biomarkers and total organic carbon contents, are good indicators of soil in the initial phase of pedogenesis. [ABSTRACT FROM AUTHOR]