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The changes of soil moisture, salinity, and nutrients by halophyte colonization in high-salinity environment profoundly affect the assembly and structure of microbial communities. However, salt marshes in arid region have received little attention. This study was conducted in Lianhuachi Lake, a typical inland salt marsh wetland in China, to determine the physicochemical characteristics of salt crusts in [Kalidium cuspidatum (Ung.-Sternb.) Grub.] colonization areas and bulk soil, respectively, and to analyze the microbial community structure of salt crusts by high-throughput sequencing. Kalidium cuspidatum colonization significantly decreased total salinity, soil water content, and water-soluble ions of salt crusts and increased total carbon, total nitrogen, and total phosphorus content. At the same time, changes in physicochemical properties caused by Kalidium cuspidatum colonization affect the ecological processes of bacterial, fungal, and archaeal community assemblies in salt crusts. In addition, cross-kingdom network analysis showed that Kalidium cuspidatum colonization increased the complexity and stability of microbial networks in salt crust soils. Functional projections further showed that bacterial diversity had a potential driving effect on the nitrogen cycle function of salt crust. Our study further demonstrated the different ecological strategies of microorganisms for halophyte colonization in extreme environments and contributed to the understanding of restoration and management of salt marsh wetlands in arid region. [ABSTRACT FROM AUTHOR]

As important components of the biological soil crusts (BSCs) and of the primary stage of crust succession, cyanobacterial communities occupy an important ecological niche and play an important ecological role in desertification areas. In this study, we focused on the karst desertification area, which also belongs to the same category of desertification, and selected three study areas, Guanling-Zhenfeng Huajiang (HJ), Bijie Salaxi (SLX), and Shibing (SB), in the Guizhou Plateau, which represents the overall ecological environment of South China karst, to conduct surveys on the diversity of BSC species and soil properties. Analysis of the cyanobacterial communities and physicochemical properties using the Shannon-Wiener diversity index, principal component analysis, and redundancy analysis revealed that: (1) The three study areas had common cyanobacterial species, with a total of 200 species distributed across 22 genera, 2 classes, 5 orders, and 6 families belonging to the Oscillatoriales (39%), Scytonematales (24.5%), Chroococcales (23%), Nostocales (11.5%), and Rivulariales (2%), (2) The number of species increased with the intensity of karst desertification--while Oscillatoriaceae was the dominant family in HJ and moderate-severe desertification areas, Chroococcaceae and Scytonemataceae were dominant in the mild and potential desertification areas SLX and SB, (3) The Shannon-Wiener diversity indices followed the trend: SLX (3.56) > SB (3.08) > HJ (3.01), indicating that the species were more evenly distributed in mild desertification, (4) In the carbonate background, shrubland harbored the largest number of cyanobacterial species compared to grassland, bare land, and arbor woodland; however, the highest number was documented in arbor woodland in dolomite karst, (5) The soil is weathered limestone or yellow soil in all three areas, with pH ranging from 5.73 to 6.85, fine sand dominated, and soil nutrients increased with the intensity of desertification, and (6) Redundancy analysis showed that organic carbon, soil moisture content (0-5 cm), and total nitrogen substantially influenced cyanobacterial diversity. These results reveal that differences in soil nutrient content play an important role in regulating the cyanobacterial diversity and composition, thereby establishing a foundation for further research and application of soil ecological restoration of cyanobacteria in BSCs of karst desertification areas. [ABSTRACT FROM AUTHOR]

Dry salt lakes are widely distributed in semi-arid regions. Dry lake beds have been found to have a greater capacity to release dust. However, the particle size characteristics of dry lakebed soils have rarely been studied. To reveal the soil grain size characteristics, we used surface and subsurface soil from dry lake beds in semi-arid regions with different soil crusts as the object of study. We used particle size parameters and class-standard deviation methods to study the particle size variation patterns and the degree of variability. The results show that the dry lake was mainly composed of clay (1.36%-43.96%) and silt (5.5%-67.94%) particles. Soil particle characteristics show the Mean size (Mz) of (0.65-8.89 f), poorly sorted (0.79-3.38 f) and a clear linear relationship between dry lake bed skewness and sorting. There is a high variability between soil particle size fractions across the lake bed, with soil crusts and soil moisture protecting the loss of subsurface soil particles, hence the differences between surface and subsurface soil particles. However, the destruction of the soil crust and the evaporation of soil moisture accelerates the wind erosion of the subsurface soil particles. In the dry lake area, vegetation construction has promoted the accumulation of sand content (73.28% -93.08%). We found that the fractions 0.19-9.15 µm, 9.15-36.99 µm, 36.99-366.93 µm, and 366.93-1214.72 µm are susceptible to respond to environmental changes and contribute to dust storms. Therefore, local governments should treat and manage dried-up lakes to reduce the impact of salt dust on the ecosystem. [ABSTRACT FROM AUTHOR]

Geochemical background is the basis of anomaly evaluation in mineral exploration and environmental investigation. However, the background value obtained from secondary media is inevitably affected by weathering, transportation, and sorting, which leads to secondary depletion or enrichment of chemical elements. This problem can be avoided by the geochemical mapping of the exposed crust. In this paper, more than 38,000 samples of rocks data were collected, and an original method was presented for the first time to produce the cobalt geochemical map of exposed crust across the whole of China. Using a geological map grid of 1:200,000 as the basic calculation unit, the area and content of rock types in each unit were calculated, and then the grid was assigned using the area-weighted average method. Based on this, an geochemical contour map was drawn in ArcGIS. The results show that the median of the exposed crust is 9.74 mg/kg, which is lower than that of the whole crust and soils. This value is explained by the vertical heterogeneity of the crust and the secondary enrichment, respectively. Co anomalies and anomalous centers of exposed crust are distributed in southwest, north, and northwest China, where they are primarily related to Permian Emeishan Large Igneous Province (ELIP), Pacific plate, and the big mantle wedge (BMW), Archean metamorphic basic rocks, and ophiolite belts. [ABSTRACT FROM AUTHOR]

Accurate assessments of soil organic carbon (SOC) storage beneath impervious surface areas (ISAs, SOCISA) are key for understanding the urbanization impact on carbon pools, but previous studies either ignored the SOCISA pool or overlooked the urbanization impacts on the SOC pool. Based on observations from 152 sampling sites in 43 cities, we show that mainland China has a SOCISA stock of 1,016 Tg to 100‐cm depth, with a mean density of 6.21 ± 3.90 kg m−2. Comparison between SOCISA and the SOC of background soil (SOCbackground) indicates ∼19% SOC loss due to ISA conversion, similar to the effect of cropland conversion. Unlike the vertical pattern of SOCbackground, which declined faster in the upper soil layers, SOCISA decreased linearly with depth. Moreover, the SOCISA is uncorrelated with SOCbackground and decreases with precipitation. These unique patterns indicate the SOC loss mainly caused by topsoil removal during land conversion. The fact that the SOCISA of older ISA was not lower than that of newly converted ISA further confirmed that soil sealing preserved SOC. Finally, both the high correlation between SOCISA and SOCPSA (SOC of the adjacent pervious surfaces) and the converging SOC densities in urban soils showed strong influences from urban greenspace on SOCISA. Based on the findings, we recommend improving greenspace management to increase the presealing SOC stock, preventing ISA construction in wet/warm seasons to mitigate SOC loss, and developing technology to seal carbon stock under ISA. We conclude that SOCISA is a major component of the urban carbon pool. It has a unique spatial pattern and cannot be estimated using surrogate data such as SOCbackground or SOCPSA. Plain Language Summary: Rapid urbanization all over the world could cause severe loss of soil organic carbon (SOC) which is the major part global carbon stock. However, due to the paucity of field observations, we still have no idea of the size and distribution pattern of the SOC pool (SOCISA) under the impervious surface areas (ISAs). This knowledge gap limits our ability to assess the impacts of urbanization on carbon balance. Based on observations from 152 sampling sites in 43 cities, here we show China has a SOCISA stock of 1,037 Tg to 100‐cm depth, with mean density of 6.21 ± 3.90 kg m−2, much higher than most previous estimations. Unlike the vertical pattern of rural SOC which declines faster in the upper soil layers, SOCISA decreases linearly with depth. The spatial distribution of SOCISA is negatively correlated to urbanization rate and precipitation, different from the general pattern of China's SOC which increased with precipitation. ISA expansion may cause 19% SOC loss, and the loss in the South is much severe than the North. The unique pattern indicates soil carbon pool mainly losses during urban land conversion but is preserved after soil sealing. Key Points: The observed soil organic carbon (SOC) density under impervious surfaces is much higher than previous assumptionsAn average 19% SOC loss, mainly due to impervious surface constructionThe SOC density of impervious surfaces decreases with precipitation but is uncorrelated with the background SOC [ABSTRACT FROM AUTHOR]

K17, an indigenous and heterotrophic nitrifying-aerobic denitrifying bacterium, was isolated from the soil of a weathered crust elution-deposited rare earth ore leaching site in Longnan County, China. Strain K17 was identified as Pseudomonas mosselii. In this study, the morphological characteristics of strain K17 were observed and the optimal ammonia nitrogen removal conditions for the strain were studied using a single-factor experiment. Key enzyme activities were determined, and we also explored the ammonia nitrogen removal process of strain K17 on simulated leaching liquor of the rare earth element leaching site. Based on the determination of ammonia nitrogen removal and enzyme activity, it was found that strain K17 has both heterotrophic nitrifying and aerobic denitrifying activities. In addition, single-factor experiments revealed that the most appropriate carbon source for strain K17 was sodium citrate with a C/N ratio of 10 and an initial NH4+-N concentration of 100 mg/l. Furthermore, the optimal initial pH and rotation speed were 7 and 165 r/min, respectively. Under optimal conditions, the ammonia nitrogen removal efficiency of strain K17 was greater than 95%. As an indigenous bacterium, strain K17 has great potential for treating residual ammonium leaching solutions from rare earth element leaching sites. [ABSTRACT FROM AUTHOR]

Objective: The plant canopy, plant roots, and biological soil crusts play important roles in soil detachment by overland flow. This study aims to quantify and analyze the effects of the plant canopy, plant roots, and soil crust on soil detachment via in situ experiments. Materials and methods: Two typical dominant species, Bothriochloa ischaemum (Linn.) Keng (an herb) and Sophora davidii (Franch.) Skeel (a shrub) on the Loess Plateau, China, were selected. Four treatments were denoted T0 (bare land), T1 (canopy + root + crust), T2 (root + crust), and T3 (root) and subjected to flow scouring with a discharge of 5 L min−1 on a 20° slope. Results and discussion: The soil detachment rate (SDr) in all treatments decreased sharply in the first 3 min due to changes in the internal force of the soil particles. As the effects of the canopy, roots, and soil crust were subsequently superimposed, the SDr decreased by 87.42–93.42% compared with that of the bare land. The plant canopy, roots, and soil crust contributed 8.57–9.54%, 92.36–95.27%, and −1.90 to −3.84% of the soil detachment reduction (SDR), respectively. Additionally, the naturally restored herb roots decreased soil detachment by flowing water more significantly than shrub roots in the study area. Conclusions: The effects of canopy, roots, and soil crust on SDr in grassland were similar to those in shrubland. Roots played a crucial role in strengthening soil resistance to detachment. Although shrubland had a greater effect on soil detachment reduction than grassland, herbs are strongly recommended for reducing soil erodibility due to the greater erosion-reducing potential of roots and their drought resistance on the Loess Plateau. [ABSTRACT FROM AUTHOR]

In north-west China, extensive areas of gravel desert exist, whose surface properties have an important effect on the wind-erosion threshold friction velocity u ∗ t . In this study, we use four models and field observations of gravel mass fraction, soil physical crust, and soil clay content to assess the effect of gravel-surface properties on the value of u ∗ t . Results show that gravel coverage in north-west China ranges between 0.07 and 1.00 (with a mean of 0.67), and about 81% of the sites investigated are covered by soil physical crust. Clay content is 2.4% on average in the study region, less than 2% in 52.1% of that region, and between 2 and 4% in the remaining study regions. The four regions where clay content is greater than the mean include the western Alxa Plain, the alluvial fan of the western Alxa Plain, the northern Alxa Plain, and the Hexi Corridor. In the study region, the value of u ∗ t ranges between 0.12 and 0.78 m s−1 (with a mean of 0.45 m s−1). Soil moisture, gravel coverage, and soil physical crust all affect the magnitude of u ∗ t . A principal component analysis indicates that the soil crust contributes of about 62% of the u ∗ t variations, soil moisture 25%, and surface roughness 9%. A variance analysis shows clear spatial differences in the magnitude of u ∗ t in north-west China due to the spatial variations in gravel land-surface properties. [ABSTRACT FROM AUTHOR]

In recent years, inoculating sand surfaces with biocrust organisms has become one of the most promising biotechnological strategies for controlling and reversing land degradation in drylands. To fully exploit this biotechnology on a large scale in drylands, researchers must explore water‐saving techniques to incubate biocrusts in situ. To achieve this aim, we tested three methods—broadcasting dried cyanobacteria, spraying fresh cyanobacteria, and broadcasting natural biocrust fragments—to culture biocrusts in situ on the Tengger Desert in Northern China. The cover of incubated biocrust increased during the first 2 months after inoculation (from 6% to more than 20.0% in treatments using biocrust fragments); biocrust cover declined but persisted after 12 months of incubation (13.8% cover in the best treatment, natural cyanobacteria fragments). The cover of cyanobacteria was higher than the cover of lichen in our natural cyanobacteria‐lichen crust fragment treatment (NCL; p <.05) after incubating for 12 months. We highlight that cyanobacteria should be selected for biocrust incubation during the initial stages of dryland restoration. Accumulated rainfall was positively related to the cover of incubated biocrust. However, wind speed and wind erosion intensity were both negatively related to the cover of incubated biocrust. In conclusion, broadcasting biocrust fragments is a rapid, efficient, and water‐saving biotechnique to cultivate biocrusts in situ. Actions to reduce wind speed and wind erosion, such as mechanical sand fixing, can help stabilize soils and improve crust cultivation. [ABSTRACT FROM AUTHOR]

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]

The response of runoff and erosion to soil crusts has been extensively investigated in recent decades. However, there have been few attempts to look at the effects of spatial configuration of different soil crusts on erosion processes. Here we investigated the effects of different spatial distributions of physical soil crusts on runoff and erosion in the semi-arid Loess Plateau region. Soil boxes (1.5 m long × 0.2 m wide) were set to a slope of 17.6% (10°) and simulated rainfall of 120 mm h−1 (60 minutes). The runoff generation and erosion rates were determined for three crust area ratios (depositional crust for 20%, 33%, and 50% of the total slope) and five spatial distribution patterns (depositional crust on the lower, lower-middle, middle, mid-upper, and upper slope) of soil crusts. The reduction in sediment loss ('sediment reduction') was calculated to evaluate the effects of different spatial distributions of soil crusts on erosion. Sediment yield was influenced by the area ratio and spatial position of different soil crusts. The runoff rate reached a steady state after an initial trend of unsteadily increasing with increasing rainfall duration. Sediment yield was controlled by detachment limitation and then transport limitation under rainfall. The shifting time of erosion from a transport to detachment-limiting regime decreased with increasing area of depositional crust. No significant differences were observed in the total runoff among treatments, while the total sediment yield varied under different spatial distributions. At the same area ratio, total sediment yield was the largest when the depositional crust was on the upper slope, and it was smallest when the crust was deposited on the lower slope. The sediment reduction of structural crust (42.5-66.5%) was greater than that of depositional crust (16.7-34.3%). These results provide a mechanistic understanding of how different spatial distributions of soil crusts affect runoff and sediment production. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Soil erosion and subsequent land degradation contributed to societal collapse in the past and are a leading cause of desertification in arid and semi-arid regions. Biological soil crusts (biocrusts) are ubiquitous living covers in many arid and semiarid ecosystems that have an important role in soil stabilization and erosion prevention. The “Grain for Green” ecological project improved vegetation recovery, and led to an extensive development of biocrusts across the Loess Plateau region in China, one of the most eroded regions in the world. The expansion of biocrusts was instrumental in reducing soil loss in a very large, severely eroded region of the Loess Plateau. We hypothesized that development of biocrusts would change soil organic matter (SOM) and soil particle size distribution (PSD), thereby reducing soil erodibility and soil loss. We sampled 56 sites that were passively revegetated grasslands on former croplands and 3 bare soil sites in the Loess Plateau region, and used the erosion productivity impact calculator (EPIC) model combined with simulated rainfall to test our assumption. The PSD and SOM content varied significantly among biocrust types and successional stages. The SOM content was 4 times higher in moss dominated biocrust and 1.5 times greater in cyanobacterially dominated biocrust than bare soil. More fine-particles (< 0.01 mm) and fewer coarse-particles (0.05–0.25 mm) were present in biocrusts than in bare soil. Modeled soil erodibility decreased significantly as biocrust biomass increased, mainly due to increase in SOM content, reducing the predicted soil loss by up to 90%. Finally, the prevalence of moss biocrust was a better predictor of soil erodibility than cyanobacteria in the Loess Plateau region. We conclude that biocrusts were a decisive factor for the initial reduction of soil erosion, which must be considered explicitly in models that aim to predict and manage soil loss on the Loess Plateau. [ABSTRACT FROM AUTHOR]

• BSCs is superior to the vascular vegetation in degraded meadow patches, especially restoring LOC, TN and SOM in soil. • Altitude and soil depth significantly reduced the content of LOC in soil. • BSCs promote the restoration of soil LOC by increasing soil TN content. Biological soil crusts (BSCs) play an important ecological role in the biogeochemical cycles, but there is limited knowledge about their effects on the composition of soil labile organic carbon (LOC) in the soil of patchy alpine meadow. In patchy alpine meadow with different altitudes, the different LOC compartments, vegetation, soil properties and C-hydrolase activity of active patches (with plateau pika), inactive patches (without plateau pika), restored patches, BSCs patches, and healthy alpine meadow were analyzed to assess the effects of BSCs on LOC. The key influence pathway of eco-environmental factors of LOC was determined by the structural equation model (SEM). The results showed that the BSCs at the altitude of 3570 m increased dissolved organic carbon (DOC), easily oxidized organic carbon (EOC) and microbial carbon (MBC) by 293%, 73% and 36%, respectively, compared with active patches in the 0–2 cm layer, which was significantly higher than those of inactive patches and recovered patches. There was no significant difference among DOC, EOC and MBC in different patches at the altitude of 4224 m. The MBC content of active patches decreased, but other patches and healthy alpine meadow showed a Λ- shaped change with altitude. The contents of soil total nitrogen and organic matter of BSCs patches were generally higher than those of active and inactive patches at three different altitudes. Structural equation model results showed that at the altitude of 3570 m, total nitrogen had a strong positive correlation with DOC, with a path coefficient of 0.677. There was a direct negative relationship between soil organic matter and DOC (path coefficient = −0.278) at the altitude of 4013 m. At the altitude of 4224 m, there was no direct correlation among soil nutrient, C-hydrolase activity, and soil LOC. Therefore, BSCs mainly promote the accumulation and recovery of LOC by increasing the soil total nitrogen content in different patches at different altitudes, which are beneficial to the restorations of LOC, total nitrogen and soil organic matter. Hence, they should be considered as key factors in the processes of restoring patchy alpine meadows. [ABSTRACT FROM AUTHOR]

Soil sealing (loss of soil resources due to extensive land covering for the purpose of house building, road construction etc.) and subsequent soil landscape pattern changes constitute typical environmental problems in many places worldwide. Previous studies concentrated on soil sealing in urbanized regions, whereas rural areas have not been given sufficient attention. Accordingly, this paper studies soil landscape pattern dynamics (i.e., landscape pattern changes in response to rural anthropogenic activities) in the Tiaoxi watershed (Zhejiang province, eastern China), in which surface sealing is by far the predominant component of human forcing with respect to environmental change. A novel approach of quantifying the impacts of rural anthropogenic activities on soil resources is presented. Specifically, quantitative relationships were derived between five soil landscape pattern metrics (patch density, edge density, shape index, Shannon’s diversity index and aggregation index) and three rural anthropogenic activity indicators (anthropogenic activity intensity, distance to towns, and distance to roads) at two landscape block scales (3 and 5 km) between 1985 and 2010. The results showed that the Tiaoxi watershed experienced extensive rural settlement expansion and high rates of soil sealing. Soil landscapes became more fragmented, more irregular, more isolated, and less diverse. Relationships between soil landscape pattern changes and rural anthropogenic activities differed with the scale (spatial and temporal) and variable considered. In particular, the anthropogenic activity intensity was found to be the most important indicator explaining social development intensity, whereas the other two proximity indicators had a significant impact at certain temporal interval. In combination with scale effects, spatial dependency (correlation) was shown to play a key role that should be carefully taken into consideration in any relevant environmental study. Overall, the findings of this work suggest that soil sealing can be a critical human forcing issue with considerable consequences deserving serious attention by the experts, the public and the government alike. [ABSTRACT FROM AUTHOR]

The South China Block, composed of the Yangtze and Cathaysia sub-blocks which were sutured along the Jiangnan Orogen, preserves the records of multiple tectonothermal and metallogenic events coeval with global supercontinental cycles. In this study, we attempt to evaluate the mantle dynamics in this region based on P-wave tomographic analyses from data recorded by the China seismic network from 2007 to 2014. Our study reveals significant velocity perturbations in the upper mantle and mantle transition zone beneath this region which we correlate with various features including remnant and stagnant slabs resulting from Neoproterozoic subduction events and prominent mantle upwellings. Four vertical cross-sections along the latitudinal profiles indicate significant low velocity perturbation located at the mantle transition zone and upper mantle beneath the Cathaysia block and Jiangnan orogenic belt. South China is one of the major multi-metal provinces of the globe, and carries several large-scale ore deposits associated with a variety of tectonic settings. The distribution of major mineral deposits in the Yangtze and Cathaysia blocks as well as along the Jiangnan Orogen reveals a remarkable correlation between the location of the deposits and deep-seated low velocity P-wave anomalies. These features highlight the role of mantle dynamics and resultant crust mantle-interaction as well as crustal melting and recycling in generating the major metallogenic belts in this region. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) are common and play critical roles in semi-arid and arid ecosystems. Bacteria, as an important community in BSCs, play critical roles in biochemical processes. However, how bacterial diversity and community change in different successional stages of BSCs is still unknown. We used 454 pyrosequencing of 16S rRNA to investigate the bacterial composition and community, and the relationships between bacterial composition and environmental factors were also explored. In different successional stages of BSCs, the number of bacteria operational taxonomic units (OTUs) detected in each sample ranged from 2572 to 3157. Proteobacteria, Cyanobacteria, Bacteroidetes were dominant in BSCs, followed by Firmicutes, Acidobacteria, and Actinobacteria. At the successional stages of BSCs, bacterial communities, OTU composition and their relative abundance notably differentiated, and Cyanobacteria, especially Microcoleus vaginatus, dominated algal crust and lichen crust, and were the main C-fixing bacteria in BSCs. Proteobacteria and Bacteroidetes increased with the development of BSCs. OTUs related to Planomicrobium Chinese, Desulfobulbus sp., Desulfomicrobium sp., Arthrobacter sp., and Ahhaerbacter sp. showed higher relative abundance in bare sand than other successional stages of BSCs, while relative abundance of Sphingomonas sp. Niastella sp., Pedobacter, Candidatus solobacter, and Streptophyta increased with the development of BSCs. In successional stages of BSCs, bacterial OTUs composition demonstrated strong correlations with soil nutrients, soil salts, and soil enzymes. Additionally, variation of bacterial composition led to different ecological function. In bare sand, some species were related with mineral metabolism or promoting plant growth, and in algal crust and lichen crust, C-fixing bacteria increased and accumulated C to the desert soil. In later developed stage of BSCs, bacteria related with decomposition of organic matter, such as Sphingomonas sp. Niastella sp., Pedobacter, and Candidatus solobacter increased. Therefore, bacterial community composition and their key ecological roles shifted to the development of BSCs. [ABSTRACT FROM AUTHOR]

• Structural and depositional crusts have variable particle size distribution (PSD). • PSD is measured under different rainfall durations to determine soil erodibility. • The formation mode and PSD of physical crust depend on micro terrain and rainfall. • Rainfall and tillage result in heterogeneous PSD and erodibility. • Significant correlations are found between erodibility and multifractal parameters. Understanding the knowledge of multifractal analysis on particle size distribution (PSD) of soil physical crusts is indispensable for progressing soil surface erosion mode. In this study, hoeing tillage (20 cm long × 15 cm wide × 5 cm deep) were conducted to simulate classic tillage mode in Yangling, China to obtain physical crusts under artificial rainfall (60 mm h−1 intensity with three durations (5, 15, and 30 min)). We defined crusts formed in ridges as structural crust (C st), formed by infiltration of runoff in hoes as sediment-containing depositional crust (C scd), and formed by the extraction of runoff as sediment-free depositional crust (C sfd). Soil stratification methods were used to explore physical crust particle sorting. Results represented that the sand content of C st , C scd , and C sfd decreased, whereas clay and silt contents increased after rainfall compared to undisturbed soil. There was no significant difference between C scd and C sfd under short rainfall duration. Three crust types became gradually concentrated in areas with higher density with increasing rainfall duration according to six common parameters in the generalised dimension spectrum (D 0 , D 1 , D 2 , D 1 / D 0 , D v (D -10 – D 0), and D s (D 0 – D 10)). Multifractal singularity spectrum (α 0 , A v , F v) showed that PSD was most symmetrical in C sfd , followed by C scd and C st. Erodibility index K EPIC was largest for C st , followed by C sfd then C scd. The relationship between K EPIC and multifractal parameters were significant. Spatial difference caused by tillage activities and rainfall events determine the heterogeneous formation mode, particle size distribution and erodibility of physical crust. [ABSTRACT FROM AUTHOR]

In almost all dryland systems, biological soil crusts (biocrusts) coexist alongside herbaceous and woody vegetation, creating landscape mosaics of vegetated and biocrusted patches. Results from past studies on the interaction between biocrusts and vascular plants have been contradictory. In the Gurbantunggut desert, a large temperate desert in northwestern China, well-developed lichen-dominated crusts dominate the areas at the base and between the sand dunes. We examined the influence of these lichen-dominated biocrusts on the germination, growth, biomass accumulation, and elemental content of five common plants in this desert: two shrubs ( Haloxylon persicum, Ephedra distachya) and three herbaceous plants ( Ceratocarpus arenarius, Malcolmia africana and Lappula semiglabra) under greenhouse conditions. The influence of biocrusts on seed germination was species-specific. Biocrusts did not affect percent germination in plants with smooth seeds, but inhibited germination of seeds with appendages that reduced or eliminated contact with the soil surface or prevented seeds from slipping into soil cracks. Once seeds had germinated, biocrusts had different influences on growth of shrub and herbaceous plants. The presence of biocrusts increased concentrations of nitrogen but did not affect phosphorus or potassium in tissue of all tested species, while the uptake of the other tested nutrients was species-specific. Our study showed that biocrusts can serve as a biological filter during seed germination and also can influence growth and elemental uptake. Therefore, they may be an important trigger for determining desert plant diversity and community composition in deserts. [ABSTRACT FROM AUTHOR]

The objective of this laboratory study was to assess the effects of soil crusts and tillage treatments on soil erosion in the Loess Plateau of China. The simulated rainfall storms at 40 mm/h, 60 mm/h and 80 mm/h rates were applied to the soil boxes set to a 17.6% slope, two soil surface conditions (crusted and uncrusted soil surface) and two tillage types (contour tillage and straight slope) were used to investigate the resulting runoff rate and sediment yield. Results show that the runoff rates were greater and total soil loss was lower in crusted than uncrusted soils. Contour tillage treatment resulted in smaller runoff rate and total soil loss than straight slope treatment. Rainfall intensity, soil crusts and tillage treatments had very significant (p < 0.001) effects both on total runoff yield and soil loss. The combined effects of rainfall intensity and tillage treatment on total runoff yield and soil loss were much more significant (p < 0.01) than the other combined effects (p < 0.05). Rainfall intensity had a greatest correlation with the total runoff yield while tillage treatments had a greatest correlation with the total soil loss. As a result, the tillage treatments in the Loess Plateau can reduce the impact of soil crusts on soil erosion effectively. [ABSTRACT FROM AUTHOR]

Soil crusts commonly form in arid and semi-arid desert regions once shifting sand dunes stabilize. The crusts affect soil properties such as texture and fertility. However, the role of crusts depends on the species composition, their physiological activity, and their stage of evolution, and varies with precipitation and season. In this study, the soil properties of physical and biological crusts in different rainfall zones of the arid and semi-arid desert regions of northern China were analyzed. More developed crusts had finer soil texture. The impact on chemical properties was greater in areas with higher precipitation. Contents of soil organic carbon (SOC), total nutrients, available N, and exchangeable ions did not vary among crust types in a hyperarid region. SOC, total N and P, and available N increased with crust development at 150-400 mm rainfall. Soil crusts increased available P during the initial stage of development. Crust development increased available K at 300-400 mm precipitation, but not at ≤250 mm precipitation. CaCO changes were related to windblown dust and soil moisture in the crust. Electrical conductivity and total salinity varied in response to variation of soil nutrients and aeolian salt accumulation. The pH did not vary greatly between crust types and sites. Crust development was accompanied by soil alkalization. Ca was more abundant than other cations. Crust development did not influence Cl, but increased HCO and Na. During crust development, SO and K contents decreased, and Mg increased, in regions with ≤250 mm precipitation. The opposite changes occurred at 300-400 mm precipitation. [ABSTRACT FROM AUTHOR]

• Plant litter incorporated in soil has great effects on inhibiting soil detachment process. • Litter incorporation affects the temporal variation in soil detachment capacity through changing soil structure by physical binding and chemical secretion. • Plant litter incorporated in soil can promote the formation of physical soil crust. • Flow shear stress and soil cohesion can well predict soil detachment capacity. Plant litter incorporation into soil is a widespread phenomenon in the natural environment. Accurate estimation of the soil detachment capacity (Dc) driven by overland flow under litter incorporation effects is crucial for improving soil erosion prediction. However, the effects of litter incorporation on soil detachment processes are often ignored, and the temporal variation of Dc under litter incorporation effects remains unclear for grassland in the Loess Plateau of China. In this study, two litter incorporation soil treatments (Bothriochloa ischaemum (L.) Keng. litter, and Artemisia sacrorum Ledeb. litter) and one bare soil treatment (control) were set. Flume tests with flow shear stress ranging from 5.66 to 22.11 Pa were conducted to simulate overland flow scouring and determine the temporal variation of Dc between May 2017 and October 2018 (nine times, a 524-day period). Furthermore, the key factors affecting Dc were identified. Our results showed that the temporal variation in Dc was consistent across the different soil treatments (two litter incorporation treatments and one bare soil control), showing a rapid decline and then fluctuating at a low level, with Dc ranging from 0.115 to 6.876 kg m−2 s−1. Incorporation of litter effectively reduced Dc , with the Dc of soil treatments incorporating litter being 15% to 29% lower than that of bare soil (2.110 kg m−2 s−1). Further analysis showed that the temporal variation in Dc was mainly affected by the development of a physical soil crust. Dc can be successfully estimated using a nonlinear equation incorporating flow shear stress and soil cohesion (R2 = 0.77, NSE = 0.65), which represent the erosive force and soil erosion resistance, respectively. Our study reveals the important role of plant litter in the soil detachment process and aids the understanding of soil erosion pathways. Further studies are needed to investigate the effects of a physical soil crust on the soil detachment process driven by overland flow. [ABSTRACT FROM AUTHOR]

Summary Sand burial and dew deposition are two fundamental phenomena profoundly influencing biological soil crusts in desert areas. However, little information is available regarding the effects of sand burial on dew deposition on biological soil crusts in desert ecosystems. In this study, we evaluated the effects of sand burial at depths of 0 (control), 0.5, 1, 2 and 4 mm on dew formation and evaporation of three dominant moss crusts in a revegetated area of the Tengger Desert (Northern China) in 2010. The results revealed that sand burial significantly decreased the amount of dew deposited on the three moss crust types by acting as a semi-insulator retarding the dew formation and evaporation rates. The changes in surface temperature cannot fully explain the variations of the formation and evaporation rates of dew by moss crusts buried by sand. The extension of dew retention time was reflected by the higher dew ratios (the ratio of dew amount at a certain time to the maximum value in a daily course) in the daytime, and may to some extent have acted as compensatory mechanisms that diminished the negative effects of the reduction of dew amount induced by sand burial of moss crusts. The resistances to reduction of dewfall caused by sand burial among the three moss crusts were also compared and it was found that Bryum argenteum crust showed the highest tolerance, followed by crusts dominated by Didymodon vinealis and Syntrichia caninervis . This sequence corresponds well with the successional order of the three moss crusts in the revegetated area, thereby suggesting that resistance to reduction of dewfall may act as one mechanism by which sand burial drives the succession of moss crusts in desert ecosystems. This side effect of dew reduction induced by sand burial on biological soil crusts should be considered in future ecosystem construction and management of desert area. [ABSTRACT FROM AUTHOR]

How soil cover types and rainfall patterns influence carbon (C) release in temperate desert ecosystems has largely been unexplored. We removed intact crusts down to 10 cm from the Shapotou region, China, and measured them in PVC mesocosms, immediately after rainfall. C release rates were measured in soils with four cover types (moss-crusted soil, algae-crusted soil, mixed (composed of moss, algae, and lichen)-crusted soil, and mobile dune sand). We investigated seven different rainfall magnitudes (0-1, 1-2, 2-5, 5-10, 10-15, 15-20, and >20 mm) under natural conditions. C release from all four BSCs increased with increasing rainfall amount. With a rainfall increase from 0 to 45 mm, carbon release amounts increased from 0.13 ± 0.09 to 15.2 ± 1.35 gC m in moss-crusted soil, 0.08 ± 0.06 to 6.43 ± 1.23 gC m in algae-crusted soil, 0.11 ± 0.08 to 8.01 ± 0.51 gC m in mixed-crusted soil, and 0.06 ± 0.04 to 8.47 ± 0.51 gC m in mobile dune sand, respectively. Immediately following heavy rainfall events (44.9 mm), moss-crusted soils showed significantly higher carbon release rates than algae- and mixed-crusted soils and mobile dune sands, which were 0.95 ± 0.02, 0.30 ± 0.03, 0.13 ± 0.04, and 0.51 ± 0.02 μmol CO m s, respectively. Changes in rainfall patterns, especially large rain pulses (>10 mm) affect the contributions of different soil cover types to carbon release amounts; moss-crusted soils sustain higher respiration rates than other biological crusts after short-term extreme rainfall events. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (BSCs) are extensively developed and commonly regarded as a kind of vegetation in desertification areas around the world. The natural recovery process of BSCs after disturbance and their long-term impacts on the soil water conditions are important but not well understood. In order to provide more insights into this problem, we set up two treatments including BSCs (natural BSCs without disturbance) and disturbed BSCs (the top 30mm of surface soil, including the BSC layer, was severely disturbed and completely removed) in a semi-arid environment on the Loess Plateau of China. Over the succeeding years, the natural recovery process of BSCs was qualitatively described and the soil water content at 0–90cm depth of the two treatments was consecutively monitored. The results showed the following: (1) it is possible to recover natural moss-dominated BSCs after severe disturbance under natural conditions, and the recovery process to BSC full-coverage took approximately three years; (2) the BSC disturbance greatly decreased soil water content by up to 18% and the effects gradually weakened with time; (3) the BSC disturbance decreased surface soil water content (0–70cm) by up to 24% but increased deep soil water content (80–90cm) by up to 13%; and (4) the BSC disturbance decreased soil water storage at 0–90cm by 7.8mm, 4.4mm, 8.0mm, and 4.9mm in the second, third, fourth, and seventh years, respectively. We concluded that the BSC disturbance degraded soil water conditions in the three to four years following the disturbance. Therefore, the artificial destruction of natural moss-dominated BSCs in a semi-arid region on the Loess Plateau of China should not be recommended as a land management practice for the improvement of soil water conditions. [Copyright &y& Elsevier]

Highlights: [•] Biological soil crusts significantly increased soil enzyme activities. [•] Moss crusts had greater soil enzyme activities than cyanobacteria–lichen crusts. [•] The elapsed time since sand dune stabilization correlated positively with soil enzyme activity. [•] Soil enzyme activities under crusts varied with soil depth and season. [Copyright &y& Elsevier]

Soil degradation by expansion-driven sealing increases at an unexpected rate globally, but the dynamics of agricultural soil sealing in peri-urban areas remain poorly understood. This study used aerial photographs to monitor patterns of built-up land expansion and subsequent agricultural soil sealing between 1994 and 2006 in peri-urban areas of Shanghai, China. Results indicated that a total of 152,706.5 ha of agricultural soils were sealed. In particular, residential land and industrial land were the major contributors. Buffer analysis demonstrated that agricultural soils with high proximity to roads and urban centers are more vulnerable to be sealed. Percentage of sealed agricultural soils of total agricultural soils had linear relationships with population growth and economic development. These results quantitatively document the impacts of urbanization on agricultural soil seating. From a management perspective, we argue that the protection of agricultural softs should be integrated with urban planning efforts in China. [ABSTRACT FROM AUTHOR]

Characteristics of water vapour condensation, including the onset, duration, and amount of water vapour condensation on moss-dominated biological soil crust (BSC) and dune sand were studied under simulated conditions with varying air temperature and relative humidity. The simulations were performed in a plant growth chamber using an electronic balance recording the weight of condensation. There was a positive linear correlation between the water vapour condensation and relative humidity while the mean temperature was negatively linearly related to amounts of water vapour condensation for both soil surfaces. The amount of water vapour condensation on BSC and dune sand can be described by the difference between air temperature and dew point with an exponential function, indicating that when the difference of air temperature and dew point exceeds a value of 35.3C, there will be zero water vapour condensed on BSC. In contrast, when the difference of air temperature and dew point exceeds a value of 20.4C, the water vapour condensation will be zero for dune sand. In general, when the air is fully saturated with water and the dew point is equal to the current air temperature, the water vapour condensed on BSC attained its maximum value of 0.398 mm, whereas it was 0.058 mm for dune sand. In comparison, water vapour condensed on BSC was at a relatively high temperature and low relative humidity, while we did not detect water vapour condensation on the dune sand under the similar conditions. Physical and chemical analyses of the samples pointed to a greater porosity, high content of fine particles, and high salinity for BSC compared to the dune sand. These results highlight that soil physicochemical properties are the likely factors influencing the mechanism of water vapour condensation under specific meteorological conditions, as onset was earlier and the duration was longer for water vapour condensation on BSC in comparison with that of dune sand. This contributed to the greater amount of vapour absorbed on BSC compared to the dune sand under an identical meteorological condition. The feedback of water vapour condensation on BSC formation and its contribution to sustain the revegetation desert ecosystems was discussed. [ABSTRACT FROM AUTHOR]

Plant interactions greatly affect plant community structure. Dryland ecosystems are characterized by low amounts of unpredictable precipitation as well as by often having biological soil crusts (BSCs) on the soil surface. In dryland plant communities, plants interact mostly as they compete for water resources, and the direction and intensity of plant interaction varies as a function of the temporal fluctuation in water availability. Since BSCs influence water redistribution to some extent, a greenhouse experiment was conducted to test the hypothesis that the intensity and direction of plant interactions in a dryland plant community can be modified by BSCs. In the experiment, 14 combinations of four plant species (Artemisia ordosica, Artemisia sphaerocephala, Chloris virgata and Setaria viridis) were subjected to three levels of coverage of BSCs and three levels of water supply. The results show that: 1) BSCs affected plant interaction intensity for the four plant species: a 100% coverage of BSCs significantly reduced the intensity of competition between neighboring plants, while it was highest with a 50% coverage of BSCs in combination with the target species of A. sphaerocephala and C. virgata; 2) effects of the coverage of BSCs on plant interactions were modified by water regime when the target species were C. virgata and S. viridis; 3) plant interactions were species-specific. In conclusion, the percent coverage of BSCs affected plant interactions, and the effects were species-specific and could be modified by water regimes. Further studies should focus on effects of the coverage of BSCs on plant-soil hydrological processes. [ABSTRACT FROM AUTHOR]

Large areas of farmland have been established in China's Loess Plateau region by backfilling forest and grasslands in gullies with topsoil from hillslopes. High amounts of plant litter are incorporated into the topsoil during such processes; however, their effects on soil erosion resistance under natural conditions are not fully understood. Therefore, the present study investigated seasonal variation in soil erosion resistance to overland flow and the underlying factors in the gully-filled farmland. Two typical plant litter species were selected in this study, i.e., Artemisia sacrorum Ledeb. (ASL) and Bothriochloa ischaemum (L.) Keng. (BIL). Overland water flow was tested under six shear stress levels (5.66–22.11 Pa) in natural soil samples incorporated with plant litter and without plant litter to determine soil erosion resistance parameters (rill erodibility K r and critical shear stress τ c). The study was conducted over 524 days (through May 6, 2017, to October 11, 2018), covering two rainy seasons and one winter. Soil properties changed significantly over time, with physical crust thickness and cohesion increasing from 0 to 10.7 mm and 2.9–13.4 kPa, respectively. In contrast, the mass density of incorporated plant litter decreased from 0.7 to 0.2 kg m−2. Soil erosion resistance increased with time, which showed that K r decreased (from 0.516 to 0.021 s m−1) and τ c increased (from 0.49 to 7.98 Pa). Compared with the initial state of new farmland (K r = 0.507 s m−1, τ c = 0.48 Pa), K r decreased by 77–96% and τ c increased 8–14 times at the end of the study. Plant litter incorporation markedly enhanced soil erosion resistance in a time- and species-dependent manner. Compared with the bare soil without plant litter, the K r values of ASL and BIL treatments were 3–64% and 2–83% lower, and their τ c values were 0–81% and 0–55% higher, respectively. K r was significantly and positively correlated with cumulative precipitation, cumulative rainfall kinetic energy, soil cohesion, and physical soil crust thickness, while τ c was negatively correlated with the influencing factors. Further, both K r and τ c could be well predicted by physical soil crust thickness and cohesion (R2 = 0.79 and 0.87, p < 0.01, n = 27). According to the results, seasonal patterns of soil erosion resistance in the gully-filled farmland established under plant litter incorporation were mainly controlled by rainfall and physical soil crust structure. This study provides a reference resource for soil erosion prediction in farmland ecosystems on the Loess Plateau. • We monitored K r , τ c and potential influencing factors over 524 days. • The soil with litter incorporation has better soil erosion resistance. • Litter in the soil promotes the formation of physical soil crust by increasing SCT and Coh. • K r and τ c can be well predicted by SCT and Coh. [ABSTRACT FROM AUTHOR]

Abstract: Dynamics of soil sealing and soil landscape patterns under rapid urbanization were qualified in the Urban Agglomeration around Hangzhou Bay (UAHB), China. Rapid population growth, economic development, and settlement sprawl were identified from 1994 to 2009. Such accelerating urbanization resulted in considerable soil sealing. For the entire region, percentage of sealed soils increased from 2.7% in 1994 to 4.7% in 2003 and to 8.7% in 2009. Paddy soils, especially those of the highest quality, were the first victims. Soil landscapes, at the regional scale, became more fragmented and irregular, but less dominated, diverse and connected as urbanization intensified. Spatial regression uncovered the diverging relationships between landscape metrics with urbanization indicators and measurement period. The dynamics of soil sealing and soil landscape patterns not only reflected common tendencies in China, but represented a global process. Our study provided a practical methodological framework, by integrating remote sensing, geographical information systems, landscape metrics and spatial regression, for monitoring the impacts of urbanization on soil resources. [Copyright &y& Elsevier]

Felsic intrusions in the Hannan region at the northwestern margin of the Yangtze Block mainly include the ca. 730 Ma adakitic Erliba and Wudumen plutons and the ca. 760 Ma calcic-alkali Xixiang and Tianpinghe bodies. These four intrusions were considered to have been formed by melting of the newly formed lower mafic crust. However, the two generations of granitoids have different lithologies and mineral compositions. Thermobarometry calculations reveal that the Erliba and Wudumen granitoids formed under approximately similar emplacement pressures (2.96–3.11 kbar) and temperatures (787–789°C). The Xixiang emplaced body was intruded at high pressure (˜3.54 kbar) and low temperature (˜676°C), whereas the Tianpinghe pluton solidified at low pressure (˜2.00 kbar) and high temperature (∼747°C). The four intrusions have similar oxygen fugacity ranges near the nickel-nickel oxide buffer, suggesting oxidized parental magmas. The Erliba and Wudumen are estimated to have been generated under pressures higher than 12 kbar, the Xixiang under a pressure of >10 kbar, and the Tianpinghe under a pressure of >6 kbar. Thus, the petrology and geochemical differences among these four felsic intrusions probably mainly resulted from variations of depth and degrees of partial melting. The whole-rock and mineral compositions have arc affinities, suggesting that they were formed in an active continental margin. [ABSTRACT FROM AUTHOR]

Abstract: Carbon flux represents carbon uptake from or release to the atmosphere in desert ecosystems, yet the changing pattern of carbon flux in desert ecosystems and its dependence on soil cover type and rainfall amount are poorly understood. We measured net carbon fluxes (NCF) in soil with four cover types (moss crusted soil, cyanobacteria/lichen crusted soil, bareland and semishrub Ephedra distachya-inhabited site) from April to October of 2010 and 2011, and NCF and dark respiration (DR) after four rainfall amounts (0, 2, 5, and 15 mm) in cyanobacteria/lichen crusted soil, bareland and the E. distachya-inhabited site. NCF in the E. distachya-inhabited site differed significantly from those of the other three soil cover types, while no difference was observed between the moss and cyanobacteria/lichen crusted soils or between the two crusted soils and bareland on most measurement occasions. NCF ranged from −0.28 ± 0.14 to 1.2 ± 0.07 μmol m−2 s−1 in the biologically crusted soils, and from −2.2 ± 0.27 to 0.46 ± 0.03 μmol m−2 s−1 at the E. distachya-inhabited site. Daily NCF in the biologically crusted soils and bareland showed carbon release at most times and total carbon production ranged from 48.8 ± 5.4 gC m−2 yr−1 to 50.9 ± 3.8 gC m−2 yr−1, while the E. distachya-inhabited site showed a total carbon uptake of −57.0 ± 9.9 gC m−2 yr−1. Daily variances in NCF were well-explained by variances in surface soil temperature, and seasonal NCF showed a significant linear relationship with soil moisture in the two biologically crusted soils and bareland when soil volumetric water content was less than 3%. Rainfall elicited intense carbon release in cyanobacteria/lichen crusted soil, bareland and at the E. distachya-inhabited site, and both NCF and DR were positive in the first two days after rainfall treatments. Mean NCF and DR were not different between rainfall amounts of 2, 5 and 15 mm in cyanobacteria/lichen crusted soil and bareland, while they were significantly higher after 15 mm rainfall treatment compared with 2 mm and 5 mm treatments at the E. distachya-inhabited site. Mean NCF and DR in the first two days increased logistically with rainfall amount. Based on our findings, we suggest that E. distachya-inhabited sites contribute to carbon uptake in the Gurbantunggute Desert, while biologically crusted soils exhibit carbon release for most of the year. Even though photosynthesis immediately following rainfall can be stimulated, carbon uptake effect in biologically crusted soil is likely intermittent and confined to periods when moisture is available. [Copyright &y& Elsevier]

Biological soil crusts (BSCs) perform essential ecosystem functions in arid and semi-arid ecosystems worldwide. The formation, development, and distribution of BSCs are influenced by changes in multiple environmental factors, including changes in the vascular plant community. The influence of changes in vegetation factors on BSC cover in 8-, 12-, and 16-year-old rehabilitated grasslands were studied in the hilly area of the Chinese Loess Plateau. The rate of degradation of BSCs underneath litter ( P < 0.01) and the degradation cover of BSCs ( P < 0.05) differed significantly between the 8- and 16-year-old successions. Stepwise multiple linear regression analysis showed that the main vegetation factors influencing the dynamics of BSC cover differed among the 8-, 12-, and 16-year-old rehabilitated grasslands. Basal cover, phytomass, and litter cover were the main vegetation factors influencing the dynamics of BSC cover on 8-year-old rehabilitated grassland. Phytomass, litter thickness, and litter cover were the main factors influencing the dynamics of BSC cover on 12-year-old rehabilitated grassland. On 16-year-old rehabilitated grassland, Pielou evenness index, litter thickness, and litter biomass were the main vegetation factors influencing degradation of BSC cover underneath litter, whereas basal cover, litter thickness, and litter biomass were the main vegetation factors influencing the degradation cover of BSCs. At particular stages of herbaceous succession, vegetation factors can have a large influence on changes in the community's basal cover and litter, which are key factors influencing changes in BSC cover. The degradation of BSCs underneath litter may be a result of complicated eco-physiological processes. [ABSTRACT FROM AUTHOR]

The importance of cyanobacterial polysaccharides of biological soil crusts in sand surface stabilization and soil nutrient retention has been long acknowledged. However, the role of cyanobacterial polysaccharides as a source of nutrition to vascular plants in crusted areas is ignored. In this study, the chemical composition of the polysaccharide synthesized by Phormidium tenue and the effects of its presence on seed germination and seedling metabolism of the shrub Caragana korshinskii were investigated. The crude polysaccharide synthesized by P. tenue was composed of 15 % protein and 58 % carbohydrate and showed the presence of 12 different types of monosaccharides. The addition of the polysaccharide significantly ( P < 0.05) increased seed germination and metabolic activity of the seedling of the shrub C. korshinskii. The optimal concentration for vigor index, root length, root vigor, and total N and P contents was 10 mg/L polysaccharide; for the germination rate, nitrate reductase activity, carbohydrate content, chlorophyll, and Mg content, the optimal was 60 mg/L polysaccharide, while for K and Ca contents, photosynthetic efficiency and superoxide dismutase activity was 120 mg/L. The presence of the polysaccharide increased seed germination rate, ion uptake, and photosynthetic activity by affecting the electron transport chain and decreased oxidative damage by eliminating reactive oxygen species in C. korshinskii, thus promoting shrub performance in crusted desert areas. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (BSCs) are important sources of carbon input to ecosystems in arid and semiarid regions, where vascular plants are restricted by the rigorous environment and limited soil water. Sand dune stabilization by revegetation can enhance colonization and development of BSCs on sandy soil surfaces, and convert BSCs from the early successional stage dominated by cyanobacteria and algae to the later stage dominated by lichens and mosses. This study estimated the carbon fixation by two successional stages of BSCs based on four years of field observations. Carbon fixation by two BSCs has been compared via estimating daily carbon fixation using measuring net photosynthesis with ten sampling plots per crust stage in situ, combining with calculating the wet daytime of crustal cryptogam thallus. However, diurnal carbon fixation of both BSCs was largely determined by crustal water content rather than photosynthesis photon flux and temperature. The range of optimal gravimetric water content for early BSCs was 1–3.5%, and 1–5% for the later BSCs. The annual carbon fixation was 11.36gCm−2 yr−1 for cyanobacteria–algae dominated crusts and 26.75gCm−2 yr−1 for lichen–moss dominated crusts. The latter had a higher carbon input due to a higher water-holding capacity, prolonging wet daytime and higher chlorophyll content, as well as higher light capture. These findings indicate the recovery of BSCs is expected to significantly increase carbon input into sandy desert ecosystems. [Copyright &y& Elsevier]

Abstract: Different from soils in other ecosystems, soils in arid and semiarid areas are covered by biological soil crusts, which can both assimilate and release carbon via their physiological activities. Nevertheless, few studies have evaluated carbon flux in biologically crusted soils. In the current study, we investigated the daily carbon flux in moss- and cyanobacterial/lichen-crusted soils, as well as crust-removed soil (referred as bareland) in the Gurbantunggut Desert, Northwestern China from April to October 2010. We also investigated carbon flux in biologically crusted soils after 0, 2, 5, and 15mm precipitation treatments. Carbon flux between crusted soil and bareland had no significant difference, with average values of 0.16, 0.2, and 0.12μmolm−2 s−1 for moss-crusted soil, cyanobacterial/lichen crusted soil, and bareland, respectively. The corresponding Q 10 values for the three soils were 2.9, 3.5, and 1.9, respectively. Precipitation significantly elicited carbon flux, reaching a maximum value of 2.4μmolm−2 s−1. After precipitation, the net carbon flux in light was lower than that in dark respiration. No carbon influx was observed in light condition. The average carbon flux rate and total carbon production increased exponentially with the precipitation amount. This study indicates that biological soil crusts do not increase the respiration of soil, but increases the temperature dependence of soil carbon flux because of the higher microbial biomass than bareland. [Copyright &y& Elsevier]

Purpose: Sealing of soils prevents the exchange of gas, water and nutrient between soil and other environmental compartments, and affects urban N flux, thereby resulting in certain negative impacts on soil functioning and urban environment. However, little information is available on the biogeochemical cycling and biological activities after sealing of soils in urban areas. The aim of this study was to assess the effects of soil sealing on N transformation and associated microbial properties. Materials and methods: Soil samples were collected at four depths (0-10, 10-20, 20-30, 30-40 cm) from three land cover types: impervious land (sealing of soil), forest (vegetation) and bare land (no sealing and no vegetation) in Beijing, China. Soil inorganic N, net potential N-mineralization and nitrification rates, physicochemical properties, microbial biomass and activities of urease, protease and nitrate reductase were analyzed. Results and discussion: Sealing of soils affected soil physicochemical properties, nutrient availability and microbial characterizations, which resulted in the reduction of soil net potential mineralization and nitrification. Soil pH and C/N ratio were increased while soil organic matter and total N were decreased after sealing of soils, especially in the 0-10 cm layer. Impervious sites had the lowest soil microbial biomass C (10.52-26.26 mg kg) and N (10.52-26.26 mg kg) among the three types of soils. In addition, microbial biomass increased along the depth gradient. Soil enzyme activities were also significantly affected by sealing of soils. Canonical correlation analysis suggested that reduction of soil net potential mineralization and nitrification in impervious sites was mainly caused by the variation of soil total N, soil organic matter and soil microbial biomass. Conclusions: Sealing of soils remarkably influenced the soil N transformation process and soil microbial activities in urban areas. Thus, our results suggested that reducing the negative effects of soil sealing on paved and unpaved areas could be useful measures to improve urban soil functions, and hence facilitate the remediation of the adverse impacts caused by urban N deposition. [ABSTRACT FROM AUTHOR]

Biological soil crusts occur in dry land worldwide. However, studies on the carbon exchange of crusts with different histories of crust development are rare, especially in terms of the responses of carbon exchange to increasing atmospheric CO2 concentrations and decreasing water contents of crust organisms. In this study, we classified sites in Shapotou in the Tengger Desert as recent (site revegetated in 1981 in mobile sand dunes) and old (site revegetated in 1956) successional stages, and systematically analyzed the changes in the carbon exchange of cyanobacterial-algal crusts developed in the two sites to dehydration, air temperature (15 and 25 °C), and CO2 concentration (200–2000 ppm). The old crusts had a higher carbon exchange rate than the recent crusts during dehydration, and the maximum carbon exchange rates were 3.49 and 2.45 µmol · m−2 · s−1 for the old and recent crusts, respectively, at an approximately 60% water content of dry crust organisms. The carbon exchange rate was higher at 25°C than at 15°C for both crusts. No difference in the CO2 saturation points between the two crusts and between the two temperatures was observed, however, the saturation point significantly increased with the increase in the water content of the crust organisms, from 224 to 1384 ppm, when the water content of the crust organisms was increased from 20% to 100%. The water content of the crust organisms was the regulating factor for the carbon exchange rate of both the old and recent cyanobacterial-algal crusts. [ABSTRACT FROM AUTHOR]

Quantification of the relationship between surface albedo and surface temperature was done by analyzing measured diurnal variations of surface albedo and surface temperature on the biological soil crusts and sand dunes within vegetation-stabilized desert ecosystems. The surface albedos and surface temperatures of sand dunes and biological soil crusts were measured concurrently over field plots of the moving sand area and the artificially revegetated area established in 1964 in Shapotou area, on the southeastern edge of the Tengger Desert. Results indicated that the diurnal variation of surface albedo for both dry surfaces showed an upward-facing parabolic curve on clear days and was symmetrical at about local noon. Whereas, the diurnal trend of surface temperature was opposite to that of surface albedo in the daytime and asymmetrical at about local noon times. Thereby, the data were empirically divided into forenoon and afternoon data with respect to local noon to analyze the relationship between surface albedo and surface temperature. A highly correlated negative linear relationship was found in the two time periods, respectively, and we proposed an empirical model between surface albedo and surface temperature based on that relationship. The model results indicate a good potential application for using the surface temperature to specify surface albedo. [ABSTRACT FROM AUTHOR]

In order to investigate succession of biological soil crusts (BSCs) and their microstructure variability, we conducted this work in Shapotou revegetation region at the southeast edge of Tengger Deser. The results showed that BSCs generally succeeded as a pathway of 'Algae crusts, algae-lichen crusts, lichen crusts, lichen-moss crusts and moss crusts'. Occasionally mosses directly occurred on algae crusts, and BSCs succeeded from algae crusts to moss crusts. Crust vertical stratification was a common phenomenon, from top to bottom an inorganic layer, algae-dense layer and algae-sparse layer were divided in algae crusts; a thallus layer, rhizoid layer and sub-rhizoid layer in lichen crusts; a 'stem-leaf' layer, rhizoid layer and sub-rhizoid layer in moss crusts, respectively. The main crust binding organisms varied from filamental cyanobacteria (dominated by Microcoleus) in algae crusts to lichen rhizoids, free-living cyanobacterial filaments and fungal hyphaes in lichen crusts, and to moss rhizoids and fungal hyphaes in moss crusts. The dominant phototrophic organisms varied from Microcoleus (algae) in algae crusts to Collema (lichens) in lichen crusts, and to Bryum (or Didymodon and Tortula; mosses) in moss crusts. Total phototrophic biomass increased while the free-living algal biomass decreased with the succession of BSCs. In addition, exopolysaccharides and fine particles accumulated in the course of development and succession of BSCs, all of which lead to a gradual increase in crust thickness and porosity, while decrease in the bulk density. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (BSCs) play an important role in the dune fixation and maintaining soil biota in arid desert systems. Free-living soil nematode communities could be used as significant bioindicators to reflect soil recover regime after sand burial. However, the relationship between BSCs and nematodes is rarely known. To examine the effects of BSCs on soil nematodes, 72 soil samples under cyanobacteria–lichen and moss crusts were collected to analyse nematode communities in the different aged vegetated areas at the southeastern edge of the Tengger Desert. Our results showed the colonization and development of BSCs significantly enhanced nematode diversity. Nematode abundances, generic richness, H′, MI, EI and SI were greater under crusts than those under noncrust. In particular, nematode abundances, generic richness, H′, MI, EI and SI were positively correlated with crust ages. The differences in nematode communities were also dependent upon crust types. Nematode abundances and generic richness under moss crusts were higher than those under cyanobacteria–lichen crusts. This can be contributed to the present and succession of BSCs that increased thickness of topsoil after dunes have been stabilized, namely, creating suitable habitats and providing an essential food source for nematodes. [Copyright &y& Elsevier]

Abstract: The eastern part of the North China Craton in eastern Hebei Province contains metamorphosed and deformed Neoarchaean to earliest Palaeoproterozoic rocks (∼2550–2490Ma) with some older Archaean rocks. Numerous precise U–Pb zircon ages, structural observations, Nd and Hf isotopic data and whole rock geochemistry (our new data with reassessment and integration of previous work) show that there is not a single protracted event at the end of the Archaean lasting ∼60 million years, but that from east to west there are several separate events with their own unique character. The eastern coastal region is dominated by weakly deformed 2530–2510Ma granites with subordinate granodiorites, diorites and magnesian-gabbros. This suite has inclusions of older 2550–2540Ma plutonic rocks. ∼80km inland to the west, there are amphibolite facies biotite-rich schists, lenses of BIF, siliceous fuchsite bearing rocks with 3880–3540Ma zircons, peridotites and orthogneisses, all intruded by younger granites and monzonites. Three amphibolite–granulite facies gneisses and schists with volcano-sedimentary protoliths have 2548–2534Ma igneous zircon populations, rare inheritance back to >3600Ma and 2506±6Ma zircon equated with granulite facies metamorphism. Older tonalitic to granitic polyphase orthogneisses contain 3287±11Ma to ∼2940Ma igneous components. Late kinematic high Fe/Mg gabbros, monzonites and granites have ages of 2499±7 to 2491±13Ma. 160–100km inland, gneissose 2550–2530Ma quartz-diorite to tonalitic rocks occur as intrusions into, or intercalations with, mafic rocks. These were affected by granulite facies metamorphism but then widely retrogressed. Abundant syn-granulite facies neosome and later shear zones disrupt the early geological relationships. The granulite facies metamorphism is dated at 2503±5Ma from several samples, including a syn-granulite facies pegmatite. The Neoarchaean igneous rocks show marked negative Nb, Ti anomalies, LIL enrichment and enrichment of the light REE relative to the heavy REE across the entire ultramafic, basaltic, tonalitic and granitic compositional spectrum: 2550–2530Ma tonalites and quartz diorites are most important in the west and 2530–2510Ma granites are most important in the east. Their composition resembles those formed at various stages of magmatic arc evolution at a convergent plate boundary, rather than being plume products. The eastern Hebei rocks thus formed in a complex arc with distinct pulses of plutonism at 2550–2540 and 2530–2510Ma, with local incorporation of older continental crust. The 2500–2490Ma thermal event with its associated higher Fe/Mg magmas involved interaction of underplated fractionated gabbroic melt with deep crustal melts, possibly during extension of an already ∼50 million years old arc. [Copyright &y& Elsevier]

In Gurbantunggut Desert, cyanobacterial and microalgal components were characterized within 60 soil samples collected from sand dunes. Fifty-one taxa of cyanobacteria and algae were identified. Without exception, the soils were alkaline, poor in nutrients, and showed large variations in other soil properties. Spatial heterogeneity for distribution of cyanobacteria and microalgae (diversity of morphotypes, species composition, and microbiomass) existed. Compared with other deserts in the world, the Gurbantunggut Desert has a greater diversity of cyanobacterial-microalgal morphotypes. Results from step regression showed that the diversity of morphotype was determined by total P, available P, and soil layer. Filamentous cyanobacteria dominated the community. Microcoleus vaginatus (Vauch.) Gom was the dominant species in most positions on sand dune, while the abundance of other dominant species varied depending on the sand dune position and the soil layer in which they occurred. The microalgal biomass was influenced by the content of Mg, crust type, soil moisture, sunlight, and oxygen concentration. A significant positive relation was found between microalgal biomass and diversity of morphotype. Species composition, diversity of morphotype, and microalgal biomass interacted with each other. The contents of P and Mg ion, soil texture, and soil moisture may be the main factors responsible for cyanobacterial-microalgal distribution. [ABSTRACT FROM AUTHOR]

Abstract: The North Qinling terrain reveals a different geological history from the North China block to the north and the South Qinling micro-continental block to the south. The timing of events and geochemical features of the North Qinling terrain are essential for understanding the evolution of the Qinling orogenic belt that joins the North and South China blocks. This study presents detrital zircon ages and Hf isotopic compositions from the Guandaokou Group, a cover sequence of the North China block, and from the Kuanping Group, an upper basement sequence of the North Qinling terrain. The youngest detrital zircon U–Pb ages constrain the initiation of sedimentation in the Guandaokou Group to 1.85Ga and the maximum depositional age of the Kuanping Group to ~640Ma. Zircon U–Pb ages and Hf data testify to a major phase of magmatism in the North Qinling terrain at ~1000–900Ma. The magmatic rocks were largely produced from reworking of early Paleoproterozoic (~2.5–2.0Ga) crust with minor contribution of late Paleoproterozoic (~1.7Ga) juvenile material. This age record differs in time from the two important thermal events of ~1.85Ga and ~2.5Ga, widely manifested in the North China block. The North Qinling terrain can thus be regarded as a separate micro-continent with a pre-Neoproterozoic evolution different from that of the North China block. The final assembly of the North Qinling terrain to the North China block took place after about 640Ma. [Copyright &y& Elsevier]

Abstract: Biological soil crusts (BSCs) are the primary source of soil nitrogen in dry areas. We investigated the nitrogenase activity of three BSC types from the Tengger desert in responses to stimulated precipitation, temperature, and irradiance intensity. In addition, potential seasonal nitrogen fixation by BSCs was estimated using meteorological records. The nitrogenase activity of BSCs ranged from 2.6 to 16.6 mmol m−2 h−1 in this desert, and nitrogenase activity was significantly dependent on crust type, precipitation, and temperature, but not on irradiance. Cyanobacterial–algal crusts showed the highest nitrogenase activity (16.6 mmol m−2 h−1), followed by lichen crusts (6.9 mmol m−2 h−1), and moss crusts (2.6 mmol m−2 h−1). Cyanobacterial–algal crusts demonstrated maximum nitrogenase activity with 1.54 mm of precipitation, while the maximum activity for lichen and moss crusts occurred at 1.83 mm and 0.65 mm, respectively. The optimum temperature for nitrogenase activity ranged from 15 to 30 °C. Based on meteorological data, the potential nitrogen input was estimated to be 3.7–13.2 g m−2 a−1, and the high nitrogen fixation in this region resulted from the perfect match of optimum climate to the favorable environmental factors for BSC nitrogenase activity. This study demonstrated that BSCs are the main nitrogen input source in this temperate desert ecosystem. In particular, cyanobacterial–algal crusts, which are the first colonizers of the desert ecosystem, may mediate the majority of nitrogen fixation to facilitate soil nitrogen accumulation in these infertile soils. [Copyright &y& Elsevier]

Abstract: Biological soil crusts are receiving increasing attention due to their potentially positive effects on desert ecosystems. Artificial propagation of crusts is one way to restore degraded desert soils. However, little is known about their effectiveness on overland flow or water infiltration. Consequently, a study was done on soils of the Loess Plateau of China that had crusts propagated on different slopes. The results show that: (1) it is feasible to artificially grow moss-dominated biological soil crusts (moss crusts) in laboratory; when inoculated by sprinkling crushed fragments of stems and leaves of natural moss crusts they will cover the soil surface almost completely after about 10 months; (2) the artificially propagated moss crusts significantly increase infiltration consequently decreasing overland flow and this increase in infiltration is positively correlated to the soil coverage extent; (3) overland flow results increased by slope in moss-protected and bare soils, consequently the action of moss crusts is particularly important for protecting steep slopes; (4) the start time of runoff process is delayed by moss crusts, and the soil water redistribution process is also greatly affected. These results may be useful for helping to control desertification on the Loess Plateau of China or similar regions. [Copyright &y& Elsevier]

The article presents a study of the structure of weathering crusts in the Russian Upper Amur region. Weathering crust composition was analyzed in three types of objects from the Dzhalta ore cluster of Stanovoi, Russia, namely sulfide copper-nickel ores, rocks in fault zones, and pyroxenite dikes barren of visible sulfide mineralization. Hand specimen sampling of the drill core suggests that copper and nickel contents are as high as six and 1%, respectively. Weathering crust composition includes green unconsolidated material with montmorillonite and an admixture of comparatively decomposed feldspar and pyroxene crystals and goethite. The study suggests that the composition of weathering crusts is variable across the region depending on the source rock composition.

Abstract: Since the pioneer wide-angle seismic profile along the Yadong–Gulu rift acquired in 1974 by the ex-Institute of Geophysics, Chinese Academy of Sciences (CAS), several research programs aimed to deep geophysics, performed thanks to the participation of Chinese national and international institutions, have been developed during last 35years, including 23 wide-angle seismic profiles with total length of about 6000km. These profiles are unevenly distributed, most of them in eastern Tibet and few profiles in western Tibet. In this paper, we make a summarized presentation of all these wide-angle seismic profiles and provide an overall view of the seismic velocity structure of the crust beneath the broad Tibetan plateau, which is the product of the continuous convergence and collision of the Indian and Eurasian plates since about 50Ma ago. Different patterns of crustal thickness variation related to the tectonic blocks and along suture zones of the region are displayed. The crust thickness is confirmed to be about 70–75km under southern Tibet, and 60–65km under northern, northeastern and southeastern Tibet. The leading edge of the subducted lithosphere reaches the northern margin of the plateau and directly contacts with Tarim Basin. Westward of the 90°E boundary, the Indian crust is moving towards the northern edge of the plateau and collides with Tarim Basin at 80°E while reach the Bangong–Nujiang suture belt at 88°E; eastward of the 90°E boundary, the northern edge of the crust should be at 50–100km south of Bangong–Nujiang suture. The results supply helpful constrains to understand the mechanism of the continent–continent collision and its consequences in the plateau and neighbouring areas. [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]