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Background: Annual herbs are crucial components of sandy ecosystems and their community assembly in arid sandy dunes is an intuitive indicator of a degraded ecosystem's successful restoration. In sandy areas, biocrust and sand burial often co-occur, given the higher diversity and biomass of annual herbs where both factors co-occur than where either does alone. Yet our knowledge of the underlying mechanism is limited. Methods: A field survey was conducted to verify that the presence of biocrust and sand burial jointly promoted the assembly of herbs. And then controlled simulating experiments were conducted to investigate the individual and collective effects of three biocrusts (bare sand (control), cyanobacterial crust, and moss crust) and three depths (0 (control), 2.5, and 5 mm) of sand burial upon germination, growth of three annual herbs as well as the soil water and nutrition status in a revegetated area of the Tengger Desert. Results: Biocrust inhibited seed germination of the three annual herbs, but promoted their seedling growth. However, sand burial disrupted the inhibitory influence upon seed germination and strengthened the positive effects of biocrust on seedling growth of all species, by improving the availability of water and nutrients in upper soil. Conclusion: Mutual complementary effects of biocrust and sand burial promote the establishment, and overall recruitment success of annual herbs. This finding emphasizes the importance of buried disturbance of biocrust in plant community assembly processes, providing an approach to disentangle relationships between biocrust and vascular plants, and a new technique suggestion for ecological restoration in arid sandy areas. [ABSTRACT FROM AUTHOR]

UV-B radiation is an important environmental factor affecting the composition and function of biological soil crusts (BSCs). The aim of this study was to compare the effects of enhanced UV-B radiation on BSCs from Tengger Desert, north-western China, which are dominated by the cyanobacterium Microcoleus vaginatus Gom. and moss Bryum argenteum Hedw. The BSCs were exposed to four UV-B supplemental treatments, including 2.75 (control), 3.08, 3.25, and 3.41 W m–2, for 40 days under field condition. In both the studied organisms, UV-B radiation significantly affected the physiological properties (total flavonoids, soluble proteins, soluble sugars, and proline contents). While marginally enhanced UV-B radiation for a short period favoured the growth of M. vaginatus and B. argenteum , excessively high and prolonged UV-B radiation suppressed the physiological properties of the two organisms. Moreover, response index revealed that UV-B radiation had more detrimental effects on B. argenteum , suggesting that B. argenteum is more sensitive to UV-B radiation than M. vaginatus. The findings of this study could help to predict and evaluate the possible changes in the structure and function of desert ecosystems, based on the variation in physiological responses of M. vaginatus and B. argenteum to enhanced UV-B radiation. Effect of enhanced UV-B radiation on terrestrial organisms and ecosystems has caused concern. Here, physiological responses of two dominant species in BSCs to enhanced UV-B radiation were compared, and the results indicated that enhanced and prolonged UV-B lead to deleterious effects to both species. The findings imply the structure and function of BSCs may influence by increased UV-B radiation. [ABSTRACT FROM AUTHOR]

Aims: Global climate change may greatly alter the structure and stability of drylands, creating an urgent need to recover their functions and services. Biological soil crust (biocrust), an interface between the soil and atmosphere, plays a crucial role in ecohydrological processes, and thus in influencing the restoration dynamics of dryland ecosystems. Previous studies have generally investigated the influences of biocrust on ecohydrological processes as an exogenous factor. However, it remains unclear how biocrusts, as an integral part of many ecosystems (i.e., as a system state variable), will change under global climate change.Methods: This study developed a new ecohydrological model with biocrust cover as a system state variable, and explored the response of dryland ecosystems to altered rainfall regimes.Results: Biocrust cover responded with an inverted U-shaped curve relationship to increasing annual rainfall and linearly to increasing rainfall frequency. Vascular plant (grass and shrub) cover showed an increasing trend with increasing annual rainfall and a decreasing trend to increasing rainfall frequency. Therefore, biocrust usually dominated over vascular plants (i.e., high biocrust cover and low vascular plant cover) under low annual rainfall. Furthermore, an increasing rainfall frequency would amplify the range of environmental (rainfall) conditions dominated by biocrust from an annual rainfall 0-100 mm under a rainfall frequency of 0.025 day−1 to 0-500 mm under a rainfall frequency of 1 day−1.Conclusions: This study developed a model framework to predict dryland dynamics for surfaces covered by biocrust under global climate change. We suggest that restoration efforts could target at biocrust-dominated state in deserts, especially in a (future) drier climate. [ABSTRACT FROM AUTHOR]

Biocrusts are a crucial component of desert ecosystems, playing a significant role in greenhouse gas fluxes when they cover soils. However, little is known about whether, and how sand burial, one of the most common disturbances affecting the biodiversity and ecological function of biocrusts, influences fluxes of CO 2 , CH 4 , and N 2 O from the desert biocrust-covered soils. Based on measurements of the fluxes of three greenhouses gases from soils covered with two kinds of biocrusts separately dominated by mixed (i.e., approximately 50% algal coverage and 50% lichen coverage of Endocarpon pusillum Hedw., here cyanobacteria are classed as algae) and moss (i.e., 100% coverage of Didymodon vinealis (Brid.) Zand.) crusts respectively, followed by zero (control), 1 mm (shallow burial), and 10 mm (deep burial) burial depths of sand, we studied the effects of short (20 days) and relatively long periods (one year) of sand burial on the fluxes of three greenhouse gases as well as their relationships with soil temperature and moisture at Shapotou on the southeastern edge of the Tengger Desert. The results of this study showed that sand burial had a significantly positive effect on emission fluxes of CO 2 and a negative effect on uptake of CH 4 by soils covered with the two types of biocrusts ( P < 0.05), but had a differential effect on N 2 O fluxes depending on burial depth. Shallow burial dramatically increased N 2 O emissions from the biocrust-covered soils ( P < 0.05), but the opposite was observed under deep burial. As burial time increased, the increase of CO 2 emissions decreased, but changes in fluxes of CH 4 and N 2 O varied with biocrust types and burial depths, respectively. In addition, results showed that CO 2 fluxes from the two biocrusts were closely related to soil temperature and moisture; thereby increased with the raised soil temperature at 5 cm depth and soil moisture caused by sand burial. In contrast, CH 4 and N 2 O emissions were not clearly related to temperature or moisture. Overall, the increase in global warming potential caused by sand burial indicates that this kind of deposition may aggravate the greenhouse effect of desert areas covered with biocrusts. [ABSTRACT FROM AUTHOR]

Biological soil crusts (biocrusts) are considered “desert ecosystem engineers” because they play a vital role in the restoration and stability maintenance of deserts, including those cold sandy land ecosystems at high latitudes, which are especially understudied. Microorganisms participate in the formation and succession of biocrusts, contributing to soil properties’ improvement and the stability of soil aggregates, and thus vegetation development. Accordingly, understanding the composition and successional characteristics of microorganisms is a prerequisite for analyzing the ecological functions of biocrusts and related applications. Here, the Hulun Buir Sandy Land region in northeastern China—lying at the highest latitude of any sandy land in the country—was selected for study. Through a field investigation and next-generation sequencing (Illumina MiSeq PE300 Platform), our goal was to assess the shifts in diversity and community composition of soil bacteria and fungi across different stages during the succession of biocrusts in this region, and to uncover the main factors involved in shaping their soil microbial community. The results revealed that the nutrient enrichment capacity of biocrusts for available nitrogen, total nitrogen, total phosphorus, total content of water-soluble salt, available potassium, soil organic matter, and available phosphorus was progressively enhanced by the succession of cyanobacterial crusts to lichen crusts and then to moss crusts. In tandem, soil bacterial diversity increased as biocrust succession proceeded but fungal diversity decreased. A total of 32 bacterial phyla and 11 fungal phyla were identified, these also known to occur in other desert ecosystems. Among those taxa, the relative abundance of Proteobacteria and Cyanobacteria significantly increased and decreased, respectively, along the cyanobacterial crust–lichen–moss crust successional gradient. However, for Actinobacteria, Chloroflexi, and Acidobacteria their changed relative abundance was significantly hump-shaped, increasing in the shift from cyanobacterial crust to lichen crust, and then decreasing as lichen crust shifted to moss crust. In this process, the improved soil properties effectively enhanced soil bacterial and fungal community composition. Altogether, these findings broaden our understanding about how soil microbial properties can change during the succession of biocrusts in high-latitude, cold sandy land ecosystems. [ABSTRACT FROM AUTHOR]

• NA of biocrusts is mainly determined by surface soil water. • NA of cyanobacteria- was higher than that of moss-dominated crust when not restricted by water. • NA of moss- was related with micro-biomass C, but oxidable C for cyanobacteria-dominated crust. In arid desert regions, a large proportion of the ground surface is covered by specialized organisms such as cyanobacteria and mosses that form biological soil crusts (BSCs), which have multifunctionality in the ecosystem via stabilizing soil and fixing nitrogen (N) and carbon (C). Climate change, especially variations in rainfall will alter BSC species composition, cover and biomass, shaping the N-fixation of BSCs. Although BSCs are main contributors of N in desert ecosystems, it is not clear how nitrogenase activity (NA) of BSCs responds to changes in rainfall amount and frequency to function in the N-cycle. To address this important knowledge gap, based on long-term rainfall monitoring and predicted scenarios, we designed five levels of rainfall amount ranging from decreased by 50% to increased by 50%, and five rainfall frequencies ranging from increased by 100% to decreased by 80%, to simulate the potential variation of rainfall using rainout shelters. The NA of bare soil and cyanobacteria- and moss-dominated crust soil (three soil types) was determined by acetylene reduction assay. The soil water content (SWC), oxidable C and microbial biomass C and N were also determined. The NA of the three soil types was positively correlated with their SWC when rainfall amount decreased. In the case of increased rainfall frequency, NA of bare soil and moss-dominated crust was positively correlated with SWC, but negatively correlated for cyanobacteria-dominated crust. However, with increased rainfall amount combined with decreased rainfall frequency, there was no significant relationship between NA and SWC. In addition, NA of BSC was higher than that of bare soil with increased rainfall amount combined with decreased rainfall frequency, while that of bare soil was higher than that of BSC for decreased rainfall amount combined with increased rainfall frequency. In the case of increased frequency combined with decreased rainfall amount, the NA was higher for moss-dominated than cyanobacteria-dominated crust, but higher for cyanobacteria-dominated than moss-dominated crust for reduced rainfall frequency combined with increased rainfall amount. Meanwhile, NA of both bare soil and moss-dominated crust was correlated with microbial biomass C; and NA of cyanobacteria-dominated crust was positively correlated with SWC as well as oxidable C. Our findings indicated that future changes in rainfall regime will strongly affect NA of BSCs and bare soil in arid desert regions, and consequently change the soil fertility and net primary production. [ABSTRACT FROM AUTHOR]

• A stochastic shock model is proposed to investigate seed banks persistence. • The lower bound of the probability of seed bank persistence under stochastic shocks is presented. • The seed bank persistence of artificial sand-binding vegetation was investigated. Seed bank persistence plays a significant role in maintaining the sustainability of artificial vegetation in desert regions. However, the periods of droughts after each rainfall event form a series of stochastic shocks and result in depletion of the seed bank. Understanding seed bank persistence under stochastic shocks is a crucial prerequisite to evaluation of the sustainability of artificial vegetation under ongoing drought, but few studies have addressed the response of soil seed bank persistence to frequent stochastic shocks in deserts. In this paper, a stochastic shock model describing the input–output process of the seed bank is proposed based on modern risk theory to explore seed bank persistence of artificial vegetation in desert regions. The existence condition of the seed bank and the lower bound of the probability of seed bank persistence under stochastic shock after a long time were theoretically determined. As a verification of the theoretical model, seed bank persistence of artificial sand-binding vegetation on the southeastern margin of the Tengger Desert in China was investigated based on field observation and experimental and empirical data. The numerical results reveal that the seed bank of artificial sand-binding vegetation will always exist under stochastic shocks with a probability greater than 95%, suggesting that in the long-term succession process the current artificial sand-binding vegetation will likely maintain the development trend toward the adjacent natural vegetation. [ABSTRACT FROM AUTHOR]

• A novel integrated method based on VMD, the GWO algorithm and the SVM was proposed to estimate the monthly evapotranspiration in the southeastern margins of the Tengger Desert, China. • The proposed estimation model simultaneously conducts parameter optimization and the selection of data preprocessing techniques. • The proposed models only require historical monthly evapotranspiration data for observation. • The hybrid VMD-GWO-SVM model exhibited better computing performance than other hybrid models. Evapotranspiration (ET) plays a vital role in the water cycle and energy cycle and serves as an important linkage between ecological and hydrological processes. Accurate estimation of ET based on data-driven methods is of great theoretical and practical significance for exploring soil evaporation, plant transpiration and the regional hydrological balance. Most existing estimation approaches were proposed based on multiple meteorological variables. This study proposed a novel hybrid estimation approach to estimate the monthly ET using only historical ET time series in the southeastern margins of the Tengger Desert, China. The approach consisted of three sections including data preprocessing, parameter optimization and estimation. The model evaluation demonstrated that the hybrid model based on the variational mode decomposition (VMD) method, grey wolf optimizer (GWO) algorithm and support vector machine (SVM) model achieved superior computational performance compared to the performance of other methods. The Nash–Sutcliffe coefficient of efficiency (NSCE) increased from 0.8588 to 0.8754 and the mean absolute percentage error (MAPE) decreased from 28.42% to 23.22% in the testing stage. Thus, we suggest that the hybrid VMD-GWO-SVM model will be the best choice for estimating ET in the absence of regional meteorological monitoring. [ABSTRACT FROM AUTHOR]

Aims: Desert regions are regarded as highly sensitive to climatic changes. In arid and semi-arid desert, photosynthetic organisms from biological soil crusts are poikilohydric and sensitive to fluctuations in precipitation. How do physiological properties such as concentration of biochemical constituents and enzymes respond to a precipitation gradient from semi-arid to arid desert regions? Methods: We sampled cyanobacteria and moss crusts from four desert regions with distinctly different amounts of annual rainfall. Subsequently, the contents of photosynthetic pigments, malondialdehyde (MDA), osmotic adjustment substances, and antioxidative enzyme activities were correlated with the means of annual precipitation, evaporation, and temperature at the various sites. Results: Crust type, precipitation level, and their interaction had significant influences on many physiological properties (photosynthetic pigments, proline, soluble sugar, and superoxide dismutase). The contents of soluble protein, proline, and soluble sugar of cyanobacteria/moss crusts decreased with increasing precipitation level. Superoxide dismutase and catalase activities of cyanobacteria crusts decreased significantly with increasing annual precipitation. No significant variations in MDA were observed between different precipitation regions in the two crusts. Conclusions: Among the environmental variables tested, the annual amount of precipitation had the strongest effect on the physiological properties of moss/cyanobacteria crusts in different regions. Crust type combined with particular precipitation level influenced the physiological properties of crusts. Moreover, both moss and cyanobacteria crusts exhibited strong physiological adaptability to changes in precipitation. This result needs to be incorporated into future ecological models, which will help in understanding the function and vulnerability of biocrusts in the face of climate change. [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]

Biocrusts are critical biological components of drylands and play an important role in soil carbon (C) cycling. However, the effect of biocrusts on soil CO 2 exchange across global gradients of temperature and moisture is poorly understood. Moreover, their response to climate change remains highly uncertain. Bayesian hierarchical meta-analyses were performed on 47 published studies to quantify the impact of biocrusts on net soil exchange (NSE) of carbon- the difference between respiration and photosynthesis. Meta-analyses were also used on 23 studies to examine the effects of experimental warming on NSE in biocrusts. Meta-regressions further explored the thermal and wetness sensitivities of biocrust NSE and potential adaptation of biocrust responses to climate change. The development of biocrusts in dryland soils significantly increased NSE by 66.5 [22.2, 112.2] g C m−2yr−1, despite seasonal fluctuations, indicating a net loss of carbon to the atmosphere. Experimental warming, on average, increased biocrust NSE by 22.9 [-0.1, 40.8] g C m−2yr−1 per °C. However, across the spatial climate gradient, aridity limited the effects of warming, while high temperature decreased the thermal sensitivity of biocrust NSE, thus supporting the thermal adaptation of biocrusts. These results emphasize the critical role of biocrusts in modulating soil carbon exchange in response to climate warming across drylands, with particularly high thermal sensitivity in cool and moist regions. This highlights the need to incorporate biocrusts into global carbon budgets and models for a comprehensive understanding of their impact on the carbon cycle. • Biocrusts increase soil CO2 efflux by 66.5 g C m-2yr-1 in drylands worldwide. • Climate warming increases CO2 efflux in biocrust soil by 22.9 g C m-2yr-1 per °C. • Thermal adaptation reduces thermal sensitivity of biocrust carbon efflux. [ABSTRACT FROM AUTHOR]

• BSCs enhanced the recovery of nutrient levels of surface dune soil over a 50-year revegetation. • Nutrient enrichment rate (NER) of BSCs exhibited patterns. • Year 31 was a key turning point for development of BSCs. • Nutrient levels were affected by both soil conditions and biological properties of cryptogams. Revegetation, an effective method for restoring desertified lands, helps enhance the colonization and development of biological soil crusts (BSCs) and improves the nutrient conditions of desert soils. This study aims to shed light on the changes of elemental concentrations and their enrichment in fixed surface soil of sand dunes over a 50-year revegetation chronosequence linked to BSCs of different successional stages in the Tengger desert of China. We investigated the elemental levels of K, Na, Ca, Mg, Mn, Zn, Cu, and Fe in surface soil covered by cyanobacteria-lichen crusts, moss crusts and subsoil. Nutrient enrichment of BSCs and soils were analyzed to reflect the nutrient changes in the revegetated desert ecosystem. Concentrations of K, Na, Ca, Mn, Zn, and Cu in cyanobacteria-lichen crusts were significantly higher than in mobile sand dunes. Nutrient enrichment rate (except for Na) exhibited unimodal patterns, and year 31 was a key turning point after which the rate switched from increasing to decreasing over time. Our long-term study indicated that both cyanobacteria-lichen crusts and moss crusts can effectively improve nutrient accumulation and promote edaphic conditions, which is beneficial to the development and nutrient cycling of desert ecosystems. [ABSTRACT FROM AUTHOR]

Global climate change influences not only vascular plants, but also biological soil crusts (biocrusts), which play important roles in dryland vegetation dynamics by redistributing rainfall in soils. Different types of biocrusts, spanning a spectrum from cyanobacteria-dominated and moss-dominated, have distinct roles in rainfall redistribution patterns, but the ecohydrological effects of different biocrust types on dryland ecosystem dynamics remain largely unclear. This study developed an ecohydrological model with biocrust as a system state variable to explicitly explore the effects of different biocrust types on dryland vegetation dynamics in Shapotou region in northern China, particularly after restoration. The results indicated that both cyanobacteria- and moss-dominated biocrusts could support high grass cover (approximately 40%) after restoration. Cyanobacterial, but not moss biocrusts, could also maintain a high level of shrub cover (13 and 3%, respectively). Shifting from cyanobacteria to mosses gradually increased the biocrust cover from approximately 40% to 80%. The biocrust's water-holding capacity (the volume of water it can intercept per unit area) is likely be able to explain the dynamics of biocrust and shrub cover (with correlation efficiency of R2 = 0.972 and 0.987, respectively), but not grass cover (R2 = 0.224). The findings suggest that biocrust type may significantly affect coverage of biocrusts and shrubs, but not grass coverage, and global climate change may influence dryland restoration by altering biocrust types. Unlabelled Image • Biocrust in early-stage succession can support high cover for both grasses and shrubs. • Biocrust in late-stage succession maintains high grass cover, while not shrub cover. • Biocrust cover increases gradually as biocrust type shifting from early- to late-stage. • We explored ecohydrological mechanisms to interpret the changes in vegetation cover. • Climate change may influence dryland restoration in a way of altering biocrust type. [ABSTRACT FROM AUTHOR]

Reconstructing vegetation in arid and semiarid areas has become an increasingly important management strategy to realize habitat recovery, mitigate desertification and global climate change. To assess the carbon sequestration potential in areas where sand-binding vegetation has been established on shifting sand dunes by planting xeric shrubs located near the southeastern edge of the Tengger Desert in northern China, we conducted a field investigation of restored dune regions that were established at different times (20, 30, 47, and 55years ago) in the same area. We quantified the total organic carbon (TOC) in each ecosystem by summing the individual carbon contributions from the soil (soil organic carbon; SOC), shrubs, and grasses in each system. We found that the TOC, as well as the amount of organic carbon in the soil, shrubs, and grasses, significantly increased over time in the restored areas. The average annual rate of carbon sequestration was highest in the first 20years after restoration (3.26×10−2 kg·m−2·year−1), and reached a stable rate (2.14×10−2 kg·m−2·year−1) after 47years. Organic carbon storage in soil represented the largest carbon pool for both restored systems and a system containing native vegetation, accounting for 67.6%–85.0% of the TOC. Carbon in grass root biomass, aboveground grass biomass, litter, aboveground shrub biomass, and shrub root biomass account for 10.0%–21.0%, 0.2%–0.6%, 0.1%–0.2%, 1.7%–12.1% and 0.9%–6.2% of the TOC, respectively. Furthermore, we found that the 55-year-old restored system has the capacity to accumulate more TOC (1.02kg·m−2 more) to reach the TOC level found in the natural vegetation system. These results suggest that restoring desert ecosystems may be a cost-effective and environmentally friendly way to sequester CO2 from the atmosphere and mitigate the effects of global climate change. [ABSTRACT FROM AUTHOR]

Abstract: Revegetation is a common method to combat desertification and to reduce soil carbon loss in arid and semi-arid areas worldwide. Revegetated areas in the temperate arid Shapotou area of Northern China were established to stabilize sand dunes in an area subject to wind erosion. The objective of this study was to characterize the carbon flux of a 20-year old revegetated area. During the measurement period from May 2008 to December 2010 carbon flux was measured by the eddy covariance technique, and rainfall, temperature, and soil water content were monitored simultaneously with the aim of understanding the relationship between carbon flux and meteorological factors. We found that the revegetated ecosystem is a carbon sink during the growing season when most of the annual precipitation falls. The revegetated area changed from being a carbon source to a sink in the 1 or 2 days following an effective rainfall event. In the non-growing season the ecosystem was a carbon source. The soil water content (SWC) affected the relationship between ecosystem respiration and temperature. The nighttime respiration rate increased with soil temperature. When the SWC was ≥3% the correlation between respiration rate and soil temperature was stronger (R 2 =0.23) than when SWC was <3% (R 2 =0.08). Although the net ecosystem carbon flux (NEE) in temperate arid desert areas is relatively small compared to that of humid areas, it represents huge carbon fixation potential because of the very large area of desert in northern China. Further research is required to clarify the effects of climatic factors on the various components of temperate arid ecosystems, especially the roles of cryptogam and biological soil crusts in the carbon exchange processes. [Copyright &y& Elsevier]