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Warming and precipitation fluctuations are changing desert ecosystems in global drylands. However, the effects of climate change on keystone species such as cryptogamic biocrust in drylands remain relatively under‐investigated, even though biocrusts play a vital role in desert ecosystems.We conducted a long‐term experiment (14 years) to simulate the responses of two main types of biocrusts to warming coupled with reduction in precipitation that was achieved by open‐top chambers (OTCs) to simulate the predicted warming and precipitation decreasing under climate change scenario. We also conduct a structural analysis to evaluate the resulting changes in desert ecosystem functioning (carbon and nitrogen cycling).Neither warming and corresponding rainfall reduction treatments had a negative effect on lichen species richness, but both treatments reduced lichen cover and biomass. The negative effects of warming on moss‐dominated crusts were much greater than those on lichen‐dominated crusts. Although mosses and lichens had varying degree responses to warming, the loss of mosses and decreased lichen cover and biomass, as well as the shortening of the wet time, resulted in a reduction in carbon and nitrogen fixation, soil enzyme activity and water‐holding capacity of biocrusts and topsoil. These impacts collectively change the water balance of drylands and weaken the hydrological and biogeochemical function of biocrusts.Synthesis and applications: Results from this long‐term experiment suggest that the ecosystem C and N cycling and water balance of global drylands may be highly impacted by climate change, in part because of the response of biocrusts, which contribute an important implication for both dryland restoration and earth system dynamics. [ABSTRACT FROM AUTHOR]

Purpose: The influences of biological soil crusts (BSCs) on soil properties have been investigated extensively. However, few studies have compared soil properties under different types of BSCs in different erosion regions. Methods: Three erosion regions (water erosion, wind-water crisscross erosion, and wind erosion regions) were identified in the Loess Plateau, and we collected subsoil samples of cyanobacteria and moss crusts in each region (crust coverage > 95%), respectively. The variations of soil nutrient content and enzyme activity were evaluated, and the most influential soil properties were determined. Results: Most of the tested soil properties were significantly affected by erosion and crust types (p < 0.05). Soil pH was significantly higher, while soil electrical conductivity (EC) was substantially lower in the water erosion region than the water-wind crisscross erosion and wind erosion regions (p < 0.05). Soil nutrient content and enzyme activity were higher in the water erosion region compared to the wind erosion and wind-water erosion regions (p < 0.05). In the subsoil below BSCs, most of the soil nutrient availability and enzyme activity was higher under moss crusts than cyanobacteria crusts (p < 0.05). Conclusion: Our results suggested that there were differences in the effects of two types of BSCs on the soil nutrient availability and enzyme activity across the three typical erosion regions in the Loess Plateau, and the magnitude of these effects followed the order of: water erosion regions > wind erosion regions > wind-water erosion crisscross regions, and moss crusts > cyanobacteria crusts. [ABSTRACT FROM AUTHOR]

Desert ecosystems are generally considered lifeless habitats characterised by extreme environmental conditions, yet they are successfully colonised by various biocrust nonvascular communities. A biocrust is not only an important ecosystem engineer and a bioindicator of desert ecological restoration but also plays a vital role in linking surficial abiotic and biotic factors. Thus, extensive research has been conducted on biocrusts in critical dryland zones. However, few studies have been conducted in the vast temperate deserts of China prior to the beginning of this century. We reviewed the research on biocrusts conducted in China since 2000, which firstly focused on the eco-physiological responses of biocrusts to species composition, abiotic stresses, and anthropological disturbances. Further, research on the spatial distributions of biocrusts as well as their succession at different spatial scales, and relationships with vascular plants and soil biomes (especially underlying mechanisms of seed retention, germination, establishment and survival of vascular plants during biocrust succession, and creation of suitable niches and food webs for soil animals and microorganisms) was analysed. Additionally, studies emphasising on the contribution of biocrusts to ecological and hydrological processes in deserts as well as their applications in the cultivation and inoculation of nonvascular plants for land degradation control and ecological restoration were assessed. Finally, recent research on biocrusts was evaluated to propose future emerging research themes and new frontiers. [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]

Aims: In water-limited areas, shrubs influence biological soil crust (biocrust) composition and diversity via soil microenvironment alterations and through modifying biotic interactions amongst biocrust taxa. However, the relative contributions of shrubs to biocrust succession and assembly via the biotic and abiotic influences are poorly known. Methods: The community composition of biocrusts and soil properties in the interspace and beneath the dominant shrub (Artemisia ordosica) along a biocrust succession sequence were investigated. Biocrust interspecific interactions at a small scale (within shrub) were evaluated based on the co-occurrence pattern using null models. A hypothetical multigroup structural equation model (SEM) was proposed to evaluate the influence of multiple variables on the biocrust richness and to investigate the path variance between successional stages. Results: Along the biocrust succession, shrubs significantly increased the size of bare soil gap by 489%, decreased lichens by 43% and increased soil organic matter by 13%. In years 18, 31and 37, the paths in SEM explained 59% of the variation in richness, only the effect of abiotic amelioration was significant (0.62). In years 54 and 62, the shrubs had direct (0.37) and indirect effect (0.10) via species interaction to biocrust richness. Conclusions: Shrubs directly and indirectly affected the community assembly of biocrusts. Biocrust species interactions are an important driver of biocrust diversity and primarily affect late succession. The increasing influences of shrubs suggests a close relationship between shrub and biocrust components in arid or semiarid ecosystems, with shrubs playing an important role in regulating biocrust assembly and maintaining biocrust richness. [ABSTRACT FROM AUTHOR]

Aims: Biological soil crusts (BSCs) are widely considered critical for soil fertility in arid ecosystems. However, how microbial communities regulate the C and N cycles during BSC succession is not well understood. Methods: We utilized GeoChip 5.0 to analyze the functional potential of bacteria and fungi involved in the C and N cycles of BSCs along a 61-year revegetation chronosequence. Results: The normalized average signal intensities of different functional genes involved in C and N metabolism in 61-year-old BSCs were significantly different from those in younger BSCs and most functional gene subcategories and the corresponding dominant functional populations were derived from bacterial rather than fungal communities. Most C degradation genes (dominated by the starch-degrading gene amyA) were derived from Actinobacteria (mainly Streptomyces) in bacteria, but Ascomycota (mainly Aspergillus) was the key population for lignin degradation (dominated by the phenol oxidase gene) during BSC succession. N cycle genes involved in denitrification (such as narG, nirK/S, and nosZ) and N fixation (nifH) were mainly derived from Unclassified Bacteria, whereas genes involved in ammonification (ureC) were mainly derived from Streptomyces. Moreover, redundancy analysis showed that soil biogeochemical properties were closely related to bacterial and fungal functional gene structures during BSC succession. Conclusions: These findings indicate that bacteria play a crucial role in the regulation of C and N cycles during BSC succession in arid ecosystems, while fungi perform supplementary degradation of lignin, and these communities can successfully stimulate an increase in C and N metabolism in soil during the later successional stages of BSCs. [ABSTRACT FROM AUTHOR]

Background and aims: Despite the important role of biological soil crusts in the soil carbon cycles of desert ecosystems, the responses of soil respiration in biological soil crust-dominated areas to warming are not well understood. The goal of this study was to investigate the expected increases in temperature on soil respiration both diurnally and seasonally in biological soil crust-dominated areas. Methods: We used open-top chambers to simulate warming in the Shapotou region in the Tengger Desert, northern China. An automated soil respiration system was used to measure the soil respiration rates in moss-dominated crusts. The measured environmental variables included the precipitation, volumetric soil water content, air temperature and soil temperature at depths of 0, 5, 10, 20, and 50 cm. Results: The response of soil respiration to warming is a function of soil moisture following rainfall in desert ecosystems. Our results showed that 1.5 °C of simulated warming significantly decreased soil respiration, indicating that the inhibition of soil respiration was likely due to the reduction in soil water content at a relatively high temperature. Over daily cycles, hourly soil respiration rates have commonly been related to hourly temperatures. The observed diel hysteresis between hourly soil respiration and temperature resulted in semielliptical hysteresis loops, and the temperature often lagged behind soil respiration for several hours. The lag times between soil respiration and temperature were significantly and positively related to the depth of the soil temperature measurements. The proximate reason for the diel hysteresis between soil respiration and temperature was likely a mismatch between the depth of CO2 production and the depth of the temperature measurements. Conclusions: Our results indicate that warming increases the response of soil respiration to soil water availability in biological soil crust-dominated desert ecosystems. Therefore, the accelerated drying effect of warming on soil respiration and diel soil respiration patterns between soil respiration and temperature at different depths should be considered in future soil carbon cycle models for biological soil crust-dominated desert ecosystems. [ABSTRACT FROM AUTHOR]

Soil respiration induced by biological soil crusts (BSCs) is an important process in the carbon (C) cycle in arid and semi-arid ecosystems, where vascular plants are restricted by the harsh environment, particularly the limited soil moisture. However, the interaction between temperature and soil respiration remains uncertain because of the number of factors that control soil respiration, including temperature and soil moisture, especially in BSC-dominated areas. In this study, the soil respiration in moss-dominated crusts and lichen-dominated crusts was continuously measured using an automated soil respiration system over a one-year period from November 2015 to October 2016 in the Shapotou region of the Tengger Desert, northern China. The results indicated that over daily cycles, the half-hourly soil respiration rates in both types of BSC-covered areas were commonly related to the soil temperature. The observed diel hysteresis between the half-hourly soil respiration rates and soil temperature in the BSC-covered areas was limited by nonlinearity loops with semielliptical shapes, and soil temperature often peaked later than the half-hourly soil respiration rates in the BSC-covered areas. The average lag times between the half-hourly soil respiration rates and soil temperature for both types of BSC-covered areas were two hours over the diel cycles, and they were negatively and linearly related to the volumetric soil water content. Our results highlight the diel hysteresis phenomenon that occurs between soil respiration rates and soil temperatures in BSC-covered areas and the negative response of this phenomenon to soil moisture, which may influence total C budget evaluations. Therefore, the interactive effects of soil temperature and moisture on soil respiration in BSC-covered areas should be considered in global carbon cycle models of desert ecosystems. [ABSTRACT FROM AUTHOR]

In arid and semiarid ecosystems, the potential threats of exotic invasive species are enhanced due to increasing human activities. Biological soil crusts ( BSCs), acting as arid ecosystem engineers, may play an important role in preventing the establishment of exotic invasive plants. Our goal was to examine whether BSCs could inhibit the establishment of probable exotic plant species originating from adjacent grasslands located along the southeast edge of the Tengger Desert. In our study, we investigated the effects of three BSC types (cyanobacteria, lichen, and moss crusts) under two disturbance conditions (intact and disturbed) on the establishment of two exotic plant species ( Ceratoides latens and Setaria viridis) using indoor experiments. We found both negative and positive effects of BSCs on the establishment of the two exotic plant species. Compared with the disturbed BSCs, the germination percentages of C. latens and S. viridis were reduced by 54% to 87% and 89% to 93%, respectively, in intact BSCs. In contrast, BSCs significantly promoted the height growth and aboveground biomass of the two exotic plant species ( p < .05) by enhancing the soil water and nutrient availability for the exotic plants. Our results confirm that BSCs strongly suppress the rapid expansion of exotic plant populations by inhibiting germination of seed with big size or appendages and have a weak inhibitory effect on exotic plant with small and smooth seeds. This may decrease the threat of propagation of exotic species. In the meantime, BSCs promote the growth of a few successful engraftment seedlings, which increased the beta diversity. Our work suggests that better understanding the two opposing effects of BSCs on the establishment of exotic plant species in different growth stages (germination and growth) is important for maintaining the health and stability of revegetated regions. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) can improve the stability and health of native plant communities in arid ecosystems. However, it is unknown whether BSCs can also inhibit invasions of exotic vascular plants on stabilized reclaimed sand dunes. To answer this question, we conducted a greenhouse experiment to test the effects of cyanobacteria-dominated BSCs on 1) seed germination and biomass of an exotic grass (Stipa glareosa P. Smirn.), and 2) individual biomass of the exotic S. glareosa growing with two native plants, Eragrostis poaeoides Beauv. and Artemisia capillaris Thunb. Our experiment included three BSC treatments (intact crust, disturbed crust, and bare soil) and five species trials (native E. poaeoides alone, E. poaeoides mixed with exotic S. glareosa, native A. capillaris alone, A. capillaris mixed with exotic S. glareosa, and S. glareosa alone). The results showed that cyanobacteria-dominated crusts can significantly reduce the cumulative percent germination of the exotic grass (P<0.001) and native plants (P<0.001). Maximum cumulative percent germinations of the exotic grass and two native plants were found in bare soil, and minimum in intact crusts. The interaction of crust treatment × species trials on shoot biomass of the two native plants was significant (P<0.05). These results indicate that the presence of BSCs on stabilized sand dunes may reduce the germination of the exotic and two native plants. The effect of reducing exotic and native plant seeds germination would maintain more diverse plant communities and contribute to the formation of clumped vegetation patterns. We conclude that BSCs act as a natural regulator for vegetation patterns and thus promote ecosystem stability and sustainability. [ABSTRACT FROM AUTHOR]

• NAs of cyanobacteria- and moss-dominated crusts respond differently to warming. • Lower warming increased N input in cyanobacteria-dominated crusts. • Higher warming decreased N input in soils of both biocrusts. Changes in temperature and precipitation are expected to influence the function of desert ecosystems by altering the biogeochemical cycles of elements. Biocrusts can introduce additional nitrogen (N) and carbon (C) to arid ecosystems through N fixation and photosynthesis. Although biocrusts are the main N contributor in desert ecosystems, it remains unclear how the nitrogenase activity (NA) of biocrusts responds to the prolonged warming coupled with precipitation reduction that is predicted to occur with climate change. To address this important knowledge gap, the experiment including two groups of open-top chambers was designed to simulate the predicted climate change in an arid desert. In a simulation experiment conducted over 14 years, the NAs of cyanobacteria- and moss-dominated crusts were determined by acetylene reduction assay. In parallel, the water increment, NO 3 –-N, NH 4 +-N, total N content, and absolute abundance of nif H-gene were also determined. The results showed that in cyanobacteria-dominated crusts, 0.5 °C-warming coupled with a reduction in precipitation (abbreviated as 0.5 W-RP) increased the NA, while 1.5 °C-warming coupled with a reduction in precipitation (1.5 W-RP) decreased the NA and the biocrust-soil total N content. The abundance of nif H-gene in the cyanobacteria-dominated crusts increased under the two warming scenarios. Both 0.5 W-RP and 1.5 W-RP promoted the NA in the moss-dominated crusts, simultaneously reducing the abundance of nif H-gene. However, there was no N pool increase in the cyanobacteria-dominated crusts with 1.5 W-RP and in the moss-dominated crusts under the two warming scenarios. In contrast, the results suggested that there may be an increase in nitrogen input in cyanobacteria-dominated crusts under lower warming. [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]

• The responses of dominant species in biocrust communities to warming are variable. • Warming significantly reduced the carbon uptake of the moss-dominated crusts. • Coupled warming and drought are likely to increase the dominance of lichens in biocrust. Global warming coupled with increased drought is predicted to have a significant negative impact on desert ecosystems. In arid desert regions, a large proportion of the ground surface is covered by specialized organisms such as mosses and lichens that form biocrusts, which play a vital role in ecosystems. However, the long-term effects of warming and drought on these key biotic components of desert ecosystems remain poorly understood. Using a manipulative experiment conducted for 12 years in the Tengger Desert, northwestern China, we evaluated how both mosses and lichens in biocrust communities responded to 0.5°C and 1.5°C increases in temperature coupled with 5% and 8% reductions in total annual precipitation, respectively, using two groups of open-top chambers to approximate climate change conditions that are predicted to occur in this study region. Furthermore, surface soil carbon uptake by the biocrusts was also evaluated. Twelve years of warming coupled with increased drought resulted in a significant decrease in the cover and biomass of mosses but did not change the cover or biomass of lichens. These changes in the mosses were positively correlated with the duration and intensity of the treatments. Warming coupled with reduced precipitation significantly reduced the carbon uptake of the moss-dominated biocrusts by reducing the availability of moisture content. However, lichen carbon uptake was insensitive to the warming and reduced precipitation treatments. The reduction in cover and biomass of moss-dominated biocrusts might be attributed to large amounts of carbon loss, which further alters biocrust multifunctionality in desert ecosystems. In addition, our findings suggest that coupled warming and drought conditions could increase the dominance of lichens in biocrust communities to partly maintain the multifunctionality of biocrusts in this desert ecosystem. [ABSTRACT FROM AUTHOR]

[Display omitted] • Abundant, intermediate and rare bacteria exhibit distinct succession patterns in BSCs. • Positive rather than negative correlations were predominantly in BSC bacterial networks. • Most of the keystone taxa in BSC bacterial networks were rare bacteria. • The AB, IB and RB communities responded differently to environmental variables. • The diversity of ABs, IBs and RBs was key drivers of BSC bacterial network properties. The bacterial communities of biological soil crusts (BSCs) often comprise abundant, intermediate and rare taxa that form complex ecosystems through interspecies interactions and play essential roles in regulating the process of vegetative restoration. However, the community structure of nonabundant bacteria and the interactions among these abundance categories are still largely unknown. In light of this, we used Illumina MiSeq sequencing to investigate the succession characteristics and co-occurrence patterns of abundant bacteria (ABs), intermediate bacteria (IBs) and rare bacteria (RBs) in the three developmental stages of BSCs (cyanobacteria-, lichen- and moss-dominated crusts) on the southeastern edge of the Tengger Desert. The results showed that the changes in the Chao richness and taxonomic composition of ABs, IBs and RBs were significantly different during BSC succession. The results of the co-occurrence network analysis revealed that most of the observed associations were between RBs (more than 80 %), positive correlations were predominant (more than 77 %), and the vast majority of the keystone taxa in the BSC bacterial networks were RBs (only one belonged to IBs). Moreover, the driving effects of environmental variables on ABs, IBs and RBs were not exactly the same, and their diversity was a key driver of the co-occurrence network properties of the BSCs. These findings are crucial for understanding the establishment and maintenance of BSC bacterial diversity and provide a new perspective for utilizing microbial resources and/or regulating environmental factors to achieve the sustainable development of desert ecosystems. [ABSTRACT FROM AUTHOR]

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]

Biological soil crusts (BSCs), the pioneers of restoration of degraded vegetation, act as an organizing principle in drylands largely through metabolic activities of microbial communities. However, little is known about the microbial functional potential involved in biogeochemical processes during BSC succession in desert ecosystems. Here, we utilized a functional gene array (GeoChip 5.0) in conjunction with determinants of microbial community compositions of BSCs along a revegetation chronosequence in the Tengger Desert, to address the following: (a) how the functional structure of the microbial community changes with BSC age in different soils and (b) how genes involved in carbon (C)- and nitrogen (N)-cycling change and whether they promoted an increased microbial metabolic potential during BSC succession in desert revegetation. The results showed that the relative abundance of functional genes was determined by the microbial community compositions in the BSC development process, and the significant differences in microbial functional genes were detected in 61-year-old BSCs from other aged BSCs. Redundancy analysis indicated that the abundance of fungi and moss and soil physicochemical properties were the important factors determining differences in microbial functional structures. Functional genes associated with C degradation and N denitrification were the major components involved in C and N cycles, which were closely related to the increased fungal abundance during succession. The increased gene abundance of 61-year-old BSCs in both C and N cycles promoted microbial metabolic potential. These results indicated that fungi might be the key microbial mediators in C and N cycling in the later development of BSCs, and microbial functional structure could be a potential indicator of revegetation sustainability in desert ecosystems. Highlights • The microbial functional structure differs in 61-year-old BSCs from others. • Genes in C and N cycles were mainly focused on C degradation and N denitrification. • Fungi might be the key microbial mediators in C and N cycling after 61 years succession. • The increased gene abundance promoted microbial metabolic potential. • Microbial functional structure could be a potential indicator of revegetation sustainability. [ABSTRACT FROM AUTHOR]

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

Microbial communities play a very important role in soil ecological processes by regulating biogeochemical cycles during biological soil crust (BSC) succession in desert ecosystems. Although the relationships between microbial carbon or nitrogen and the BSC at different successional stages have been a source of great concern, there are few reports regarding the phosphorus (P) and sulfur (S) cycles. In this study, we used a functional gene array (GeoChip 5.0) to analyze the characteristics of microbial communities and their functional genes involved in the P and S cycles along a chronosequence of BSC succession in the Tengger Desert, China. The results showed that the functional genes associated with polyphosphate degradation and sulfite reduction were the major components involved in the P and S cycles, respectively, and the intensities of the functional genes expression involved in the P and S cycles increased significantly in 61-year-old BSCs. Compared with the fungal and archaeal communities, the bacterial community was the major contributor to the P and S cycles, and Proteobacteria (mainly Alphaproteobacteria, Gammaproteobacteria, and Betaproteobacteria) and Actinobacteria were the dominant phyla. A redundancy analysis showed that there was significant synergy between the improvement in soil properties (e.g., soil nutrient content) and the intensities of genes expression related to P and S cycles. These findings indicated that after 61 years, BSC significantly promoted the microbial metabolic potential for P and S cycling, which in turn promoted soil rehabilitation in a desertified dryland. • Polyphosphate degradation and sulfite reduction were the major metabolism processes involved in the P and S cycles in BSCs. • The intensity of gene expression involved in P and S cycles increased significantly in 61-year-old BSC. • Bacterial community was the major contributor to the P and S cycles of BSCs compared to fungi and archaea. [ABSTRACT FROM AUTHOR]

• Soil respiration in BSC-dominated areas was suppressed under warmer conditions. • The inhibited soil respiration by warming was greater on the moss than lichen crust. • Soil respiration in BSC-dominated areas was significantly induced by rainfall pulses. • Diel hysteresis between soil respiration and temperature was modified by rainfall. Biological soil crusts (BSCs) across desert ecosystems play an important role in modulating terrestrial carbon cycles. Global warming and changes in precipitation patterns are expected to be important triggers for biological activity in BSC-dominated desert ecosystems. Therefore, it is crucial to study the effects of warming and rainfall pulses on soil respiration dynamics at BSC-dominated microsites to predict terrestrial carbon cycling under climate change. In this study, soil respiration rates were monitored continuously during three types of natural precipitation events in lichen-dominated and moss-dominated crusts in both control and warming treatments. Our results revealed that soil respiration was inhibited in BSC-dominated microsites in the warming treatment because of reduced soil water content induced by the warmer conditions, and that the extent of inhibition was lower in the lichen-dominated crusts than in the moss-dominated crusts. During all the precipitation events, soil respiration rates were significantly increased by rainfall pulses and gradually declined thereafter. Over the daily cycle, the clockwise diel hysteresis loop between soil respiration and soil temperature was modified by soil water availability, which was affected by the magnitude of rainfall pulses. Moreover, the effect of photosynthetically active radiation and the mismatch between the depth of carbon dioxide (CO 2) production and soil temperature measurement may have contributed to the diel hysteresis pattern. Our results indicated that warming and different types of precipitation events in BSC-dominated desert ecosystems impact soil carbon release through changes in the magnitude of soil respiration. [ABSTRACT FROM AUTHOR]

• Archaeal community and functional structures were studied during BSC succession. • Archaeal diversity, abundance, and functional gene intensity were highest in the initial stage. • The dominant phyla of archaea were complementary in biogeochemical cycles. • C:N ratio was the mainly limited factor for archaeal diversity and function. • Archaea might serve as a pioneer species of microbial communities in BSC development. Archaea are major contributors to biogeochemical cycles and energy metabolism among soil microorganisms under extremely acidic and high-temperature conditions, however, the biodiversity and ecological function of archaea in biological soil crusts (BSCs) of desert ecosystems are not fully understood. Here, we used Illumina MiSeq sequencing and microbial functional gene array (GeoChip 5.0) to test the following hypotheses: (1) the composition and function related to biogeochemical cycles of the archaeal community would change significantly in the development process of BSCs; and (2) the key factors driving these changes may be soil biogeochemical properties. The results showed that the diversity, abundance, and functional potential of the archaeal community showed their highest levels in 5-year-old BSCs. The dominant phyla were Thaumarchaeota, Euryarchaeota, and an unclassified phylum in the archaeal community during BSC succession. The functional genes of the archaeal community were mainly involved in carbon (C) and nitrogen (N) cycles, and the functions of the three dominant phyla were complementary in these cycles. Moreover, redundancy analysis showed that soil biogeochemical properties were negatively related to the composition and function of the archaeal community during BSC succession, and the soil C:N ratio might be the major limiting factor. These results provided evidences for our hypotheses and revealed that the archaeal community played an important ecological role in the early development stage of BSCs, and might be pioneer species of soil microbial communities during BSC succession. [ABSTRACT FROM AUTHOR]