Biological soil crusts (BSCs) are important components of dryland soils that influence nutrient cycling and soil microbial activity, yet the depth-dependent responses of BSCs-associated microbial communities to long-term nitrogen (N) enrichment remain insufficiently understood. Here, we conducted a 13-year in situ N addition experiment (0–3.0 g N m⁻² yr⁻¹) in the Gurbantunggut Desert to compare bacterial and fungal communities between the moss BSCs layer and the underlying sub-biocrust soil (0–5 cm). Microbial communities exhibited pronounced vertical differentiation, with higher bacterial and fungal biomass and higher bacterial diversity in the BSCs layer than in sub-biocrust soils. Long-term N addition produced strong depth- and taxon-dependent responses. In the BSCs layer, bacterial communities were more sensitive to N addition than fungal communities, showing reduced niche breadth and migration-related parameters and a shift in community assembly from stochastic toward deterministic processes, accompanied by decreased co-occurrence network robustness. In contrast, fungal communities in sub-biocrust soils responded more strongly than bacteria, where N addition similarly promoted deterministic succession and reduced network robustness. Structural equation modeling further indicated that N influenced microbial communities in the BSCs layer via both direct effects and indirect effects mediated by changes in soil nutrient availability, whereas responses in sub-biocrust soils were entirely nutrient-mediated. Overall, these results demonstrate that long-term N addition induces depth-dependent changes in microbial community assembly and association network structure in BSCs-associated soils, highlighting the importance of accounting for soil depth and microhabitat heterogeneity when evaluating the impacts of N enrichment on dryland soil microbial communities and nutrient cycling.

Aridity represents a primary driver of desertification in semiarid and arid ecosystems, where soil microbial communities play pivotal roles in sustaining dryland ecosystem functions. However, the mechanisms by which biocrust-forming mosses influence bacterial community distribution and assembly under varying levels of aridity remain insufficiently resolved. In this study, we investigated the effects of moss crusts on bacterial community diversity and assembly processes across arid and semiarid regions of northern China using targeted metagenomic analysis of the 16S rRNA gene. Our results show that moss crusts significantly enhance bacterial alpha-diversity while reducing beta-diversity relative to adjacent bare soil across all sampled regions. Moreover, bacterial communities associated with moss crusts exhibit a stronger propensity for stochastic assembly processes compared to those in bare soils, and display attenuated spatial turnover along the aridity gradient. In contrast, bacterial assembly in bare soils is jointly constrained by aridity and soil nutrient availability, whereas moss crust-associated communities are predominantly influenced by aridity. Notably, moss crusts elevate the aridity threshold under which bacterial community assembly transitions from stochastic to deterministic dominance, from 0.83 to 0.91, thereby extending the range of aridity conditions under which stochastic processes prevail. These findings highlight the critical role of moss crusts in enhancing the functional stability of desert ecosystems under drought stress, through modulation of regional-scale bacterial diversity, heterogeneity, and assembly dynamics, and support their strategic application in climate-resilient ecological restoration.

Grassland ecosystems play a crucial role in the global carbon cycle, yet the spatial patterns and drivers of soil organic carbon density (SOCD) across aridity gradients remain insufficiently understood. Here, we used the Carbon Density Dataset of China's Terrestrial Ecosystems (2010s) and applied random forest models to simulate SOCD at two soil depths (SOCD0-20 cm and SOCD0-100 cm) in arid and humid grasslands. We further quantified the contributions of environmental drivers and projected future SOCD dynamics under Shared Socioeconomic Pathways (SSPs). Results showed that SOCD was lower in arid than in humid regions, but due to their vast extent, arid regions contained larger total soil carbon stocks. The 0-20 cm layer accounted for approximately 50% of the SOCD in the 0-100 cm profile. In arid regions, SOCD0-20 cm was mainly controlled by mean annual temperature and soil moisture, while SOCD0-100 cm depended on clay content and total nitrogen. In humid regions, SOCD0-20 cm was strongly influenced by temperature and NDVI, whereas SOCD0-100 cm was regulated by clay and nitrogen. Under future SSP scenarios, SOCD is projected to decline in arid regions but increase in humid regions, indicating an enhanced carbon sink potential. SOCD0-20 cm showed higher variability and lower stability than SOCD0-100 cm. These findings clarify the spatial heterogeneity and depth-dependent controls of grassland SOCD and provide a scientific basis for region-specific soil carbon management, contributing to China's "dual carbon" goals and sustainable grassland policies.

Biological soil crusts (biocrusts) are essential for nitrogen (N) cycling in arid ecosystems, but how snow cover modulates these processes remains unclear. This study investigated the effects of variable snow cover on N fixation, ammonia oxidation (AO), and microbial networks across moss-, lichen-, and cyanobacteria-dominated biocrusts in China's Gurbantunggut Desert. Snow manipulations double snow (DS), ambient snow (CK), and removed snow (RS) were applied to biocrust plots in winter. Nitrogen fixation and AO rates, soil properties soil water content (SWC), organic carbon (SOC), inorganic N, and microbial co-occurrence networks were analyzed in spring. DS enhanced nitrogen fixation rates, particularly in cyanobacteria-dominated crusts (up to 0.4 μg N g-1 day-1), while moss crusts showed elevated fixation under RS conditions (rates can up to 0.4 μg N g-1 day-1), which correlated with increased SWC (r = 0.72) and SOC (r = 0.65). Conversely, RS reduced AO rates by 50-67 % across biocrusts, with cyanobacteria experiencing the steepest decline (20 μg N g-1 day-1). Microbial networks under DS exhibited higher modularity in moss crusts (modularity = 0.85), indicating structured, cooperative communities, while RS fragmented networks, especially in cyanobacteria (modularity = 0.41). Soil salinity (EC) and pH were negatively correlated with microbial activity under RS. Moss crusts showed resilience, maintaining stable N fixation and microbial diversity under varying snow cover, whereas cyanobacteria showed increased sensitivity to drought. These results highlight the critical role of snow cover in maintaining N cycling during the spring season via moisture retention and SOC accumulation. Declining snow cover, as predicted under climate change, may disproportionately affect cyanobacteria-dominated crusts and thus destabilize soil fertility. Conservation strategies that prioritize bryophyte biocrusts could enhance ecosystem resilience in arid landscapes. This study highlights the interplay between snow regimes, biocrust type, and microbial functionality, and provides insights for predicting N cycling dynamics in warming drylands.

Phyllosphere microorganisms play a vital role in enhancing the adaptability and functionality of their host plants. Although the effects of phyllosphere microbial communities on host functional traits and their association with host phylogeny has been widely investigated, it remains unclear whether host selection consistently drives the assembly of these communities. In this study, bacterial and fungal communities on the surfaces of 734 leaf samples were characterized using bacterial and fungal amplicon sequencing. These microbial communities were associated with 42 plant species native to the Gurbantunggut Desert, a representative temperate desert located in Central Asia. The research assessed the relative contributions of plant-related factors, abiotic environmental variables (such as climate and soil), and spatial components to the observed variation in phyllosphere microbial communities, and further inferred the topological structure of plant-microbe interaction networks. The results indicate that plant phylogeny, plant functional traits, abiotic environment conditions, and spatial factors account for variations in the bacterial community composition (36.4 %, 4.6 %, 1.0 %, and 0.1 %, respectively) and the fungal community composition (28.6 %, 3.0 %, 1.5 %, and 1.2 %, respectively), following a hierarchical trend of plant phylogeny > plant functional traits > abiotic environment > space. Plant phylogeny and functional traits play a central role in shaping the assembly of phyllosphere microbial communities, indicating that plant filtering effects significantly influence microbial composition. Analysis of plant-microbe interactions reveals distinct preferences of microbial taxa for plant hosts across different taxonomic levels and geographic regions. Bipartite network analysis further illustrates that plant-microbe networks are highly specialized and modular, with plant-fungal networks exhibiting greater host specificity compared to plant-bacterial networks. Collectively, these findings underscore plant filtering as the primary determinant of microbial community assembly in the desert phyllosphere and provide valuable insights into the macroecological patterns shaping plant-microbe interactions in arid ecosystems.

During periods with no precipitation, desert ecosystem soils periodically absorb air moisture at night to form non-rainfall water inputs (NRWIs), while substantial carbon dioxide (CO2) emissions are typically observed during midday. However, the intrinsic relationship between these periodic NRWIs and the CO2 release phenomenon remains unclear. In this study, we utilized biological soil crusts and employed in situ observation methods during the summer and fall. We also conducted humidity- and temperature-controlled experiments to investigate the effects and potential mechanisms of NRWIs and temperature variations on daily soil CO2 release. We found that soil accumulated NRWIs and soil respiration rates reached their peak values at dawn and midday, respectively, with a lag of 2-4 h between the two. The accumulated NRWIs increased with the development of the crusts across different cover types, however, there was no significant difference in maximum soil respiration rate observed at noon. Notably, the significant release of CO2 at midday was eliminated when the soil NRWIs were suppressed, demonstrating that the NRWIs were the primary determinant of the substantial CO2 release at midday. Furthermore, the soil sucrase activity, dehydrogenase activity, microbial richness, and the Chao1 index of soil microorganisms were significantly higher at noon than at night, indicating that microbial activity was greater during the day compared with at night. Our results confirm that the significant midday CO2 release in desert ecosystems is like a daily "micro-Birch effect" phenomenon induced by NRWIs. This phenomenon may be due to the transition between dormancy and activation of microorganisms mediated by NRWIs. This study demonstrates that NRWIs induce consistent daily pulses of CO2 in desert ecosystems, representing a previously overlooked microbial-driven pathway. Given the extensive coverage of deserts in global terrestrial ecosystems, this mechanism may have implications for carbon cycling and budget estimates in drylands and potentially at broader scales.

Phyllosphere microorganisms play a vital role in supporting host plant health and adaptability. Although previous research on the effects of host performance and their phylogenetic associations on phyllosphere microbial communities has predominantly focused on tropical, subtropical, and temperate forestry ecosystems, the responses of these microbial communities to plant phylogeny and functional traits in temperate desert environments remains poorly understood. In this study, we conducted a quantitative analysis of bacterial and fungal community structures in the phyllosphere of 39 plant species from the Gurbantunggut Desert, a typical temperate desert in Central Asia. Variation partitioning analysis revealed that plant phylogeny, leaf physicochemical properties, and leaf morphological characteristics collectively explained the variation in phyllosphere microbial communities. Specifically, these factors accounted for 19.26%, 14.53%, and 2.32% of the variance in bacterial communities, and 11.55%, 8.36%, and 2.19% of the variance in fungal communities, respectively. A significant hierarchical pattern emerged: plant phylogeny > leaf physicochemical properties > leaf morphological characteristics, highlighting the dominant role of plant filtering effects in community assembly. Linear mixed-effects model analysis further confirmed the significant influence of multiple plant attributes, including phylogeny and functional traits, on microbial community structure. Plant-microbe interaction analysis revealed distinct host preferences of microbial taxa across different plant taxonomic levels. Co-evolutionary analysis also indicated a significant phylogenetic association between host plants and their phyllosphere amplicon sequence variants (ASVs). Overall, our findings demonstrate that plant attributes, particularly plant phylogeny and functional traits, are key factors driving the assembly of phyllosphere microbial communities in deserts. This study provides new insights into species coexistence mechanisms in fragile habitats and enhances our understanding of plant-microbe interactions in global desert ecosystem.

Nitrogen-limited drylands are highly sensitive to environmental changes, with biological soil crusts playing a key role in biological nitrogen fixation. Ammonia oxidation, the rate-limiting step in nitrification, is essential for nitrogen retention in soils. Despite sustained high global nitrogen deposition, the impacts of varying nitrogen addition levels on nitrogen fixation, ammonia oxidation by crusts, and nitrogen cycling remain poorly understood. Crusts were sampled in April and October from plots in the Gurbantunggut Desert, where nitrogen had been applied for 13 years, to assess nitrogen fixation, ammonia oxidation rates, and the functional microbial community structure. Results indicated nitrogen addition reduced nitrogen fixation, with the highest nitrogen addition (3.0 g N m2 yr-1) causing a ∼60 % decline, suggesting a microbial shift towards reliance on added nitrogen. In contrast, low nitrogen addition (0.5 g N m-2 yr-1) enhanced ammonia oxidation by 293 %, likely due to the alleviation of substrate limitations. However, higher nitrogen addition (N1.5, N3.0) led to a reduction in ammonia oxidation, with microorganisms such as Scytonema, Nitrososphaera, and Nitrosopumilus playing key roles in both processes. Notably, nitrogen fixation rates were generally lower during the dry season, while ammonia oxidation increased under N0 treatment. Nitrogen addition influenced the nitrogen fixation and ammonia oxidation capacities of the crusts, heightening the risk of nitrogen loss but diminishing the influence of prolonged drought. These findings underscore the need to consider nitrogen levels and seasonal dynamics when managing soil nitrogen processes to maintain the stability of dryland ecosystems and the nitrogen cycle, it is essential to reduce anthropogenic nitrogen deposition and mitigate the growing impacts of drought.

Biological soil crusts (biocrusts) development is a fundamental factor affecting stability by wind prevention, sand fixation, and desert surface soil stability enhancement, and aridity is an important driver for altering soil stability in drylands. The physical properties of biocrusts and binding sand quantity (BSQ) are important indicators for characterizing the stability of desert soil. The relationships between biocrust physical properties and BSQ are not clear, which is not conducive to a comprehensive understanding of the ecological functions of biocrusts. The different successional stages of biocrusts in the arid region of Northwest China were selected to study their physical properties and BSQ. The physical properties and BSQ of the different types of biocrusts were measured. The responses of the physical properties and BSQ of different types of biocrusts to aridity were analyzed. The results showed that the physical properties and BSQ increased significantly with biocrust development. The thickness, roughness, compressive strength, shear strength, and BSQ of the biocrusts show a significant increasing trend with the development and increase of biocrusts and coverage. BSQ and compressive strength increased with increasing thickness and roughness. Physical properties, physical multifunctionality (P-SMF), and BSQ of different biocrust types showed significantly different trends with increasing aridity. The results of structural equation modeling also revealed that the P-SMF and BSQ had different responses with increasing aridity. This study contributes to a comprehensive understanding of biocrust structure and function, particularly for wind prevention and sand fixation, as well as surface stability. This study provides a new methodology and new ideas for determining the distribution and surface stability of biocrusts and is highly important for land management and conservation in drylands.

Biological soil crusts (BSCs) are essential components of drylands, yet the effects of their development on soil multifunctionality (SMF) and the drivers behind these effects remain unclear. We sampled 11 sites in Northwest China's deserts, representing different successional stages of BSC development (i.e. cyanobacterial, lichen and moss crusts) as well as bare sand areas. We assessed the SMF of the crust layer and underlying soil at various depths (0-2, 2-5, 5-10, 10-20 cm) and also explored the influence of climatic factors (mean annual temperature, aridity, and solar radiation), crust characteristics (compressive strength, roughness, and thickness), and soil properties (pH, electrical conductivity, soil water content) on SMF across these layers. The presence of BSCs significantly enhanced soil nutritional status [soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), ammonia (NH4+-N), nitrate (NO3--N), and available phosphorus (AP)] throughout the 0-20 cm soil depth and increased SMF in the top 0-10 cm. These positive effects intensified with as BSCs progressed from cyanobacterial to lichen to moss stages, but decreased with soil depth. In the crust layer, SMF across all BSC types was positively influenced by our climatic factors. However, as BSCs developed, the negative influence of climatic factors (mainly solar radiation) and soil properties (mainly pH) on SMF decreased, while the positive influence of crust characteristics (mainly thickness) increased. The influence of climate, crust, and soil factors on SMF also decreased with increasing soil depth and varied by BSC type. Further, our findings demonstrate that the BSC development can buffer the negative effects of increased soil pH and solar radiation on SMF while enhancing the positive effects of crust properties, particularly thickness. This highlights the importance of preserving and promoting BSC development to enhance surface soil multifunctionality and mitigate the adverse effects of climate change on dryland ecosystem multifunctionality.

Non-structural carbohydrates (NSC) are critical indicators of the carbon acquisition and consumption balance in vascular plants, and are equally important for biological soil crusts (BSCs), which serve as significant carbon sinks in arid regions. Nitrogen (N) deposition significantly alters NSC storage by affecting plant growth, photosynthesis, and the carbon-to-nitrogen ratio. However, the response of NSC to N deposition may vary across different developmental stages of BSCs due to differences in physiological structures and soil properties. We conducted a long-term field N addition experiment (2010-2021) in the Gurbantunggut Desert, with N rates from 0 to 3 g m-2 yr-1 and a 2:1 NH4+-N to NO3--N ratio, to examine the effects of N on NSC and their components (fructose, sucrose, soluble sugars, and starch) in three BSC types: cyanobacterial, lichen, and moss crusts. Our results revealed that the development of BSCs from cyanobacterial to lichen and moss crusts significantly alters NSC allocation, with an increasing ratio of soluble sugars to starch (0.24-1-1.68). As N added levels rise, NSC content in all three BSC types exhibits a nonlinear trend, characterized by low promotion and high inhibition, with distinct threshold points (N1.5-N0.5-N0.5). This phenomenon arises from shifts in the NSC driving factors under N addition: transitioning from soil nutrient dependence (cyanobacteria) to regulation by plant antioxidant enzyme activity (lichen), and ultimately to a more complex physiological regulation involving photosynthetic pigments and antioxidant enzyme activities (Moss). This study reveals the transition of BSCs from "environmental adapters" to "ecological regulators" throughout their successional stages. These findings provide new insights into the C metabolism of BSCs and have important implications for ecological restoration in N-impacted arid regions.

Aridity has serious impacts on the pools, fluxes and processes of terrestrial carbon (C) and nitrogen (N) cycles. Drylands, with high aridity, also being particularly sensitive to global shifts, require accurate estimation of soil organic carbon (SOC) and total nitrogen (STN) pools for a comprehensive grasp of dryland C and N dynamics within the global C and N cycle. Hence, SOC and STN of 2895 soil samples combined with 11 selected environmental covariates were collected from 175 sampling sites in the drylands of China, the spatial distributions of SOC density (SOCD) and STN density (STND) were mapped with best-performing random forest model. SOC0- 100cm and STN 0-100cm stocks were 30.84 and 2.02 Pg, respectively. Mean annual precipitation and soil moisture were identified as the primary drivers of SOCD 0-30cm and STND 0-30cm , while mean annual temperature influenced SOCD 30-50cm and STND 30-50cm , and soil clay content affected SOCD 50-100cm and STND 50-100cm . Future warming is projected to reduce both SOCD and STND, whereas increased precipitation is expected to have a positive effect on both variables in drylands. Under future climate scenarios outlined by the Representative Concentration Pathway, declines in both SOCD and STND are anticipated, with STND exhibiting a more pronounced decrease. A 1.5 degrees C increase in temperature had the greatest effect on SOCD, while a 15 % decrease in precipitation had the greatest effect on STND. In conclusion, the spatiotemporal estimations presented in this study serve as a valuable supplement to existing SOC and STN stock measurements, enhancing our understanding of C and N cycling in drylands. Our findings are instrumental for effective C and N sinks management, providing valuable data for informed decision-making. For example, afforestation in drylands can lead to significant increases in soil C and N stocks. However, In the future, further warming may lead to large losses of soil C and N in drylands.

The drying-rewetting of soil can increase the release of greenhouse gases over a short time period and is one of the key pathways for greenhouse gas emissions in many terrestrial ecosystems, particularly in drylands. The mechanisms underlying this pulse of greenhouse gas emissions remain nearly unknown. Here, we conducted simulated soil rewetting experiments using typical cover of dryland soils (bareland, cyanobacteria/lichen-covered soil, and moss-covered soil). The 13C, 15N, and 18O labeling techniques allowed to explore the intrinsic mechanisms of rapid carbon (C) and nitrogen (N) release from the soils following rewetting. We found that the hydroxyl radical (˙OH) was produced after soil rewetting via the rapid activation of microorganisms. The carbon dioxide (CO2) and nitrous oxide (N2O) production strongly decreased after ˙OH removal, whereas the methane (CH4) production was not affected. The synergistic action between ˙OH oxidation and microbial enzymatic reactions increased CO2 production. The ˙OH also stimulated the oxidation of NH4 + to NO3 - and dominated the N2O production. Our results confirm the role of ˙OH in the production of greenhouse gases and indicate that microbially mediated ˙OH oxidation mechanisms are an overlooked key pathway for the emission of greenhouse gases during the soil rewetting. In the context of climate change, the extreme weather-induced drying-rewetting cycles in soils are becoming more frequent, making greenhouse gas emissions via the ˙OH oxidation pathway increasingly important.

Background and aims Wild fruit forests are vital reservoirs of germplasm genetic and biodiversity. Unfortunately, wild fruit forests of Central Asia are in the decline due to fungal disease and insect pest outbreaks. A health soil microbial community may help ameliorate the degradation of wild trees by increasing their systematic resistance, stabilizing soil carbon pool, and maintaining the quality of the habitat environment. We evaluated soil bacterial and fungal community beneath the dominant tree species, Malus sieversii (Ledeb.) M. Roem, to identify potential interactions between wild fruit forest degradation events and soil microorganisms in the Tianshan Mountain, China. Methods Based on targeted metagenomics of the 16S rRNA and ITS (Internal Transcribed Spacer), we explored the bacterial and fungal microbial communities in soils beneath healthy and degraded M. sieversii trees (i.e., microbial biomass, species interactions, potential and niche breadth), and soil physicochemical properties. Results We found that the degradation of M. sieversii reduced the beta diversity of topsoil bacterial communities and fungal symbiotic groups. The decline in M. sieversii abundance loosened connections within bacterial and fungal co-occurrence networks. Community assembly identified higher migration rates in the topsoil around degraded M. sieversii for bacteria and for fungi, suggesting that dispersal restricted in degraded wild fruit forest soils. Ultimately, the demise of M. sieversii homogenized the soil bacteria resulting in a narrow niche-breadth, enhanced pathogenetic fungal species, and reduced beneficial symbiotic and saprotrophic fungal diversity. Conclusions Our results demonstrated that the degradation of M. sieversii leads to alterations in diversity, self-assembling and resource competitiveness of forest soil-dwelling microorganisms.

The distribution of biological soil crusts (BSCs) and shrubs in temperate deserts often forms a common landscape surface feature. As climate change continues, desert shrubs experience varying rates of mortality, which can have severe negative impacts on soil structure and function. However, it remains uncertain whether moss crusts, prevalent beneath shrub canopies, can mitigate the effects of shrub mortality on soil nutrient environments. Therefore, this study focuses on the Gurbantunggut Desert, a typical temperate desert in northern China, with a primary focus on the dominant shrubs, Ephedra przewalskii , and the advanced stage of moss crust development within BSCs. We collected soil samples from bare sand and moss crusts under living shrubs and dead shrubs and analyzed them for their carbon, nitrogen, phosphorus, and potassium contents. Additionally, we calculated soil nutrient multifunctionality, which measures a soil's ability to sustain multiple ecosystem services simultaneously, to provide a comprehensive assessment of the effects of shrub mortality on soil nutrient function. Our results indicate that shrub mortality led to reductions in soil moisture, pH, electrical conductivity, and levels of carbon, nitrogen, phosphorus, and potassium in exposed sand compared to the sand under living shrubs. However, the presence of moss crusts significantly alleviated the adverse effects of shrub mortality on soil carbon, nitrogen, phosphorus, and potassium levels. The nutrient multifunctionality index of the moss crust only decreased by 4%, while bare sand experienced a 67% reduction following shrub mortality. Standard error of the mean analysis results revealed that when shrubs and crusts coexisted, the impact of shrubs on soil nutrient multifunctionality was much stronger than that of the moss crust. Specifically, total nutrient content was the most influential factor driving changes in soil nutrient multifunctionality. In conclusion, in desert ecosystems with declining shrubs, moss crusts can mitigate the reduction in soil nutrient contents caused by shrub degradation, thereby maintaining soil stability and nutrient multifunctionality as a viable substitute.

Biological soil crusts (biocrusts) play pivotal ecological roles in regulating nitrogen cycling within desert ecosystems. While acknowledging the essential role played by ammonia-oxidizing microorganisms in nitrogen transformation, there remains a paucity of understanding concerning how disturbances to biocrusts impact the diversity and spatial distribution patterns among ammonia oxidizer communities within temperate deserts. This investigation delved into assessing how 4 years’ worth of removing biocrust influenced niche differentiation between nitrifying archaea and bacteria while also examining its effects on shaping community structures of predominant ammonia-oxidizing archaea (AOA) within the Gurbantunggut Desert soils. Despite notable variations in abundance of ammonia-oxidizing microbes across distinct soil depths throughout different seasons, it became apparent that removing biocrust significantly altered both the abundance and niche pattern for AOA alongside their bacterial counterparts during winter and summer periods. Notably dominating over their bacterial counterparts within desert soils, AOA displayed their highest archaeal to bacterial amoA gene copy ratio (6549-fold higher) at a soil depth of 5–10 cm during summer. Moreover, substantial impacts were observed upon AOA diversity along with compositional changes following such perturbation events. The aftermath saw an emergence of more diffuse yet dynamic AOA communities, especially noticeable amidst winter when nitrogen and water limitations were relatively alleviated. In summary, our findings underscore how interactions between biocrust coverages alongside factors like soil temperature, total carbon content, or NO3−_N concentrations govern niches occupied by ammoxidation communities whilst influencing assemblage processes too. The sensitivity shown by dominant AOAs towards biocrust removal further underscores how biocrust coverage influences nitrogen transformation processes while potentially involving other communities and functions in desert ecosystems.

Biological soil crusts (biocrusts) play a vital role in desert ecosystems. The sand-dune slope position crucially affects biocrust growth and development. This paper investigates the effect of slope position on nonstructural carbohydrates (NSCs) in biocrusts in the Gurbantunggut Desert. Samples were collected from the eastern and western slopes and the bottom of the slope. Biocrust coverage, soil physicochemical properties, and NSCs were assessed. The NSCs were more affected by the slope position in the lichen crusts than the algae crusts. The contents of NSCs and their components in the lichen crust were the highest at the bottom of the slope, while those of the algae crust were the highest at the eastern slope. In the algae crusts, soluble sugar, starch, and NSCs were positively correlated with the electrical conductivity, soil organic carbon, and ammonium nitrogen. In the lichen crusts, they were significantly positively correlated with the soil water content, electrical conductivity, total nitrogen, total phosphorus, and ammonium nitrogen. The structural equation model revealed that the most important factors affecting the NSCs were the changes in the soil nutrients caused for the algae crusts and the soil moisture and temperature for the lichen crusts. The slope position indirectly influenced the NSC variations in the biocrusts through the soil physicochemical properties, but the key factors affecting the NSC in the different types of biocrusts were different. In conclusion, biocrusts adapt to environmental discrepancies arising from slope position by modulating the NSC content and distribution pattern.

Biological soil crusts(BSCs)are the main active groundcover community in arid regions.BSCs can significantly affect the material cycle and energy exchange,improve the physical,chemical,and biological prop-erties of surface soil,and influence the soil multifunctionality(SMF).Moss crust is an important type of BSCs.This study investigates the SMF variability of moss crust-covered and bare sand in the deserts of northwestern ar-id regions,and explored the main drivers of the variability.We analyzed eight crucial ecosystem function indica-tors.SMF was calculated by applying the mean method and factor analysis approach.We used the ordinary least square and structural equation modeling to explore the drivers of SMF changes.The results show that:(1)soil monofunctionality and SMF under moss crust cover were higher than those in bare sand(P<0.05).(2)The drivers of the SMF change in bare sand and under moss crust cover were very different.The main drivers of SMF in bare sand were aridity and soil water content,whereas the driver of SMF under moss crust cover was soil sand content(Sand).(3)The mean annual temperature had the largest indirect effect on changes in SMF for both soil in bare sand and under moss crust cover.Therefore,the development of moss crust significantly increased SMF and,in addition,modulated the relevant drivers of SMF.Our results are important for a deep understanding of the differ-ences and drivers of SMF in desert soil with bare sand and under moss crust cover.

The continuous rise in global warming and dramatic changes in precipitation patterns have resulted in frequent extreme weather events, biodiversity loss, and ecosystem degradation. This has resulted in varying degrees of mortality in desert mosses, a ground cover type that maintains desert stability and provides important ecological functions. There is, however, a lack of research on the effects of moss mortality on soil multifunctionality (SMF) and microbial interactions in temperate deserts. This study compared and analyzed the soil nutrient content, enzyme activities, and the associated microbial community structure between living and dead moss crusts in the temperate Gurbantunggut Desert. The results indicated that moss mortality improved SMF by increasing the soil carbon content, nitrogen, phosphorus, and enzymatic activity. However, the mortality also considerably reduced the total biomass and abundance of bacteria and fungi in the topsoil, having no significant effect on their diversity. Additionally, a significant decrease in the connectivity and complexity of the soil bacterial and fungal networks was observed when compared to living moss crusts. This was especially noted in the fungal networks, where fungi were more sensitive than bacteria to moss mortality. Although the natural mortality of mosses increases SMF, there is also an increased risk of nutrient loss, thereby threatening ecosystem sustainability. It is, therefore, imperative to consider the causes of crustal degradation while developing management and restoration processes for degraded desert ecosystems.

Aims:(1)To study effects of mean annual precipitation(MAP)on the diversity and community assembly of bacterial communities in the Gurbantunggut Desert;(2)Further our understanding of how bacterial communities respond to desertification. Methods:We conducted the high-throughput sequencing data of bacterial communities from 30 soil samples(0-10 cm depth)collected from the Gurbantunggut Desert,where the MAP ranges from180 mm to 230 mm.We investigated the effect of MAP on the diversity of three defined categories of bacterial communities(whole,abundant and rare),and compared the compositions of the bacterial communities.Finally,we assessed the relative importance of deterministic and stochastic processes of the bacterial community assembly using the null model method. Results:The results showed that MAP had no significant influence on the richness and Shannon index of whole and abundant bacterial taxa(P＞0.05).However,the indices of richness and Shannon diversity of rare bacterial taxa were significantly decreased with MAP reduction(P＜0.05).Moreover,MAP had a noticeable effect on the community composition of the whole,abundant and rare bacterial communities,with the rare bacterial taxa having the highest levels of community variation and spatial turnover followed by whole and abundant bacterial communities,respectively.The results indicated that the whole,abundant,and rare bacterial taxa in the Gurbantunggut Desert responded differently to MAP.Rare bacterial taxa showed strong sensitivity to regional precipitation differences,whereas whole and abundant bacterial taxa were resistant to MAP variation.The null model analysis showed that dispersal limitation dominated the bacterial community assembly process in the Gurbantunggut Desert(＞73.0％).In contrast,the rare desert bacterial taxa were subject to heterogeneous selection(43.0％),indicating that the desert precipitation differences enhanced the environmental selection or species competition of the rare bacterial taxa.In addition,spatial distance and MAP determined the whole bacterial community construction,and the abundant and rare taxa respectively.Particularly,MAP played an essential role in balancing the relative importance between deterministic and stochastic processes of the rare bacterial taxa. Conclusion:Small-scale MAP differences in the Gurbantunggut Desert significantly alter the composition and assembly processes of the bacterial community.The community composition and turnover of rare bacterial taxa were affected strongly by MAP,which help mitigate the lag in the response of desert bacteria to environmental changes.Dispersal limitation isa stronger determinant of 0 diversity for whole and abundant bacterial taxa than for rare bacterial taxa,indicating that geographic distance explained more species turnover for desert whole and abundant bacterial taxa than for rare bacterial taxa,while the diversity distribution and ecological niche preference of desert rare bacteria were more precipitation-dependent than spatial geographic scale.