Arid Soils Research Articles

Pengaruh Jenis Tanah terhadap Semai Mahoni Daun Besar (Swietenia Macrophylla)

Big Leaf Mahogany (Swietenia macrophylla) is a tropical plant commonly found growing wild in teak forests and areas near the coast. This plant is also known for its resilience, meaning it can withstand harsh and arid soil conditions. Even without watering for months, mahogany can still survive. The propagation of this plant can be done through seeds, as well as through air layering or grafting. When used for medicinal purposes, it should not be treated with chemical (inorganic) fertilizers or pesticides. The significance of this research lies in providing valuable information to relevant institutions about the suitable soil type for propagating Big Leaf Mahogany (Swietenia macrophylla) seedlings, ensuring high-quality seedlings for reforestation or afforestation efforts. The research was conducted at the Greenhouse of the Faculty of Agriculture from March to June 2023. The objective of this study was to determine the effect of different soil types on the growth of Big Leaf Mahogany (Swietenia macrophylla) seedlings. The experimental design used in this research was a Completely Randomized Design (CRD) with 2 (two) treatments and 3 (three) replications. The treatments consisted of: A (Regosol soil) and A2 (Podsolik soil). The research results indicate that Regosol soil type provided better average growth results for Big Leaf Mahogany (Swietenia macrophylla) seedlings.

Distinct composition patterns of bacterial and fungal communities and biogeochemical cycling genes depend on the vegetation type in arid soil

Semi-arid and arid regions account for >40 % of the land area worldwide and provide food resources for the world. Nutrient management by farmer's practices, such as fertilization, improves crop production in semi-arid and arid regions, but this can also affect the composition and function of the soil microbial communities. Therefore, in this research, we have examined the composition of the microbial community and biogeochemical cycling genes in arid soil, subjected to nutrient management by farmer's practices, using high-throughput sequencing and a quantitative-PCR-based chip, Quantitative microbial element cycling (QMEC). Proteobacteria and Acidobacteriota, and Ascomycota dominated the composition of bacterial and fungal communities, respectively. Scrubland soils without nutrient management possessed the lowest Chao1 richness and Shannon diversity of the bacterial community but showed higher average Shannon diversity of the fungal community. Acidobacteriota and Gemmatimonadota, copiotrophic members, were found to have a higher percentage in nutrient-managed soils (cotton, fruit, and vegetables) than the scrubland soils. However, Actinobacteria, autochthonous bacteria, were found to have higher relative abundance in soils from the scrubland than from cotton, fruits, and vegetables. Besides, scrubland soils had a higher relative abundance of Glomeromycota (arbuscular mycorrhizal fungi) to support plant growth in the arid and oligotrophic soils. Vegetable soil microbial communities exhibited a higher potential for biogeochemical cycling than soils used for other vegetation types. In soils from cotton and fruits, the bacterial community was more sensitive to soil properties than the fungal community. Nutrients strongly affected the composition of bacterial and fungal communities in soils from vegetables, while salinity drove the microbial communities in scrubland soils. Our results suggest that vegetation types determined the distinct biodiversity patterns of the microbiota (bacteria and fungi) and associated biogeochemical cycling genes in arid soils.

Distribution and Driving Mechanisms of Antibiotic Resistance Genes in Desert-Oasis Continuum

The oasis agro-ecosystem is a complex ecosystem with intensive human activities in arid areas. Microbial antibiotic resistance is posing threats to human health and ecological balance. It is of great importance to investigate the diversity, distribution profiles, and driving factors of soil antibiotic resistance genes under different land use patterns in a desert-oasis continuum, especially for assessing soil environmental and human health risks in arid regions. In this study, high throughput sequencing combined with high throughput quantitative PCR were used to investigate the microbial community structure and patterns of antibiotic resistance genes in a desert-oasis continuum, aiming to explore the distribution characteristics and driving mechanisms of soil resistance genes. The results showed that the diversity and abundance of antibiotic resistance increased significantly from the edge of desert to the central oasis, along with Dest, Cotn, Maiz, Reed, and Sedt, consecutively, implying that farmland soil was an important reservoir of resistance genes, which was closely related to land use and land cover change. Soil microbial communities were significantly correlated with antibiotic resistance genes. Thiobacillus, Pontibacter, Nocardioides, Salinimicrobium, Solirubrobacter, and Streptomyces were important potential hosts of various resistance genes. The patterns of antibiotic resistance genes were shaped by heavy metal elements, MGEs, and microbial communities in arid soil, which accumulatively accounted for 70% of the variations in resistance genes alone or together and therefore drove the occurrence, enrichment, and evolution of resistance genes in agricultural soil of the desert-oasis continuum.

Soil moisture estimation from Sentinel-1 interferometric observations over arid regions

We present an experimental methodology based on interferometric synthetic aperture radar (InSAR) time series analysis that can provide surface (top 5 cm) soil moisture (SSM) estimations over sandy arid soils. A co-registered Single Look Complex (SLC) SAR stack as well as meteorological information are required as input of the proposed methodological workflow. The proposed methodology consists of five steps. In the first step, meteorological data are exploited to identify the snow/ice free SAR acquisition related to lowest SSM level. In the second step, interferometric (coherence and phase closure) observables over a spatial grid are calculated. In the third step, for each grid cell the ordering of SAR acquisitions according to the SSM is performed. The sorting is performed by starting from the SAR acquisition related to lowest SSM level and by exploiting coherence and backscattering information. In the fourth step, for each grid cell the coherence values due to SSM variations are calculated by exploiting the ordering of SAR acquisitions according to the SSM. In the fifth step, SSM is estimated by inverting an analytical interferometric model using coherence values due to SSM variations and phase closure information. The proposed method estimates SSM over arid regions by ordering SAR acquisitions based on SSM, by calculating coherence values due to SSM variations and by inverting an interferometric model.A case study over an arid region in California/Arizona is presented. The proposed workflow was applied in Sentinel-1 (C-band) VV-polarized InSAR observations. The estimated SSM results were assessed with independent SSM observations from a station of the International Soil Moisture Network (ISMN) (RMSE: 0.029 m3/m3 R: 0.78) and with ERA5-Land reanalysis model data (RMSE: 0.049 m3/m3 R: 0.62). In summary, the proposed methodology was able to provide accurate SSM estimations at high spatial resolution (∼250 m). A discussion of the benefits and the limitations of the proposed methodology highlighted the potential of interferometric observables for SSM estimation over arid regions.

Arginine and methionine increase the enzymatic activity of microbes involved in N and P cycles in arid soil from the Chihuahuan desert

Root exudates are mainly composed of sugars, organic acids, and amino acids. These are carbon sources that recruit beneficial bacterial communities in the rhizosphere. However, the composition of the root exudates is variable and mainly unknown for plants from arid lands, such as Agave lechuguilla Torr. This work studied the effect of different metabolites identified in the rhizosphere of A. lechuguilla Torr. (Maltose, lactose, oxalic and tartaric acids, arginine, and methionine), over the enzymatic activity and abundance of nitrogen-fixing bacteria and organic phosphorus mineralizing bacteria, as well as the changes in the nutrient availability in the soil. It was found that only the amino acids increased the nitrogenase and phosphatase activity, and these increments were reflected in the available nutrient concentration in the soil. Likewise, the presence of carbon and nitrogen from the amino acids may reduce the C:N ratio in the soil, enhancing the mineralization of organic matter and the concentration of ammonia, nitrite, and nitrates. This work shows the complexity of the nutrient recycling process in the soil and the essential role of bacteria in making nutrients available to plants. Understanding this process could aid in improving the establishment of plants in eroded ecosystems or under the harsh conditions of arid environments.

Indigenously produced biochar retains fertility in sandy soil through unique microbial diversity sustenance: a step toward the circular economy.

Agricultural productivity in the arid hot desert climate of UAE is limited by the unavailability of water, high temperature, and salt stresses. Growing enough food under abiotic stresses and decreasing reliance on imports in an era of global warming are a challenge. Biochar with high water and nutrient retention capacity and acid neutralization activity is an attractive soil conditioner. This study investigates the microbial community in the arid soil of Dubai under shade house conditions irrigated with saline water and the shift in the microbial community, following 1 year of amendment with indigenously prepared biochar from date palm waste. Amplicon sequencing was used to elucidate changes in bacterial, archaeal, and fungal community structures in response to long-term biochar amendment. Samples were collected from quinoa fields receiving standard NPK doses and from fields receiving 20 and 30 tons ha-1 of biochar, in addition to NPK for 1 year. Water holding capacity, pH, electrical conductivity, calcium, magnesium, chloride, potassium, sodium, phosphorus, total carbon, organic matter, and total nitrogen in the soil from biochar-treated and untreated controls were determined. The results show that soil amendment with biochar helps retain archaeal and bacterial diversity. Analysis of differentially abundant bacterial and fungal genera indicates enrichment of plant growth-promoting microorganisms. Interestingly, many of the abundant genera are known to tolerate salt stress, and some observed genera were of marine origin. Biochar application improved the mineral status and organic matter content of the soil. Various physicochemical properties of soil receiving 30 tons ha-1 of biochar improved significantly over the control soil. This study strongly suggests that biochar helps retain soil fertility through the enrichment of plant growth-promoting microorganisms.

Comparison of the Fuzzy Analytic Hierarchy Process (F-AHP) and Fuzzy Logic for Flood Exposure Risk Assessment in Arid Regions

Flood risk assessment is an important tool for urban planning, land development, and hydrological analysis. The flood risks are very high in arid countries due to the nature of the rainfall resulting from thunderstorms and the land cover, which comprises mostly very dry arid soil. Several methods have been used to assess the flood risk, depending on various factors that affect the likelihood of occurrence. However, the selection of these factors and the weight assigned to them remain rather arbitrary. This study assesses the risk of flood occurrence in arid regions based on land cover, soil type, precipitation, elevation, and flow accumulation. Thematic maps of the aforementioned factors for the study area were prepared using GIS. The Fuzzy Analytic Hierarchy Process (F-AHP) was used to calculate the likelihood of the flood occurrence, and land use was used to assess the exposure impact. Using the likelihood map (i.e., probability) from the Fuzzy-AHP and an exposure map, the flood risk was assessed. This method was applied to Qatar as a case study. Results were compared with those produced by fuzzy logic. To explore the pairwise importance of the F-AHP, equal weight analysis was performed. The resulting risk map shows that the majority of urbanized areas in Qatar are within the high-risk zone, with some smaller parts within the very high flood-risk area. The majority of the country is within the low-risk zone. Some areas, especially land depressions, are located within the intermediate-risk category. Comparison of Fuzzy logic and the F-AHP showed that both have similarities in the low-risk and differences in the high-risk zones. This reveals that the F-AHP is probably more accurate than other methods as it accounts for higher variability.

Effectiveness of Biochar, Organic Matter and Mycorrhiza to Improve Soil Hydrophysical Properties and Water Relations of Soybean under Arid Soil Conditions

Effectiveness of Biochar, Organic Matter and Mycorrhiza to Improve Soil Hydrophysical Properties and Water Relations of Soybean under Arid Soil Conditions

Genetic diversity, symbiotic efficiency, stress tolerance, and plant growth promotion traits of rhizobia nodulating Vachellia tortilis subsp. raddiana growing in dryland soils in southern Morocco

In the present study, we analyzed the genetic diversity, phylogenetic relationships, stress tolerance, phytobeneficial traits, and symbiotic characteristics of rhizobial strains isolated from root nodules of Vachellia tortilis subsp. raddiana grown in soils collected in the extreme Southwest of the Anti-Atlas Mountains in Morocco. Subsequent to Rep-PCR fingerprinting, 16S rDNA gene sequencing of 15 representative strains showed that all of them belong to the genus Ensifer. Phylogenetic analysis and concatenation of the housekeeping genes gyrB, rpoB, recA, and dnaK revealed that the entire collection (except strain LMR678) shared 99.08 % to 99.92% similarity with Ensifer sp. USDA 257 and 96.92% to 98.79% with Sinorhizobium BJ1. Phylogenetic analysis of nodC and nodA sequences showed that all strains but one (LMR678) formed a phylogenetic group with the type strain “E. aridi” LMR001T (similarity over 98%). Moreover, it was relevant that most strains belong to the symbiovar vachelliae. In vitro tests revealed that five strains produced IAA, four solubilized inorganic phosphate, and one produced siderophores. All strains showed tolerance to NaCl concentrations ranging from 2 to 12% and grew at up to 10% of PEG6000. A greenhouse plant inoculation test conducted during five months demonstrated that most rhizobial strains were infective and efficient. Strains LMR688, LMR692, and LMR687 exhibited high relative symbiotic efficiency values (respectively 231.6 %, 171.96 %, and 140.84 %). These strains could be considered as the most suitable candidates for inoculation of V. t. subsp. raddiana, to be used as a pioneer plant for restoring arid soils threatened with desertification.

Jack Dwayne Farmer April 18, 1947-February 22, 2023.

Jack Dwayne Farmer April 18, 1947-February 22, 2023.

Diversity of Bacteria Cultured from Arid Soils and Sedimentary Rocks under Conditions of Available Water Deficiency

Diversity of Bacteria Cultured from Arid Soils and Sedimentary Rocks under Conditions of Available Water Deficiency

Diversity of Bacteria Cultured from Arid Soils and Sedimentary Rocks under Conditions of Available Water Deficiency

The diversity of bacteria cultured from the soil of the Negev desert (Israel, sample SN2) and the sedimentary rock of the Sahara Desert (Tunisia, sample Alg) has been studied. To assess the ability of bacteria to metabolize at different levels of moisture availability and to reveal bacterial diversity more fully, culturing was carried out on R2A medium with the addition of glycerol to establish a certain level of water activity (Aw) in range from 1.0 to 0.9 (with a step of 0.01 Aw). After incubation, unique morphotypes of cultured bacteria were isolated, described, identified by 16S rRNA sequencing, and tested for the ability to grow in the Aw gradient in pure cultures. After incubation and isolation, 355 strains were identified and tested. Culturable bacteria were found at Aw 0.95 and higher. With a decrease in Aw from 1 to 0.95, the number of cultured bacteria decreased from 105 and 107 CFU/g in samples SN2 and Alg, respectively, to 2 × 104 CFU/g in both studied samples. As a result of culturing, representatives of 34 genera of bacteria were isolated, mainly representatives of the phylum Actinobacteria; representatives of the genera Arthrobacter, Kocuria, and Pseudarthrobacter dominated. At this, 38 strains with low similarity of nucleotide sequences with databases and, probably, being representatives of previously undescribed species of the genera Agrococcus, Arthrobacter, Bacillus, Brachybacterium, Cellulomonas, Conyzicola, Kocuria, Microbacterium, Okibacterium, Rathayibacter, and Sphingomonas were revealed. Testing the strains for their ability to grow in pure culture in a gradient of Aw values revealed 18 strains of the genera Arthrobacter, Kocuria, Brachybacterium, Serratia, and Leucobacter capable of growing at Aw 0.91. The study confirms the data that desert soils and rocks are a depository of previously undescribed bacterial species and can also be a valuable source of biotechnologically promising strains.

Remediation of arsenic-contaminated calcareous agricultural soils by iron-oxidizing bacteria combined with organic fertilizer.

In arid soil with low-iron and high-calcium carbonate contents, the fate of arsenic (As) is mainly controlled by the contents of calcium and organic matter in the soil. However, there is still a lack of knowledge about their interaction and that effect on their absorption by maize. The purpose of this study was to explore the long-term immobilization and repair mechanism of in situ As-contaminated farmland. We designed three treatments: iron-oxidizing bacteria (FeOB), organic fertilizer, FeOB and organic fertilizer added in combination. After 140-day field farmland remediation trial, the results showed that the FeOB can effectively immobilize the water-soluble As (FS1) in soil, and the organic fertilizer promoted the remediation of FeOB. In addition, the content of As in maize grains was reduced after treatment by FeOB and organic fertilizer. The XRD and XPS analysis of the topsoil showed that the combined treatment of FeOB and organic fertilizer promoted the formation of calcium arsenate mineral with low solubility and high stability; As(III) would gradually transform into As(V). The biological iron (hydr)oxide can increase the contents of Fe and As in the rhizosphere and form iron plaques on the surface of the roots by SEM-EDS analysis of maize root. Collectively, these results clarify the main biogeochemical ways to control the fate of As in calcareous soils with low-iron and low-organic matter contents and provide a basis for in situ remediation of As.

Soil moisture content-based analysis of terrestrial ecosystems in China: Water use efficiency of vegetation systems

Water is a prerequisite for the formation of earth-biochemical-ecological systems. Differences in the spatial and temporal distribution of water resources are important factors in the formation of differences in the distribution of vegetation in terrestrial ecosystems and are key to the differences in vegetation productivity. Vegetation water use efficiency is calculated by the total amount of fixed biogenic carbon per unit mass of water consumed in photosynthesis and can be used to assess the intensity and capacity of an ecosystem to use water biomass. Based on remote satellite sensing data, this study proposes a new water use efficiency assessment model. The model was validated using flux site data, and we analyzed the relative contribution of climate factors to soil moisture use efficiency using a first-difference method. The results revealed the following: (1) The soil moisture use efficiencies (SUE) of remote sensing data inversions that were evaluated using flux site data based on correlation coefficients and Nash coefficients showed high reliability, and only the NMG (Inner Mongolia) station showed low correlation among the nine sites. (2) Among the nine agricultural sub-regions in China, only the SUE of the Qinghai-Tibet Plateau region showed a decreasing trend (−1.08 g C/m−2 kg H2O yr), while all other regions showed an increasing trend. (3) The highest vegetation soil moisture use efficiency (1.83 g C/m−2 kg H2O) was found in ferralisols, while the lowest vegetation SUE (0.17 g C/m−2 kg H2O) was found in arid soils. The SUE of different vegetation types showed the characteristics of forest > scrub > cultivated vegetation > wetland > grassland. (4) The relative contribution of gross primary productivity (GPP) to the change in SUE was 37.53%, while the relative contribution of soil moisture content to the change in SUE was −26.71%. Among the five climatic factors, temperature was the most dominant factor affecting the change in SUE, followed by precipitation, net radiation, leaf area index, and potential evapotranspiration. Revealing the relationship between terrestrial ecosystem GPP, soil moisture content, and their responses to climate factors is a prerequisite for understanding the adaptation strategies of regional terrestrial ecosystems to global climate change, which can help to inform decision-making for the sustainable development of ecosystems.

Valorization of Waste from Argan Seeds for Polyhydroxybutyrate Production Using Bacterial Strains Isolated from Argan Soils.

The aim of this work was to study the valorization of argan seed pulp, a waste material obtained from argan oil extraction, for the biosynthesis of polyhydroxybutyrate (PHB). A new species that showed the metabolic capacity for the conversion of argan waste into the bio-based polymer was isolated from an argan crop located in Teroudant, a southwestern region of Morocco, where the arid soil is exploited for goat grazing. The PHB accumulation efficiency of this new species was compared to the previously identified species 1B belonging to the genus Sphingomonas, and results were reported as dry cell weight residual biomass and PHB final yield measured. Temperature, incubation time, pH, NaCl concentration, nitrogen sources, residue concentrations, and culture medium volumes were analyzed with the aim of obtaining a maximum accumulation of PHB. UV-visible spectrophotometry and FTIR analysis confirmed that PHB was present in the material extracted from the bacterial culture. The results of this wide investigation indicated that the new isolated species 2D1 had a higher efficiency in PHB production compared to the previously identified strain 1B, which was isolated from a contaminated argan soil in Teroudant. PHB final yield of the two bacterial species, i.e., the new isolated and 1B, cultivated under optimal culture conditions, in 500 mL MSM enriched with 3% argan waste, were 21.40% (5.91 ± 0.16 g/L) and 8.16% (1.92 ± 0.23 g/L), respectively. For the new isolated strain, the result of the UV-visible spectrum indicates the absorbance at 248 nm, while the FTIR spectrum showed peaks at 1726 cm-1 and 1270 cm-1: these characteristic peaks indicated the presence of PHB in the extract. The data from the species 1B UV-visible and FTIR spectra were previously reported and were used in this study for a correlation analysis. Furthermore, additional peaks, uncharacteristic of standard PHB, suggest the presence of impurities (e.g., cell debris, solvent residues, biomass residues) that persisted after extraction. Therefore, a further enhancement of the sample purification during extraction is recommended for more accuracy in the chemical characterization. If 470,000 tons of argan fruit waste can be produced annually, and 3% of waste is consumed in 500 mL culture by 2D1 to produce 5.91 g/L (21.40%) of the bio-based polymer PHB, it can be estimated that the amount of putative PHB that can be extracted annually from the total argan fruit waste is about 2300 tons.

Dual use of solar power plants as biocrust nurseries for large-scale arid soil restoration

Dual use of solar power plants as biocrust nurseries for large-scale arid soil restoration

Using solar farms as a platform for the ecological restoration of arid soils

Using solar farms as a platform for the ecological restoration of arid soils

Geochemical evidence of fluoride behavior in loess and its influence on seepage characteristics: An experimental study

High background levels of fluorine in groundwater and soil in arid and semi-arid loess regions pose a severe threat to socio-economic development and human health, necessitating the evaluation of fluorine migration in loess. In this study, static leaching and dynamic seepage tests as well as scanning electron microscopy, mercury intrusion porosimetry, and X-ray fluorescence analyses were conducted using loess as the porous medium. Additionally, simulations using PHREEQC software were performed. The results indicated that the studied loess had a high background level of fluorine. Geochemical processes closely related to fluorine include dissolution of gypsum and dolomite, precipitation/dissolution of calcite and fluorite, and ion exchange between CaX and NaX. Under seepage of water with high fluorine levels, soil particles flocculated and formed aggregates; furthermore, the contact area between soil particles reduced, resulting in point-to-point contact between particles. Consequently, pores changed from small (intra- and inter-particle pores) to large (intra- and inter-granular pores) scale pores. Permeability initially decreased rapidly, then remained relatively stable, and subsequently rapidly increased with the passage of time. This was attributed to the dissolution of calcium minerals in loess, yielding Ca2+, which induced the precipitation of fluorite and promoted the dissolution of carbonates. Cation exchange and dissolution of other components were also important factors influencing permeability. The findings of this study can elucidate the coupling between loess microstructure, seepage behavior, and geochemical actions under the influence of high‑fluorine water, and are of great significance for in-situ regional research in loess areas.

Multispectral Remote Sensing Monitoring of Soil Particle-Size Distribution in Arid and Semi-Arid Mining Areas in the Middle and Upper Reaches of the Yellow River Basin: A Case Study of Wuhai City, Inner Mongolia Autonomous Region

Particle size distribution is an important characteristic of reclaimed soil in arid and semi-arid mining areas in western China, which is important in the ecological environment protection and control of the Yellow River Basin. Large-scale coal resource mining disturbances have caused serious damage to the fragile ecological environment. The timely and accurate dynamic monitoring of mining area topsoil information has practical significance for ecological restoration and management evaluation. Investigating Wuhai City in the Inner Mongolia Autonomous Region of China, this study uses Landsat8 OLI multispectral images and measured soil sample particle size data to analyze soil spectral characteristics and establish a particle size content prediction model to retrieve the particle size distribution in the study area. The experimental results and analysis demonstrate that: (1) the 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum Vector version) atmospheric correction model is more accurate than the FLAASH (Fast Line-of-sight Atmospheric Analysis of Hypercubes) model in arid and semi-arid areas with undulating terrain; (2) 0–40 cm is the optimum soil thickness for modeling and predicting particle size content in this study; and (3) the multi-band prediction model is more precise than the single-band prediction model. The multi-band model’s sequence of advantages and disadvantages is SVM (Support Vector Machine) > MLR (Multiple Linear Regression) > PLSR (Partial Least Squares Regression). Among them, the 6SV-SVM model has the highest precision, and the prediction precision R2 of the 3 particle sizes’ contents is above 0.95, which can effectively predict the soil particle-size distribution and provide effective data to support topsoil quality change monitoring in the mine land reclamation area.

Structural Characteristics and Assembly Mechanisms of Soil Microbial Communities under Water-Salt Gradients in Arid Regions.

Exploring the structural characteristics of arid soil microbial communities and their assembly mechanisms is important for understanding the ecological characteristics of arid zone soils and promoting ecological restoration. In this study, we used Illumina high-throughput sequencing technology to study soils in the arid zone of the Lake Ebinur basin, determined the differences among soil microbial community structures in the study area under different water-salt gradients, and investigated the effects of environmental factors on microbial community structure and assembly mechanisms. The results show the following: the microbial community alpha diversity exhibited a significantly higher low water-salt gradient (L) than high water-salt gradient (H) and medium water-salt gradient (M). The pH was most strongly correlated with soil microbial community structure, where the alpha diversity indices of the bacterial community and fungal community were significantly negatively correlated with pH, and the Bray-Curtis distance of bacterial community was significantly positively correlated with pH (p < 0.05). The complexity of bacterial community co-occurrence networks showed a significantly higher L than H and M, and the complexity of fungal community co-occurrence network showed a significantly lower L than H and M. The cooperative relationship of H and M in the co-occurrence networks was stronger than that of the L, and the key species of the microbial co-occurrence network were different under different water-salt gradients. Stochastic processes dominated the assembly mechanism of the microbial community structure of soil, and the explanation rates of deterministic and stochastic processes were different under different water-salt gradients, with the highest explanation rate of stochastic processes on the L accounting for more than 90%. In summary, the soil microbial community structure and assembly mechanisms significantly differed across water-salt gradients, and these findings can help provide a reference for further research on soil microbiology in arid zones.