In this study, activated carbons (ACs) were produced through a one-step physical activation of raw biomasses (distilled mint, chestnut wood, chestnut leaves) in pure CO2 atmosphere. The biomasses were activated without any pretreatment. The textural properties of the ACs were characterized with N2 and CO2 adsorption measurements, and advanced models such as Dubinin-Astakhov (DA) equation and 2D-NLDFT model were applied to provide a comprehensive understanding of the porosity development of the ACs. Highly microporous ACs were successfully produced from distilled mint through one-step activation (up to 937 m²/g). The evolution of the specific surface area as a function of activation degree of the resource follows a bell-shaped curve, with an optimum that depends on the nature of the resource. Regarding the pore size distribution, both the DA and 2D-NLDFT models agree that micropore heterogeneity increases as activation progresses. Finally, this study highlights the challenges associated with applying advanced adsorption-based textural characterization methods to ash-rich, heterogeneous biomass-derived chars. A discrepancy was observed between the CO2 adsorption data and the 2D-NLDFT and DA models for highly activated chars. These deviations indicate that adsorption behavior is likely governed by multiple interrelated factors, potentially arising from the presence of heterogeneous inorganic fractions, including carbon structure evolution, pore architecture, and surface chemistry, thereby complicating the interpretation of CO2-sorption-derived textural parameters.

The oxalate-carbonate pathway (OCP) is a metabolic process that converts atmospheric carbon dioxide into biogenic carbonates, representing a potential long-term sink of carbon in the form of inorganic carbon in soils, particularly in drylands. This pathway involves oxalates, organic crystals ubiquitous across the plant kingdom. To date, quantifying soil oxalates in low carbon content soils remained challenging owing to the absence of suitable methods: existing approaches require extensive sample pretreatment, have prohibitively high quantification limits, and have not been adapted for soil matrices. This study presents a novel approach for oxalate quantification in low carbon soils using Rock-Eval® thermal analysis, which simultaneously characterises and quantifies soil organic and inorganic carbon. Bare Arenosol samples from a hyperarid ecosystem (Sharaan National Park, Saudi Arabia) were amended with pure oxalate across a gradient from 0 to 7.14 mg g-1. Thermal analysis revealed a distinctive four-peak signature associated with oxalate content. However, the thermal decomposition of oxalate into carbonate hinders direct oxalate quantification and their differentiation from background soil carbonates. We address this by developing oxalate and carbonates quantification formulas based on the CO emitted during pyrolysis between 400 and 550 °C as a reliable linear proxy for oxalate content. Validation through application to Arenosols samples from Sharaan yields results consistent with active OCP expression. These findings advance our understanding of the role of oxalates and the OCP in the carbon cycle, particularly for assessing the carbon sequestration capacity of hyperarid ecosystems and monitoring ecological restoration in such ecosystems.

Secondary metabolites play crucial roles in cellular processes and physiological activities and act as key components of the plant defense system. Moreover, these compounds offer a multitude of benefits to humans thanks to their biological activities, rendering them increasingly significant in the food and pharmaceutical industries. The plant species, genotype, physiology, developmental stage, and environmental factors during the plant life cycle determine the type and concentration of bioactive molecules produced. Among environmental influences, abiotic stresses, particularly drought and salinity, strongly influence secondary metabolites biosynthesis. Desert plants are of particular interest in this context, as their continuous exposure to extreme water limitation and high salinity has driven adaptive mechanisms that enhance stress-responsive secondary metabolite production. Recent research has highlighted the close interplay between stress signaling and defense response in regulating secondary metabolite biosynthesis. Plants manifest various morphological, physiological, and phytochemical responses to drought and salinity, and the mechanisms underlying these responses are examined in this literature review paper. Additionally, we analyzed how biotechnological approaches enhance understanding of the signaling pathways involved in secondary metabolites production. These processes occur at subcellular, cellular, organ, and whole plant levels during both in vivo and in vitro growth. Particular focus has been placed on applications of metabolic engineering of biosynthetic pathways and their intermediates.

Lavandula coronopifolia Poir. is a medicinal evergreen shrub, wildly distributed in rocky and arid environments. It belongs to the Lamiaceae family, known by the large array of bioactive compounds it contains. Drought and salinity present major threats in arid zones and severely penalize the potential yield of naturally growing desertic plants; however, it may affect the synthesis and accumulation of their metabolites. Few studies have investigated the response of Lavandula species to abiotic stresses and to the best of our knowledge, none have been conducted on L. coronopifolia. Our study aims to investigate various responses of this species to water deficit and salt stress under controlled conditions. Two distinct experiments were conducted in a growth chamber, each lasting one month. The first one focused on water stress, with plants subjected to four water treatments: control (100% field capacity (FC)), moderate water deficit (50% FC), severe water stress (25% FC), and very severe water stress (alternating irrigation to 50% FC for one week followed by cessation of watering for the next week). These treatments were arranged in a randomized complete block design (RCBD) with 3 blocks, each containing 3 replicates per treatment, resulting in 9 replications per treatment. The second experiment investigated the effect of salt stress, where plants were exposed to four NaCl concentrations: 0, 5, 10, and 20 dS/m. This experiment was also conducted using an RCBD, with 4 blocks and 4 replicates per treatment within each block, giving a total of 16 repetitions per treatment. Growth parameters, oxidative stress indicators as well as secondary metabolite content were determined. Results have shown that under both water and salt stress conditions, plant fresh and dry weights decreased significantly. Malondialdehyde levels increased under intense stress in both experiments, indicating enhanced lipid peroxidation. Protein content increased under water stress but showed no change under salt stress. Phenolic and flavonoid contents increased with water stress but decreased with salt stress. Antioxidant activity remained stable under water stress and showed a significant increase with salt stress. These findings enhance our understanding of how plants modulate various traits in response to distinct water and salt stress conditions.

Haloxylon salicornicum is a desert plant well-adapted to extreme arid environments. This study explores how this species adjusts its metabolism in response to diurnal and seasonal environmental changes. Herein, we examined its metabolic responses across two soil types (clay and sandy), two seasons (winter and summer), and two timings (dawn and midday), focusing on water status and primary metabolites’ profiling via untargeted metabolomics.The variation in soil properties at 1 m depth did not significantly affect the metabolic responses of H. salicornicum plants, while notable changes occurred across seasons and timings. During winter, the plants’ water status was relatively higher (water potential − 1 MPa), facilitating the activation of anabolic pathways, specifically carbon fixation and the biosynthesis of carbohydrates and amino acids, thereby allowing growth and accumulation of reserves. In summer, however, water potential decreased sharply ( − 5 MPa), leading to the stimulation of catabolic processes, particularly starch breakdown, to sustain carbon metabolism and maintain energy production. Additionally, the plants accumulated antioxidants like ascorbate, glutathione, and caffeic acid to combat oxidative stress caused by heat and drought. Overall, H. salicornicum exhibited remarkable metabolic flexibility, especially through nocturnal activity, to survive harsh desert conditions. These findings contribute to understanding the mechanisms by which desert plants endure extreme stress and lay the groundwork for future genetic studies.

In hyperarid ecosystems, vegetation often forms patchy so-called fertile islands, structured by perennial pillar plants that strongly influence soil carbon dynamics and ecosystem functioning. This study quantified their effects on soil organic carbon (SOC), soil inorganic carbon (SIC), and SOC quality in two areas of Sharaan National Park, with area 1 corresponding to canyon-protected arid woodland systems and area 2 to open dune-dominated environments, using the Rock-Eval (R) Oxypure method, a rapid thermal oxidative technique enabling simultaneous characterization of organic and inorganic carbon fractions. SOC stocks ranged from 2.6 to 72.5 Mg C ha(-1), with mean values of 4.3 +/- 2.6 to 32 +/- 14 Mg C ha(-1) in area 1 and 4.3 +/- 2.6 to 51.1 +/- 19.4 Mg C ha(-1) in area 2. In contrast, SIC stocks remained low, averaging 6.9 +/- 4.1 Mg C ha(-1) and 6.3 +/- 3.1 Mg C ha(-1) in areas 1 and 2, respectively. In area 1, the nitrogen-fixing species Retama raetam and Vachellia gerrardii were associated with higher SOC contents, whereas in area 2, Haloxylon persicum structured SOC distribution throughout the soil profile. SOC stocks were primarily controlled by soil depth and stable carbon pools in area 1, and by exchangeable cations (CaO, MgO) in area 2. The studied soils were characterized by a predominance of labile SOC pools, with relatively large labile SOC fractions observed at all soil depths. The results showed that the influence of pillar plants on SOC pool sizes was minor compared to control soils. SOC dynamics in hyper-arid environments are governed by the interaction between limited organic inputs, severe abiotic constraints (low moisture, high temperatures, sandy texture), and localized biotic hotspots (e.g., plant colonies and nitrogenfixing species). Our findings further demonstrate that certain plant species play a crucial role in enhancing deep-soil carbon stabilization mechanisms, which are essential for the development of sustainable carbon sequestration strategies in arid and hyper-arid ecosystems. Overall, these results highlight the importance of deep soil horizons as key carbon reservoirs in hyperarid environments and demonstrate the relevance of Rock-Eval (R) Oxypure for resolving SOC fractions in low-carbon systems.

Plant microbiome is a very wide research area playing a major role in agriculture and plant health. This study investigates the interactions between root-associated bacterial communities and soil physico-chemical characteristics of four Moroccan desert plant species: Lavandula coronopifolia Poir. (n = 20), Lycium intricatum Boiss. (n = 20), Nitraria retusa Asch. (n = 20) and Searsia tripartita (Ucria) Moffett. (n = 20). Soil samples were collected in the rhizosphere of each plant species, and root samples from four different sites, with five random samples per site. Elemental chemical composition of soil sample was analyzed using the X-Ray fluorescence spectrometry and soil carbon, i.e., organic carbon (SOC) and inorganic carbon (SIC) were measured using the Rock–Eval® Oxypure method. Roots were assessed for their microbial community, using the 16S rDNA metabarcoding analysis. Significant variation in soil parameters was observed across sites and among the four desert plant species. SOC and SIC contents were highest in soils associated with S. tripartita, N. retusa, and Ly. intricatum, while La. coronopifolia was associated with elevated levels of Si, Al, K, and Mn. Soil EC was highest in N. retusa and S. tripartita. Microbial analysis revealed that Pseudomonadota and Actinomycetota dominated the root-associated bacterial communities, comprising around 60

Quantifying soil organic and inorganic carbon with a high degree of accuracy is an area of growing scientific interest. There are many methods available for quantifying soil organic carbon (SOC) and soil inorganic carbon (SIC), either separately or simultaneously. Some of these methods present limitations and uncertainties for the quantification of these two forms of soil carbon, particularly in calcareous soils with low SOC contents. Rock‐Eval (RE) thermal analysis, which emerged as a major tool in soil science over the last few decades, has its advantages over other analytical methods, but it also has its limitations, particularly for studying soils with low SOC contents. Here, we propose a new thermal oxidative method with the REdevice to quantify low levels of SOC in calcareous soils: Oxypure. We analyzed soils using both the standard protocol of RE thermal analysis (RE650) and dry combustion using an elemental analyzer (EA) and compared them with the Oxypure method. Our results show that the RE650 protocol is inadequate for studying calcareous soils with low SOC content. Compared to the reference method EA, the Oxypure method is more suitable for quantifying SIC and SOC in calcareous soils with low SOC contents. This study also shows that SOC can be characterized from a combined C–CO 2 thermogram obtained using the Oxypure method. Overall, this study has demonstrated that the Oxypure method is more suitable than the RE650 protocol for studying calcareous soils with low SOC content, and we strongly recommend this method for these particular soils.

In arid regions, excessive water use threatens agricultural sustainability and overall livelihoods. It is essential to minimize water consumption to address these issues. Date palm (Phoenix dactylifera L.) is an emblematic crop of arid regions and a major water consumer. Adapting current irrigation systems to be more water-efficient systems could help cope with the water consumption of this crop. Microbial communities associated with plants are essential for agricultural sustainability and could improve the water use efficiency in regions threatened by water scarcity. These communities should thus be seriously taken into account when adapting agrosystems to the current global change setting. However, no information is presently available on the effects of the different soil water systems on date palm microbial communities. This study highlights the impact of different soil water systems (flooding and drip irrigation, natural conditions and abandoned farms) on date palm root fungal communities at different soil depths (40, 80 and 140 cm deep). The findings revealed that the soil water systems had a marked impact on fungal communities and that drip irrigation reduced the fungal diversity but increased the abundance of arbuscular mycorrhizal fungi. We showed that these effects were similar at all sampling depths. Finally, as the root architecture is a major determinant of water uptake, we reveal different behaviors of the root architecture under these different soil water systems to 160 cm depth. The findings of this study give new insights into the date palm root architecture and associated fungal communities, particularly in the context of the water availability crisis, which drives the adaptation of agricultural systems.

Active restoration structures such as microtopographic water-harvesting designs are widely implemented in dryland ecosystems to improve soil moisture, reduce erosion, and promote vegetation recovery. We assessed the combined effects of planted species identity, planting diversity (mono-, bi- and multi-species mixtures), and micro-catchment (half-moon) structures on seedling performance and spontaneous natural regeneration in a hyper-arid restoration pilot site in Sharaan National Park, northwest Saudi Arabia. Thirteen native plant species, of which four—Ochradenus baccatus, Haloxylon persicum, Haloxylon salicornicum, and Acacia gerrardii—formed the dominant planted treatments, were established in 18 half-moons and monitored for survival, growth, and natural recruitment. Seedling survival after 20 months differed significantly among planting treatments, increasing from 58% in mono-plantings to 69% in bi-plantings and 82% in multi-plantings (binomial GLMM, p < 0.001), indicating a positive effect of planting diversity on establishment. Growth traits (height, collar diameter, and crown dimensions) were synthesized into an Overall Growth Index (OGI) and an entropy-weighted OGI (EW-OGI). Mixed-effects models revealed strong species effects on both indices (F12,369 ≈ 7.2, p < 0.001), with O. baccatus and H. persicum outperforming other taxa and cluster analysis separating “fast expanders”, “moderate growers”, and “decliners”. Trait-based modeling showed that lateral crown expansion was the main driver of overall performance, whereas stem thickening and fruit production contributed little. Between 2022 and 2024, half-moon soils exhibited reduced electrical conductivity and exchangeable Na, higher organic carbon, and doubled available P, consistent with emerging positive soil–plant feedbacks. Spontaneous recruits were dominated by perennials (≈67% of richness), with perennial dominance increasing from mono- to multi-plantings, although Shannon diversity differences among treatments were small and non-significant. The correlation between OGI and spontaneous richness was positive but weak (r = 0.29, p = 0.25), yet plots dominated by O. baccatus hosted nearly two additional spontaneous species relative to other plantings, highlighting its strong facilitative role. Overall, our results show that half-moon micro-catchments, especially when combined with functionally diverse native plantings, can simultaneously improve soil properties and promote biotic facilitation, fostering a transition from active intervention to passive, self-sustaining restoration in hyper-arid environments.

Thymbra nabateorum, a plant species from the Lamiaceae family, is endemic to the Nabatian region, which spans southern Jordan and northwestern Saudi Arabia. It is renowned for its traditional uses and rich phytochemical profile. This study aims to examine the phytochemical composition of T. nabateorum and evaluate its biological activities, including antioxidant capacity, cytotoxic effects on cancer cell lines, and enzyme inhibition relevant to diabetes and neurodegenerative diseases. The essential oil (EO) and methanol extract of T. nabateorum were analyzed using Gas Chromatography–Mass Spectrometry (GC-MS) and High-Performance Liquid Chromatography (HPLC). Antioxidant activity was assessed using the DPPH radical scavenging assay. Cytotoxicity was evaluated against MDA-MB231 and LNCaP cancer cell lines using the MTT assay. Enzyme inhibition assays were conducted to determine the inhibitory effects on α-amylase, α-glucosidase, and butyrylcholinesterase. GC-MS analysis revealed thymol (82.30%) as the major component of the essential oil, while HPLC identified significant phenolic compounds in the methanol extract, including diosmin (118.75 mg/g) and hesperidin (22.18 mg/g). The DPPH assay demonstrated strong antioxidant activity, with the methanol extract showing an IC50 of 11.97 μg/mL for α-amylase and 31.99 μg/mL for α-glucosidase, indicating notable antidiabetic potential. Cytotoxicity tests revealed significant antiproliferative effects against both cancer cell lines, with lower IC50 values compared to standard treatments. T. nabateorum exhibits substantial antioxidant, cytotoxic, and enzyme inhibition activities, supporting its traditional medicinal uses. These findings provide a scientific basis for further research into its bioactive compounds and potential applications in modern pharmacology, particularly in developing natural therapeutic agents for oxidative stress-related diseases and cancer.

Phytogeographic transition zones are often considered areas rich in biodiversity due to their ecological and landscape diversity. This study constitutes the first floristic investigation of the Sharaan Natural Reserve (SNR) located in the northwest of the KSA, which is supposed to be a phytogeographic transition zone due to its location between the central zone of the country dominated by Saharo-Arabic flora and the northern zone characterized by a Mediterranean and Irano-Turanian floristic affinities. The floristic studies carried out in the vegetation season from 2022 to 2024 led to the identification of 166 plant taxa belonging to 38 botanical families. The flora of the SNR is dominated by Therophytes, while the Saharo-Arabian element dominates the chorology of the taxa. The comparative phytogeographic analysis of SNR flora compared to the available literature on published floristic inventories in different phytogeographic regions of the country has confirmed the floristic affinities of the flora of the reserve, especially with the northern and Nefud regions. Among the identified plants, 13 taxa were not mentioned in the 44 consulted references and seem more or less exclusive to the reserve/phytogeographic region. Also, 12 taxa are considered of Least Concern according to the IUCN red list while the presence of Calligonum comosum L’Hér. allows the classification of its natural habitat (dunes) as a Critical Habitat according to the PS6 criteria. This study reports that SNR constitutes a phytogeographic and floristic transitional area by the presence of a significant number of Irano-Turanian (43) and Mediterranean (21) taxa mixed with the dominant Saharo-Arabic species. The SNR region contains a rich and diverse flora due to the biogeographical situation as a transitional zone and the protection due to the closure. This conservation should be strengthened and extended to other neighboring areas with the same biological wealth.

Effective soil characterization is crucial for a better understanding of ecosystem functions and for establishing ecological restoration strategies in degraded areas. However, measuring soil physical and chemical variables is usually cost- and time- consuming, which can be restrictive across large areas. X-ray fluorescence spectroscopy (XRF) has been successfully used for predicting soil variables, but has shown limits for some of them, such as soil texture in hyperarid environments. In this study, we tested the combination of centered log-ratio (CLR) transformation on XRF calculated atomic concentration data and locally weighted partial least squares regression (LWPLSR), for the prediction of soil properties in a hyperarid environment. Soil samples were collected across the AlUla region in Saudi Arabia for XRF spectra acquisition and physico-chemical analysis, such as texture, pH, carbonates content, electrical conductivity, cation exchange capacity (CEC), available macro- and micro-elements content, and soil carbon. LWPLSR construction was based on cross-validation over a calibration dataset to select the optimal number of latent variables. The models’ performances were then evaluated on a validation dataset using the ratio of performance to deviation (RPD) or to inter-quartile (RPIQ), root mean square error of prediction (RMSEP), and the determination coefficient (R²). Accurate predictions were found for clay, silt, and sand content (R² = 0.96, 0.88 and 0.93, respectively), CEC (R² = 0.93), exchangeable CaO, MgO and K2O (R² = 0.89, 0.86 and 0.8, respectively), total carbonates content (R² = 0.81) and soil inorganic carbon (R² = 0.92). These findings highlight the potential of CLR transformation as an effective preprocessing method for XRF data and offer new insights into predicting soil physico-chemical properties in hyperarid environments.

The extent to which past disturbances influence present-day microbial composition and assembly remains poorly understood, especially in extreme environments such as deserts. Using a phylogenetic framework of diversity partitioning, linked to soil composition, we aimed to disentangle the impacts of past disturbance on present-day bacterial and fungal communities, where we also distinguish abundant and rare taxa. Our findings demonstrate that past agricultural activity promoted strong phylogenetic clustering and turnover, accompanied by increased phylogenetic diversity and niche width, reflecting the influence of transient resource availability and niche diversification. Conversely, long-term disturbances reduced phylogenetic diversity and niche width while amplifying selection processes and phylogenetic turnover. These patterns indicate intensified abiotic constraints in this system, where historical contingencies-characterised by enduring drought-wetting cycles-differentially shaped bacterial and fungal communities. Rare taxa were more sensitive to land use and deterministic, while abundant taxa showed broader niche adaptability and stochastic influences, highlighting the need for targeted conservation strategies. This work highlights the critical role of historical disturbances in shaping microbial assembly, provides actionable insights into enhancing desert ecosystem resilience and informing sustainable restoration practices. Si content-a key driver of phylogenetic turnover-could be targeted for ecosystem recovery and conservation strategies in degraded arid regions.

Abstract Soil microbial communities are complex and dynamic, and their composition is jointly driven by niche and neutral processes. Otherwise, the assembly processes of these communities are known to be influenced by both biotic and abiotic factors, yet the extent to which past events could explain their contemporary composition remains unclear, particularly in natural desert environments. We used a phylogenetic framework to quantify the deterministic and stochastic community assembly processes of bacteria and fungi facing historical contingencies linked to past short- and long-term drought-wetting cycles. We found that deterministic and stochastic processes underpinned bacterial community assembly, while fungal communities were mainly assembled via stochastic processes. Abundant bacterial species were at the origin of the differences in phylodiversity noted between natural sites and those facing historical contingencies, while rare fungal species were at the origin of these differences. Furthermore, we showed that historical contingencies increased selection while decreasing dispersal limitation and homogeneous dispersal of bacterial communities. Yet fungal communities were found to be unaffected by past events and their assembly was constantly supported by stochastic processes. These results shed light on the differential impacts of historical contingencies on both bacteria and fungi. They also provide crucial information that could contribute to enhancing desert ecosystem resilience and conservation, and improving our comprehension of soil microbial community assembly in desert ecosystems.

Abstract Hot deserts impose extreme conditions on plants growing in arid soils. Deserts are expanding due to climate change, thereby increasing the vulnerability of ecosystems and the need to preserve them. Arbuscular mycorrhizal fungi (AMF) improve plant fitness by enhancing plant water/nutrient uptake and stress tolerance. However, few studies have focused on AMF diversity and community composition in deserts, and the soil and land use parameters affecting them. This study aimed to comprehensively describe AMF ecological features in a 5,000 m2 arid hyperalkaline region in AlUla, Saudi Arabia. We used a multimethod approach to analyse over 1,000 soil and 300 plant root samples of various species encompassing agricultural, old agricultural, urban and natural ecosystems. Our method involved metabarcoding using 18S and ITS2 markers, histological techniques for direct AMF colonization observation and soil spore extraction and observation. Our findings revealed a predominance of AMF taxa assigned to Glomeraceae, regardless of the local conditions, and an almost complete absence of Gigasporales taxa. Land use had little effect on the AMF richness, diversity and community composition, while soil texture, pH and substantial unexplained stochastic variance drove their structuring in AlUla soils. Mycorrhization was frequently observed in the studied plant species, even in usually non-mycorrhizal plant taxa. Date palms and Citrus trees, representing two major crops in the region, displayed however a very low mycorrhizal frequency and intensity. AlUla soils had a very low concentration of spores, which were mostly small. This study generated new insight on AMF and specific behavioral features of these fungi in arid environments.

Hot deserts impose extreme conditions on plants growing in arid soils. Deserts are expanding due to climate change, thereby increasing the vulnerability of ecosystems and the need to preserve them. Arbuscular mycorrhizal fungi (AMF) improve plant fitness by enhancing plant water/nutrient uptake and stress tolerance. However, few studies have focused on AMF diversity and community composition in deserts, and the soil and land use parameters affecting them. This study aimed to comprehensively describe AMF ecological features in a 5,000 km2 arid hyperalkaline region in AlUla, Saudi Arabia. We used a multimethod approach to analyse over 1,000 soil and 300 plant root samples of various species encompassing agricultural, old agricultural, urban and natural ecosystems. Our method involved metabarcoding using 18S and ITS2 markers, histological techniques for direct AMF colonization observation and soil spore extraction and observation. Our findings revealed a predominance of AMF taxa assigned to Glomeraceae, regardless of the local conditions, and an almost complete absence of Gigasporales taxa. Land use had little effect on the AMF richness, diversity and community composition, while soil texture, pH and substantial unexplained stochastic variance drove these compositions in AlUla soils. Mycorrhization was frequently observed in the studied plant species, even in usually non-mycorrhizal plant taxa (e.g. Amaranthaceae, Urticaceae). Date palms and Citrus trees, representing two major crops in the region, however, displayed a very low mycorrhizal frequency and intensity. AlUla soils had a very low concentration of spores, which were mostly small. This study generated new insight on AMF and specific behavioral features of these fungi in arid environments.

Emblematic Vachellia spp. naturally exposed to hyper-arid conditions, intensive grazing, and parasitism maintain a high nitrogen content and functional mutualistic nitrogen-fixing symbioses. AlUla region in Saudi Arabia has a rich history regarding mankind, local wildlife, and fertility islands suitable for leguminous species, such as the emblematic Vachellia spp. desert trees. In this region, we investigated the characteristics of desert legumes in two nature reserves (Sharaan and Madakhil), at one archaeological site (Hegra), and in open public domains et al. Ward and Jabal Abu Oud. Biological nitrogen fixation (BNF), isotopes, and N and C contents were investigated through multiple lenses, including parasitism, plant tissues, species identification, plant maturity, health status, and plant growth. The average BNF rates of 19 Vachellia gerrardii and 21 Vachellia tortilis trees were respectively 39 and 67

Sampling for Digital Soil Mapping is an expensive and time-constrained operation. It is crucial to consider these limitations in practical situations, particularly when dealing with large-scale areas that are remote and poorly accessible. To address this issue, several authors have proposed methods based on cost constraints optimization to reduce the travel time between sampling sites. These methods focused on optimizing the access cost associated to each sample site, but have not explicitly addressed field work time required for the whole sampling campaign. Hence, an estimation of fieldwork time is of great interest to assists soil surveyors in efficiently planning and executing optimized field surveys. The goal of this study is to propose, implement and test a new method named Multi-Objective Operational Sampling (MOOS), to minimize sampling route time, while ensuring that sample representativeness of the area is maintained. It offers multiple optimal sampling designs, allowing practitioners to select the most suitable option based on their desired sample quality and available time resources. The proposed sampling method is derived from conditioned Latin Hypercube sampling (cLHS) that optimizes both total field work time (travel time and on-site sampling time) and sample representativeness of the study area (cLHS objective function). The use of a multi-objective optimization algorithm (NSGA II) provides a variety of optimal sampling designs with varying sample size. The sampling route time computation is based on an access cost map derived from remote sensing images and expert annotation data. A least-cost algorithm is used to create a time matrix allowing precise evaluation of the time required to connect each pair of sites and thus determine an optimal path. The proposed method has been implemented and tested on sampling for pHH2O mapping within a 651 points kilometric grid in the northern part of Saudi Arabia, where soil analyses were conducted over a 1,069 km2 area. MOOS method was compared to two other common approaches: classical cLHS and cLHS incorporating access cost. The performance of each method was assessed with the cross-validated RMSE and sampling route time in days. Results show that the MOOS method outperforms the two others in terms of sampling route time, especially with increasing sample size, gaining up to 1 day of work for the presented case study. It still ensures a relevant map accuracy and sample representativeness when compared to the two methods. This approach yields promising outcomes for field sampling in digital soil mapping. By simultaneously optimizing both sample representativeness and cost constraints, it holds potential as a valuable decision support tool for soil surveyors facing sampling designs in poorly accessible areas.

Saudi Arabia has implemented ambitious environmental protection programs by creating numerous nature reserves throughout the country. Establishment of the latter nature reserves has led to farm abandonment and the initiation of ecosystem recovery processes. Agricultural practices are known to impact the structure and physicochemical properties of soils while also often markedly affecting natural ecosystem restoration processes. Moreover, weed proliferation in crop fields may modify soil seed banks (SSB), thereby impacting subsequent vegetation recovery. Therefore, it is essential to assess SSB compositions in degraded sites, such as abandoned farms (AF), so as to identify weed species and design efficient restoration strategies in hyperarid ecosystems. In this study, SSB compositions in upper and deep soil layers, standing vegetation compositions, and soil chemical properties were analyzed and compared for two natural ecosystems (NE), two abandoned orchards (AO), two AF, and two natural evaporite basins (EB). NE, AO, AF, and EB all exhibited similar chemical properties, suggesting that former agricultural activities have been guided by a fine understanding of the local environments. Agriculture had impacted the species composition of the observed standing vegetation and germinable SSBs, which could be partly explained by soil property modifications. The findings highlighted that SSBs would warrant detailed study prior to designing ecological restoration strategies, and that the drivers of horizontal and vertical weed dissemination in hyperarid ecosystems should also be explored to gain further insight into weed proliferation patterns and to adapt restoration strategies accordingly.