Advanced precipitation peak offsets middle growing-season drought in impacting grassland C sink.

Redistribution of precipitation across seasons is a widespread phenomenon affecting dryland ecosystems globally. However, the impacts of shifting seasonal precipitation patterns on carbon (C) cycling and sequestration in dryland ecosystems remain poorly understood. In this study, we conducted a 10-yr (2013-2022) field manipulative experiment that altered the timing of growing-season precipitation peaks in a semi-arid grassland. We found that the delayed precipitation peak suppressed plant growth and thus reduced gross ecosystem productivity, ecosystem respiration, and net ecosystem productivity due to middle growing-season water stress. Surprisingly, shifting more precipitation to the early growing season can advance plant development, increase the dominance of drought-tolerant forbs, and thus compensate for the negative impacts of middle growing-season water stress on ecosystem C cycling, leading to a neutral change in grassland C sink. Our findings indicate that greater precipitation and plant development in spring could act as a crucial mechanism, maintaining plant growth and stabilizing ecosystem C sink. This underscores the urgent need to incorporate precipitation seasonality into Earth system models, which is crucial for improving projections of terrestrial C cycling and sequestration under future climate change scenarios.

Nitrogen availability and summer drought, but not N:P imbalance, drive carbon use efficiency of a Mediterranean tree-grass ecosystem.

All ecosystems contain both sources and sinks for atmospheric carbon (C). A change in their balance of net and gross ecosystem carbon uptake, ecosystem-scale carbon use efficiency (CUEECO), is a change in their ability to buffer climate change. However, anthropogenic nitrogen (N) deposition is increasing N availability, potentially shifting terrestrial ecosystem stoichiometry towards phosphorus (P) limitation. Depending on how gross primary production (GPP, plants alone) and ecosystem respiration (RECO, plants and heterotrophs) are limited by N, P or associated changes in other biogeochemical cycles, CUEECO may change. Seasonally, CUEECO also varies as the multiple processes that control GPP and respiration and their limitations shift in time. We worked in a Mediterranean tree-grass ecosystem (locally called 'dehesa') characterized by mild, wet winters and summer droughts. We examined CUEECO from eddy covariance fluxes over 6 years under control, +N and + NP fertilized treatments on three timescales: annual, seasonal (determined by vegetation phenological phases) and 14-day aggregations. Finer aggregation allowed consideration of responses to specific patterns in vegetation activity and meteorological conditions. We predicted that CUEECO should be increased by wetter conditions, and successively by N and NP fertilization. Milder and wetter years with proportionally longer growing seasons increased CUEECO, as did N fertilization, regardless of whether P was added. Using a generalized additive model, whole ecosystem phenological status and water deficit indicators, which both varied with treatment, were the main determinants of 14-day differences in CUEECO. The direction of water effects depended on the timescale considered and occurred alongside treatment-dependent water depletion. Overall, future regional trends of longer dry summers may push these systems towards lower CUEECO.

Experimentally testing animal responses to prescribed fire size and severity.

Deserts are often highly biodiverse and provide important habitats for many threatened species. Fire is a dominant disturbance in deserts, and prescribed burning is increasingly being used by conservation managers and Indigenous peoples to mitigate the damaging effects of climate change, invasive plants, and land-use change. The size, severity, and patchiness of fires can affect how animals respond to fire. However, there are almost no studies examining such burn characteristics in desert environments, which precludes the use of such information in conservation planning. Using a before-after control-impact approach with 20 sampling sites, we studied the outcomes of 10 prescribed burns of varying size (5-267 ha), severity, and patchiness to identify which variables best predicted changes in small mammal and reptile species richness and abundance. Three of the 13 species showed a clear response to fire. Captures increased for 2 species (1 mammal, 1 reptile) and decreased for 1 species (a reptile) as the proportional area burned around traps increased. Two other mammal species showed weaker positive responses to fire. Total burn size and burn patchiness were not influential predictors for any species. Changes in capture rates occurred only at sites with the largest and most severe burns. No fire-related changes in capture rates were observed where fires were small and very patchy. Our results suggest that there may be thresholds of fire size or fire severity that trigger responses to fire, which has consequences for management programs underpinned by the patch mosaic burning paradigm. The prescribed burns we studied, which are typical in scale and intensity across many desert regions, facilitated the presence of some taxa and are unlikely to have widespread or persistent negative impacts on small mammal or reptile communities in this ecosystem provided that long unburned habitat harboring threatened species is protected.

Prueba experimental de la respuesta animal al tamaño y gravedad de los incendios controlados Resumen Los desiertos suelen contar con mucha biodiversidad y proporcionar hábitats importantes para una variedad de especies amenazadas. El fuego es una perturbación que domina en los desiertos, y los incendios controlados cada vez se usan más por los gestores de la conservación y los pueblos indígenas para mitigar los efectos dañinos del cambio climático, las plantas invasoras y el cambio de uso de suelo. El tamaño, gravedad y fragmentación de los incendios pueden afectar cómo los animales responden al fuego. Sin embargo, casi no existen estudios que analicen dichas características de la quema en los ambientes desérticos, lo que excluye a dicha información de la planeación de la conservación. Usamos una estrategia de antes­después del control­impacto en 20 sitios de muestreo para estudiar los resultados de diez incendios controlados de diferentes tamaños (5­267 ha), gravedad y fragmentación para identificar cuáles variables pronostican mejor los cambios en la riqueza de especies y abundancia de mamíferos pequeños y reptiles. Tres de las 13 especies mostraron una respuesta clara al incendio. Las capturas incrementaron en dos especies (una de mamífero y una de reptil) y disminuyeron en una especie (un reptil) conforme incrementó el área proporcional incendiada alrededor de las trampas. Otras dos especies de mamíferos mostraron respuestas positivas más débiles ante el fuego. El tamaño total y la fragmentación del incendio no fueron influyentes sobre los pronosticadores de cualquier especie. Los cambios en las tasas de captura ocurrieron solamente en los sitios con los incendios más graves y grandes. No observamos cambios relacionados al incendio en las tasas de captura en donde los incendios fueron pequeños y muy fragmentados. Nuestros resultados sugieren que podría haber umbrales del tamaño o gravedad del incendio que provocan las respuestas al fuego, lo que tiene consecuencias para los programas de manejo sustentados en el paradigma del mosaico de fragmentos del incendio. Los incendios controlados que estudiamos, que son típicos en escala e intensidad en muchas regiones desérticas, facilitaron la presencia de algunos taxones y no tuvieron probabilidad de tener un impacto negativo extenso o persistente sobre las comunidades de mamíferos pequeños y reptiles en este ecosistema, siempre y cuando se proteja el hábitat que lleva mucho tiempo sin incendios y en donde viven las especies amenazadas.

Distinct microbial communities under different rock-associated microhabitats in the Qaidam Desert.

Hypolithic communities, which occupy highly specialised microhabitats beneath translucent rocks in desert and arid environments, have assembly mechanisms and ecosystem functions are not fully understood. Thus, in this study, we aimed to examine the microbial community structure, assembly, and function of light-accessible (under quartz, calcite, and hypolithic lichen-dominated biocrusts) and light-inaccessible microhabitats (under basalt and adjacent soil) in the Qaidam Desert, China. The results showed that hypolithic communities have different characteristics compared with microbial communities of light-inaccessible microhabitats. Notably, hypolithic bacterial communities were dominated by Cyanobacteria, whereas light-inaccessible microhabitats showed a predominance of Bacteroidetes and Proteobacteria. Although the class Dothideomycetes (phylum: Ascomycota) dominated the fungal communities between the two microhabitat types, Sordariomycetes were more prevalent in light-accessible microhabitats. Network and robustness analyses showed that hypolithic communities were less complex and more resilient than microbial communities in light-inaccessible microhabitats. Our results indicated that deterministic processes, specifically homogeneous selection, govern the establishment of bacterial and fungal communities in light-accessible and light-inaccessible microhabitats. The hypolithic community showed an increased frequency of phylotypes that exhibited increased tolerance to functional stress response pathways. In contrast to light-inaccessible microhabitats, light-accessible microhabitats showed a slight decrease and a notable increase in the prevalence of carbon fixation pathways in prokaryotes and carbon fixation in photosynthetic organisms, respectively. For fungi, light-accessible microhabitats enriched saprotrophic and ectomycorrhizal groups. These results highlight the importance of complex and diverse microhabitats in desert regions, which serve as vital shelters for microbes. Combining future research on interactions between hypolithic communities and environments may enhance our current understanding of their pivotal roles in sustaining desert ecosystems. This knowledge then be applied to design and implement informed conservation efforts to preserve these unique rock-associated microhabitats in desert ecosystems.

Comparison of aboveground vegetation and soil seed bank composition at sites of different grazing intensity around a savanna-woodland watering point in West Africa.

Grazing removes a plant's aboveground vegetative and reproductive tissues and can modify the soil seed bank, potentially impacting the restoration of preferred species. Knowledge about aboveground vegetation and species composition of soil seed bank and the processes that contribute to vegetation recovery on and surrounding watering points subjected to grazing is lacking. Successful restoration strategies hinge on addressing these knowledge gaps. We assessed the effects of livestock grazing on aboveground vegetation and soil seed bank characteristics along a river bank and surrounding areas subject to different grazing intensities and draw implications for restoration. Plots (50 × 50 m) were established along five transects representing differing levels of grazing intensity. Soil samples were taken from three layers within each plot to determine soil properties and species composition of soil seed bank using the seedling emergence method. Heavy grazing resulted in the disappearance of perennial grasses, a reduction in species diversity and a decrease in soil nutrients with increased soil depth. Overall, the similarity between the extant aboveground vegetation and flora within the soil seed bank was low. The soil seed bank was dominated by herbaceous species and two woody species, suggesting that many woody species are not accumulating in the soil. With increasing soil depth, the seed density and richness declined. Canonical correspondence analyses (CCAs) showed that emerged seedlings from the soil seed bank were significantly influenced by soil carbon, organic matter, total nitrogen, total potassium and soil cation exchange capacity. This finding suggests that current grazing practices have a negative impact on the vegetation surrounding watering points; hence there is a need for improved grazing management strategies and vegetation restoration in these areas. The soil seed bank alone cannot restore degraded river banks; active transfer of propagules from adjacent undisturbed forest areas is essential.

Combing both simulated and field-measured data to develop robust hyperspectral indices for tracing canopy transpiration in drought-tolerant plant.

Transpiration plays a key role in water and energy fluxes at various scales. While in recent remote sensing offers a fast and convenient method for tracing transpiration at multiple scales, the approach is mostly indirect and relies on energy balance. Although several hyperspectral indices have been reported to show potentials for tracing transpiration directly, both at leaf and canopy scales, they remain in pioneer stages and need extensive validations. In this study, we used the Soil, Canopy Observation, Photochemistry and Energy fluxes (SCOPE) model calibrated to arid ecosystems in Central Asia, to generate a simulated dataset for validation. Furthermore, new and robust indices have been developed by combining both simulated and in situ measured datasets. Results suggested that the SR(1525, 2150), ND(1425, 2145), and previously reported index of dSR(660,1040) have significant relationships with both simulated and in situ measured transpiration. Further analyses revealed that the ND(1425,2145) shows consistent performance, even with different methodologies of combining simulation and field-measured datasets. Statistically significant results were obtained in this study, even for a dominant drought-tolerant species in arid land, a place that typically has weak vegetation reflectance under strong background radiation. We foresee the approach being conducted in other regions where vegetation reflectance dominates. This may lead to robust hyperspectral indices being developed for directly tracing transpiration at various scales.

Pulse frequency and soil-litter mixing alter the control of cumulative precipitation over litter decomposition.

Macroclimate has traditionally been considered the predominant driver of litter decomposition. However, in drylands, cumulative monthly or annual precipitation typically fails to predict decomposition. In these systems, the windows of opportunity for decomposer activity may rather depend on the precipitation frequency and local factors affecting litter desiccation, such as soil-litter mixing. We used a full-factorial microcosm experiment to disentangle the relative importance of cumulative precipitation, pulse frequency, and soil-litter mixing on litter decomposition. Decomposition, measured as litter carbon loss, saturated with increasing cumulative precipitation when pulses were large and infrequent, suggesting that litter moisture no longer increased and/or microbial activity was no longer limited by water availability above a certain pulse size. More frequent precipitation pulses led to increased decomposition at high levels of cumulative precipitation. Soil-litter mixing consistently increased decomposition, with greatest relative increase (+194%) under the driest conditions. Collectively, our results highlight the need to consider precipitation at finer temporal scale and incorporate soil-litter mixing as key driver of decomposition in drylands.

The use of spatial empirical models to estimate soil erosion in arid ecosystems.

The central objective of this project was to utilize geographical information systems and remote sensing to compare soil erosion models, including Modified Pacific South-west Inter Agency Committee (MPSIAC), Erosion Potential Method (EPM), and Revised Universal Soil Loss Equation (RUSLE), and to determine their applicability for arid regions such as Kuwait. The northern portion of Umm Nigga, containing both coastal and desert ecosystems, falls within the boundaries of the de-militarized zone (DMZ) adjacent to Iraq and has been fenced off to restrict public access since 1994. Results showed that the MPSIAC and EPM models were similar in spatial distribution of erosion, though the MPSIAC had a more realistic spatial distribution of erosion and presented finer level details. The RUSLE presented unrealistic results. We then predicted the amount of soil loss between coastal and desert areas and fenced and unfenced sites for each model. In the MPSIAC and EPM models, soil loss was different between fenced and unfenced sites at the desert areas, which was higher at the unfenced due to the low vegetation cover. The overall results implied that vegetation cover played an important role in reducing soil erosion and that fencing is much more important in the desert ecosystems to protect against human activities such as overgrazing. We conclude that the MPSIAC model is best for predicting soil erosion for arid regions such as Kuwait. We also recommend the integration of field-based experiments with lab-based spatial analysis and modeling in future research.

Carbon stock and its responses to climate change in Central Asia.

Central Asia has a land area of 5.6 × 10(6) km(2) and contains 80-90% of the world's temperate deserts. Yet it is one of the least characterized areas in the estimation of the global carbon (C) stock/balance. This study assessed the sizes and spatiotemporal patterns of C pools in Central Asia using both inventory (based on 353 biomass and 284 soil samples) and process-based modeling approaches. The results showed that the C stock in Central Asia was 31.34-34.16 Pg in the top 1-m soil with another 10.42-11.43 Pg stored in deep soil (1-3 m) of the temperate deserts. They amounted to 18-24% of the global C stock in deserts and dry shrublands. The C stock was comparable to that of the neighboring regions in Eurasia or major drylands around the world (e.g. Australia). However, 90% of Central Asia C pool was stored in soil, and the fraction was much higher than in other regions. Compared to hot deserts of the world, the temperate deserts in Central Asia had relatively high soil organic carbon density. The C stock in Central Asia is under threat from dramatic climate change. During a decadal drought between 1998 and 2008, which was possibly related to protracted La Niña episodes, the dryland lost approximately 0.46 Pg C from 1979 to 2011. The largest C losses were found in northern Kazakhstan, where annual precipitation declined at a rate of 90 mm decade(-1) . The regional C dynamics were mainly determined by changes in the vegetation C pool, and the SOC pool was stable due to the balance between reduced plant-derived C influx and inhibited respiration.

Three new species of arbuscular mycorrhizal fungi discovered at one location in a desert of Oman: Diversispora omaniana, Septoglomus nakheelum and Rhizophagus arabicus.

Three new species of arbuscular mycorrhizal (AM) fungi (Glomeromycota) were isolated from soil samples collected from a hyperarid sandy plain of South Arabia. Morphological characteristics of the spores clearly differentiated them from closely related AM species. Molecular analyses were performed on rDNA sequences obtained from single spores including a ~1700 bp region comprising partial SSU, ITS, partial LSU and the ~600 bp ITS region only. The phylogenetic trees based on these regions showed that the three species belong to well described genera but are clearly distinct from known species. Consequently, we describe them here as Diversispora omaniana, Septoglomus nakheelum and Rhizophagus arabicus spp. nov. D. omaniana and R. arabicus were isolated from the native, arid habitat, while S. nakheelum was isolated from a nearby irrigated date palm plantation. The discovery of three new species of AM fungi from this location suggests that a number of additional undescribed AM taxa may be present in such desert ecosystems. Further work to understand the diversity and functional significance of these new AM taxa may offer new opportunities for conservation, re-vegetation, and sustainable agriculture in extremely arid environments.

The Activity Patterns and Grouping Characteristics of the Remaining Goitered Gazelle (Gazella subgutturosa) in an Isolated Habitat of Western China.

Wildlife activity patterns, which reveal the daily allocation of time and energy, are crucial for understanding survival pressures, adaptive strategies, and behavioral characteristics in different environments. Among ungulates, grouping behavior is a prevalent adaptive trait that reflects the population structure, mating systems, and life history strategies formed over long-term evolutionary processes. This study aimed to elucidate the daily activity patterns and grouping characteristics of the rare goitered gazelle (Gazella subgutturosa) in the Helan Mountains of western China from 2022 to 2023 using camera trap monitoring. With a total of 3869 camera days of effective trapping, we recorded 442 independent detections of goitered gazelles. The results revealed the following: (1) Goitered gazelle is primarily active during the day, showing an activity pattern similar to crepuscular animals, with two activity peaks occurring after dawn and before dusk. (2) Daily activity patterns showed both seasonal and sex differences. In the warm season, morning activity peaks occurred earlier, and afternoon peaks occurred later compared to the cold season. The overlap in daily activity patterns between females and males in the warm season was lower than that in the cold season, and this trend persisted throughout the year. (3) The number of times different types of groups were observed varied significantly, with single males and single females accounting for a larger proportion of all observed groups. There was no significant difference in group size across seasons, with groups typically consisting of 1-2 individuals. Our study provides detailed insights into the temporal ecology and population structure of goitered gazelles in arid and semi-arid ecosystems. This information will guide the identification of future conservation priorities and the development of management plans for the reserve.

Impact of meteorological variability on diurnal and seasonal net ecosystem productivity in a desert riparian forest ecosystem.

The desert riparian forests are susceptible to meteorological changes and contribute significantly to the net ecosystem productivity (NEP) variations of arid ecosystems. However, the responsive patterns of their NEP variations to the meteorological variabilities remain inadequately comprehended. To address this gap, we utilized seven years of eddy covariance flux measurements in a representative desert riparian forest to investigate the NEP variations and its response to changing meteorological factors across diverse temporal scales. The results revealed significant periodic variations in half-hourly NEP, with dominant cycles spanning from five hours to one year, with a principal oscillation period of one day. Key meteorological factors including global solar radiation (Rg), relative humidity (RH), air temperature (Ta), soil temperature (Ts), and vapor pressure deficit (VPD) exhibited synchronization with NEP on daily scales. This synchronization, coupled with the observed one-day periodic NEP variations, provides robust evidence supporting the existence of a circadian rhythm in the ecosystem carbon exchange of desert riparian forest regulated by meteorological conditions. Seasonal patterns were significant in the impact of Rg phase, Ta diurnal amplitude, and VPD diurnal amplitude on NEP diurnal amplitude and phase. The NEP diurnal amplitude significantly, directly, and positively affected daily NEP in both the dormant and growing seasons, whereas its phase yielded significant negative effects (P< 0.05). The averages, amplitudes, and phases of diurnal meteorological conditions controlled the daily NEP by regulating NEP diurnal amplitude and phase. These findings provide evidence that the variability in circadian rhythms, caused by the increase in diurnal Ta and VPD, significantly impact the daily NEP at an ecosystem scale. This study enriches our comprehension of the meteorological mechanisms governing diurnal and seasonal carbon uptake dynamics within desert riparian forests, providing fresh insights into the direct and indirect roles of climate change in shaping patterns of ecosystem carbon exchange.

Spatiotemporal Mechanisms of the Coexistence of Reintroduced Scimitar-Horned Oryx and Native Dorcas Gazelle in Sidi Toui National Park, Tunisia.

Examining the distribution patterns and spatiotemporal niche overlap of sympatric species is crucial for understanding core concepts in community ecology and for the effective management of multi-species habitats within shared landscapes. Using data from 26 camera-traps, recorded over two years (December 2020-November 2022), in Sidi Toui National Park (STNP), Tunisia, we investigate habitat use and activity patterns of the scimitar-horned oryx (n = 1865 captures) and dorcas gazelle (n = 1208 captures). Using information theory and multi-model inference methods, along with the Pianka index, we evaluated the habitat characteristics influencing species distribution and their spatial niche overlap. To delineate daily activity patterns, we applied kernel density estimation. Our findings indicate minimal spatial overlap and distinct environmental factors determining suitable habitats for each species. Furthermore, we found significant temporal niche overlaps, indicative of synchrony in daily activity patterns, with both species showing peak activity at dawn and dusk. Our results indicated that oryx and gazelle differ in at least one dimension of their ecological niche at the current density levels, which contributes to their long-term and stable coexistence in STNP.

Shifting patterns in fine root distribution of four xerophytic species across soil structural gradients and years of growth.

Fine root (diameter < 2 mm) distribution influences the potential for resource acquisition in soil profiles, which defines how plants interact with local soil environments; however, a deep understanding of how fine root vertical distribution varies with soil structural variations and across growth years is lacking. We subjected four xerophytic species native to an arid valley of China, Artemisia vestita, Bauhinia brachycarpa, Sophora davidii, and Cotinus szechuanensis, to increasing rock fragment content (RFC) treatments (0%, 25%, 50%, and 75%, v v-1) in an arid environment and measured fine root vertical profiles over 4 years of growth. Fine root depth and biomass of woody species increased with increasing RFC, but the extent of increase declined with growth years. Increasing RFC also increased the degree of interannual decreases in fine root diameter. The limited supply of soil resources in coarse soils explained the increases in rooting depth and variations in the pattern of fine root profiles across RFC. Fine root depth and biomass of the non-woody species (A. vestita) in soil profiles decreased with the increase in RFC and growth years, showing an opposite pattern from the other three woody species. Within woody species, the annual increase in fine root biomass varied with RFC, which led to large interannual differences in the patterns of fine root profiles. Younger or non-woody plants were more susceptible to soil environmental changes than the older or woody plants. These results reveal the limitations of dry and rocky environments on the growth of different plants, with woody and non-woody plants adjusting their root vertical distribution through opposite pathways to cope with resource constraints, which has management implications for degraded agroforest ecosystems.

Potential benefits and risks of solar photovoltaic power plants on arid and semi-arid ecosystems: an assessment of soil microbial and plant communities.

Exponential increase in photovoltaic installations arouses concerns regarding the impacts of large-scale solar power plants on dryland ecosystems. While the effects of photovoltaic panels on soil moisture content and plant biomass in arid ecosystems have been recognized, little is known about their influence on soil microbial communities. Here, we employed a combination of quantitative PCR, high-throughput sequencing, and soil property analysis to investigate the responses of soil microbial communities to solar panel installation. We also report on the responses of plant communities within the same solar farm. Our findings showed that soil microbial communities responded differently to the shading and precipitation-alternation effects of the photovoltaic panels in an arid ecosystem. By redirecting rainwater to the lower side, photovoltaic panels stimulated vegetation biomass and soil total organic carbon content in the middle and in front of the panels, positively contributing to carbon storage. The shade provided by the panels promoted the co-occurrence of soil microbes but inhibited the abundance of 16S rRNA gene in the soil. Increase in precipitation reduced 18S rRNA gene abundance, whereas decrease in precipitation led to decline in plant aboveground biomass, soil prokaryotic community alpha diversity, and dehydrogenase activity under the panels. These findings highlight the crucial role of precipitation in maintaining plant and soil microbial diversities in dryland ecosystems and are essential for estimating the potential risks of large-scale solar power plants on local and global climate change in the long term.

Biotic interactions contribute more than environmental factors and geographic distance to biogeographic patterns of soil prokaryotic and fungal communities.

Recent studies have shown distinct soil microbial assembly patterns across taxonomic types, habitat types and regions, but little is known about which factors play a dominant role in soil microbial communities. To bridge this gap, we compared the differences in microbial diversity and community composition across two taxonomic types (prokaryotes and fungi), two habitat types (Artemisia and Poaceae) and three geographic regions in the arid ecosystem of northwest China. To determine the main driving factors shaping the prokaryotic and fungal community assembly, we carried out diverse analyses including null model, partial mantel test and variance partitioning analysis etc. The findings suggested that the processes of community assembly were more diverse among taxonomic categories in comparison to habitats or geographical regions. The predominant driving factor of soil microbial community assembly in arid ecosystem was biotic interactions between microorganisms, followed by environmental filtering and dispersal limitation. Network vertex, positive cohesion and negative cohesion showed the most significant correlations with prokaryotic and fungal diversity and community dissimilarity. Salinity was the major environmental variable structuring the prokaryotic community. Although prokaryotic and fungal communities were jointly regulated by the three factors, the effects of biotic interactions and environmental variables (both are deterministic processes) on the community structure of prokaryotes were stronger than that of fungi. The null model revealed that prokaryotic community assembly was more deterministic, whereas fungal community assembly was structured by stochastic processes. Taken together, these findings unravel the predominant drivers governing microbial community assembly across taxonomic types, habitat types and geographic regions and highlight the impacts of biotic interactions on disentangling soil microbial assembly mechanisms.

Biocrusts mediate the plant community composition of dryland restoration ecosystems.

Degradation and expansion are current threats associated with drylands. During natural or artificial restoration, dryland ecosystems tend to contain a unique community, namely, biocrusts. Studies have shown that biocrusts serve multiple functions and have the potential to accelerate or inhibit degradation. However, the mechanisms by which biocrusts mediate dryland plant community structure and composition remain largely unknown. In this study, we performed a series of pot experiments under greenhouse conditions at three disturbance levels (strong, moderate and no disturbance) and at three rainfall gradients (- 50 %, normal, + 50 %) for different biocrust types. Our objective was to examine how biocrusts influence the introduction and establishment of different functional forms of plant species during the different succession stages of dryland recovery. Our results showed that biocrusts have significantly different effects on the seed germination and survival of the tested plant species. Although strong disturbances to the biocrusts and increasing rainfall alleviated the inhibitory effects of biocrusts on the perennial herb (S. glareosa) and subshrub (C. latens) species, these factors could only promote the temporary survival of these two plants in the revegetated area. These results indicate that biocrusts in revegetated systems play important sieving functions during plant species establishment. Additionally, the survival of S. viridis, a plant species with small seeds adapted to the current habitat, was promoted in the community, but two plant species that are currently unsuitable, S. glareosa and C. latens, were filtered out by the biocrusts. Our conclusions suggest that biocrusts play an ecological filtering role in plant species introduction and establishment in revegetated ecosystems and demonstrate the scientific significance of biocrusts in maintaining the health and stability of dryland ecosystems.

A novel approach for long-term spectral monitoring of desert shrubs affected by an oil spill.

Crude oil pollution is a global environmental concern since it persists in the environment longer than most conventional carbon sources. In December 2014, the hyper-arid Evrona Nature Reserve, Israel, experienced large-scale contamination when crude oil spilled. The overarching goal of the study was to investigate the possible changes, caused by an accidental crude oil spill, in the leaf reflectance and biochemical composition of four natural habitat desert shrubs. The specific objectives were (1) to monitor the biochemical properties of dominant shrub species in the polluted and control areas; (2) to study the long-term consequences of the contamination; (3) to provide information that will assist in planning rehabilitation actions; and (4) to explore the feasibility of vegetation indices (VIs), along with the machine learning (ML) technique, for detecting stressed shrubs based on the full spectral range. Four measurement campaigns were conducted in 2018 and 2019. Along with the various stress indicators, field spectral measurements were performed in the range of 350-2500 nm. A regression analysis to examine the relation of leaf reflectance to biochemical contents was carried out, to reveal the relevant wavelengths in which polluted and control plants differ. Vegetation indices applied in previous studies were found to be less sensitive for indirect detection of long-term oil contamination. A novel spectral index, based on indicative spectral bands, named the "normalized blue-green stress index" (NBGSI), was established. The NBGSI distinguished significantly between shrubs located in the polluted and in the control areas. The NBGSI showed a strong linear correlation with pheophytin a. Machine learning classification algorithms obtained high overall prediction accuracy in distinguishing between shrubs located in the oil-polluted and the control sites, indicating internal component differences. The findings of this study demonstrate the efficacy of indirect and non-destructive spectral tools for detecting and monitoring oil pollution stress in shrubs.

The Impact of Different Types of Hydrocarbon Disturbance on the Resiliency of Native Desert Vegetation in a War-Affected Area: A Case Study from the State of Kuwait.

This study assesses the impact of total petroleum hydrocarbon (TPH) concentration and soil parameters (heavy metals, chemical properties, and water-soluble boron) on the succession process of vegetation survival in the Al-Burgan oil field in Kuwait. A total of 145 soil samples were randomly collected from the three main types of hydrocarbon contamination, including dry oil lake (DOL), wet oil lake (WOL), and tarcrete. Sampling was also extended to noncontaminated bare soils that were considered reference sites. Remote-sensing data from Sentinel-2 were also processed to assess the level of contamination in relation to soil surface cover. The results showed that TPH concentration was significantly higher in WOL and DOL (87,961.4 and 35,740.6 mg/kg, respectively) compared with that in tarcrete (24,063.3 mg/kg), leading to a significant increase in soil minerals and heavy metals, greater than 50 mg/kg for Ba, and 10 mg/kg for V, Zn, Ni, and Cr. Such high concentrations of heavy metals massively affected the native vegetation's resiliency at these sites (<5% vegetation cover). However, vegetation cover was significantly higher (60%) at tarcrete-contaminated sites, as TPH concentration was lower, almost similar to that in uncontaminated areas, especially at subsurface soil layers. The presence of vegetation at tarcrete locations was also associated with the lower concentration of Ba, V, Zn, Ni, and Cr. The growth of native vegetation was more likely related to the low concentration of TPH contamination at the subsurface layer of the soils in tarcrete sites, making them more suitable sites for restoration and revegetation planning. We concluded that further investigations are required to provide greater insight into the native plants' phytoextraction potential and phytoremediation.

Experimental Analysis of Interactions Among Saprotrophic Fungi from A Phosphorous-Poor Desert Oasis in the Chihuahuan Desert.

Fungal ecological interactions play a key role in structuring community assemblages. These associations may involve both antagonistic and synergistic relationships, which are commonly influenced by abiotic factors such as nutrient conditions. However, information for extreme, oligotrophic systems remain poor. Herein, interactions among key members of the aquatic transient fungal community (Aspergillus niger, Cladosporium sp., and Coprinellus micaceus) of a low-nutrient freshwater system in the Cuatro Ciénegas Basin, Mexico were studied. Pairwise interaction bioassays were explored in vitro under different nutrient conditions, including carbohydrates-rich, carbohydrates and amino peptides-rich, and low nutrients. Our results indicated that antagonistic patterns prevail among the studied taxa. However, nutrient-dependent changes were observed in Cladosporium sp. shifting to synergy under carbohydrates-rich conditions, suggesting changes in the fungal community composition as a result of nutrient enrichment. Remarkably, our findings contrast with previous work demonstrating mainly synergistic interactions between our tested fungal isolates and co-occurring autochthonous bacteria (Aeromonas spp. and Vibrio sp.) under low-nutrient conditions. This observation may indicate that bacteria and fungi exhibit distinct community-level responses, driven by nutrient conditions. This contributes to the knowledge of fungal community dynamics and interspecific interactions in an oligotrophic ecosystem, highlighting the relevance of nutrient-based shifts and antagonistic interactions in ecosystem dynamics.