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Atmospheric aridity and soil drought control vegetation water use and affect the terrestrial water and carbon cycles. Separating these two types of drought is difficult but crucial because they relate to different ecosystem properties and their impacts depend on vegetation types. We examine how well satellite-observed solar-induced chlorophyll fluorescence (SIF) captures the drought responses of taiga and steppe in semiarid areas on the Mongolian plateau, which have experienced a historic drought since the late 1990s. Ten-year records of the GOSAT SIF and the MODIS-band-1 photochemical reflectance index (PRI, also known as chlorophyll/carotenoid index) from Aqua consistently suggest that the taiga is sensitive to vapor-pressure deficit but insensitive to surface-soil drought, and that the opposite is the case for the steppe. The MODIS PRI changes reasonably with temperature and drought stress, and also with canopy shades, which is attributable to the xanthophyll cycle. However the most influential factor on the PRI is leaf area in both vegetations, and temperature is the second in the taiga, indicating the dominant effect of its pigment-pool size. The leaf area index of the taiga has almost similar values and seasonal patterns in each year, while the SIF shows remarkable interannual changes. The SIF yield in the taiga decreases 36–48% on average with the increase of vapor-pressure deficit from 1 kPa to 3 kPa under high-PRI conditions. Almost all detectable information from the SIF yield in the steppe is correlated with PRI on a monthly basis. The SIF in the steppe decreases nonlinearly when the surface-soil-water content fell below ∼0.154 m3 m−3, which agrees well with an eddy-covariance result in this region and implies the capability of satellite-based wilting-point estimation. We will further clarify which biological factors affected the observed results of SIF and PRI using the process-based model 'Soil-Canopy-Observation of Photosynthesis and Energy fluxes' (SCOPE) and show the impact of drought on the gross primary production in the past decade.

Unmanned Aerial Vehicles (UAVs) have started to receive more attention in the ecological field in the past 15 years, as they provide very high-resolution imagery that ranges from meters to millimeters. Very high-resolution multispectral imagery obtained from UAVs can help in assessing and monitoring native desert vegetation. Thus, this study use UAVs to develop a method to estimate the biomass and carbon stock of native desert shrubs. The method integrates different techniques and software to monitor native plants' coverage, biomass, and carbon stock. The techniques used in this work are also applicable for other native desert shrubs in the region and could support ecosystem managers in assessing and monitoring arid ecosystems and restoration and revegetation programs. A three-stage image and data management are discussed, including: (1) fieldwork and image acquisition using UAVs, (2) image pre-processing, and (3) image processing using different techniques and software.•Determining shrub biomass is not restricted to multispectral data only but could be applicable for RGB data since it mainly depends on the DSM and DTM.•Allometric parameters could help in estimating desert shrub biomass which could be measured easily and rapidly using UAV imagery.•SVM Supervised classification could help in distinguishing between native shrubs and grasses., Graphical abstract Image, graphical abstract

Changes in hydro-geomorphic connectivity have been previously linked to catastrophic shifts in landscape structures and function leading to irreversible degradation. Here we present evidence and new observations to better understand the link between connectivity of water and sediments and possible phase transitions for the case of semiarid ecosystems at the catchment and hillslope scales. We first focus on rangelands, where coevolving vegetation and landform structures lead to a distinct connectivity pattern responsible for the healthy functioning of the system. Positive feedbacks, triggered by disturbances in vegetation, water or sediment structures can alter the hydro-geomorphic connectivity leading to degradation. Our results for rangelands in Australia, from both simulations and observations, suggest that an increase in connectivity beyond a threshold may lead to irreversible degradation, meaning that the system return to a functional state is unlikely without extensive management interventions. We also analyse the case of semi-arid floodplain wetlands of the Murray-Darling Basin, where we observe that dis-connectivity during droughts promote terrestrial vegetation encroachment and degradation. Simulations and observations also indicate the presence of thresholds beyond which the recovery of the system is unlikely without interventions.

Current climate change scenarios project altered rainfall frequencies which boosts scientific interest in ecosystems' responses to prolonged dry conditions. Under less rainfall, NRWI may play an increasingly important role, Yet, only sparse data are available to assess the role of non-rainfall water input (NRWI) during times of low water availability across ecoregions. Particularly, soil water vapor adsorption has received little attention at field scale. This term is used for the phase change of water from gas to liquid at highly negative matric potential. Under such conditions, water condensates already at relative humidity < 100%. The process has been broadly studied in laboratories but little is known from field experiments, which rarely cover periods longer than one month. Yet, several studies report soil water uptake from the atmosphere during soil surface cooling and in the early mornings. Lysimeters have played a strong role in quantifying these NRWI. Eddy Covariance (EC) measurements, in contrast, are known for their limited data quality under nighttime conditions when a stable boundary layer hinders the turbulent exchange of mass and energy. Therefore, EC has not been tested yet to trace soil adsorption. In this contribution we adapt a methodology to derive NRWI from lysimeters data and compare them to EC measurements. We focus mainly on adsorption and evaluate the consistency between adsorption estimated with the lysimeters and negative (downward) latent heat (LE) fluxes from EC. We apply the method to a data set that comprises three years of observations from a semi-arid Spanish tree grass ecosystem. Our results show that during the dry season the gradient in water vapour established between the atmosphere (more humid) and the soil pores (more dry) leads to adsorption by the soil. The observations from both instruments suggest that during the dry season, nightly transport of humidity from the atmosphere towards the ground is driven by soil vapor adsorption. This process occurs each night typically in the second half, but begins increasingly earlier in the evening the dryer the conditions are. The amount of water adsorbed is not directly comparable between EC and the lysimeter readings. With the latter, we quantified a yearly mean uptake between 8.8 mm and 25 mm per year. With the lysimeters we measure additionally 23.1 mm of water that condenses as dew and fog in winter, when EC is impeded by stable conditions. We further analyze EC LE measurements from different sites to evaluate if adsorption can be detected from EC data collected at different locations.We conclude that the temporal patterns of adsorption estimates from lysimeters match the nighttime negative LE data from the EC technique, although the absolute numbers are uncertain. This might open interesting perspective to fill the knowledge gap of the role of soil water vapor adsorption from the atmosphere at field scale and open the opportunity to broaden the topic across ecosystem research communities. Our results also highlight a potential shortcoming in the interpretation of EC measurements in the case that negative nighttime values, representing physically plausible adsorption, are neglected.

The reliable and consistent remote sensing-based drought indices along with Geographic Information System (GIS) play a significant role in the mapping, and monitoring of agricultural drought. The core objective of the present study is to monitor agricultural drought dynamics over the semi-arid Rayalaseema region of Peninsular India during the year 2000 to 2018 by using the Normalized Vegetation Supply Water Index (NVSWI) derived from time-series remote sensing data products. NVSWI is the normalization of Vegetation Supply Water Index (VSWI), which was computed by integrating the Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST). The analysis of Standardized Precipitation Index (SPI) shows that in dry year (2001), majority of the study area experienced extreme dry conditions (SPI

In arid and semiarid ecosystems, digging and burrowing are common behaviors in many mammals looking for shelter, food, thermoregulation, etc. Many rodents, as tuco-tucos, may use both the foreclaws and incisors – according to soil requirements – to accomplish that goal in an effective manner. Although digging represents a low fraction of the daily energy budget, it triggered some highly derived adaptations. Forelimbs in caviomorph scratch-diggers are characterized by highly robust humeri and ulnae, and well-developed bony superstructures. These mechanically advantageous traits have been already found during early ontogeny in Ctenomys –compensating the lower muscular development – and encompass the gradual improvement of digging and burrowing behaviors on those stages. This fact would provide enough time to reach a proper musculoskeletal and behavioral development, to deal with energetic and biomechanical demands. Gross head morphology, instead, has proven to conserve a rodent already-optimized bauplan among caviomorphs, by not showing a more mechanically advantageous masticatory apparatus in tuco-tucos. Their strong bite forces –which cover both tooth-digging and a wide range of social needs – would be a consequence of the hypertrophied and fiber types-wise specialized jaw adduct musculature. Despite corresponding soil reaction forces may injure animals’ skull or teeth, ctenomyid skull geometry, bone distribution, and incisors microstructure evolved to withstand the high stress and abrasion. Thus, yet inconclusively, animal’s performance can be fairly predicted based on biomechanics.

Semiarid ecosystems of Chile with Mediterranean climate support high demographic rates and maintain important economies associated with the productivity of the natural environment; however, they strongly depend on the water availability and their future is compromised by climate variations. This study tries to define the role of hydrological variables on the growth of herbaceous biomass under the current climate and under future weather variations. For this, the authors used meteorological stations which let them estimate the water balance at plot scale and spectral reflectance sensors which let them follow the dynamics of the NDVI of herbaceous plants. In this context, the NDVI value was about 0.7, which means approximately 3700 kg DM ha1. However, under the worst-case climate change scenarios (RCP 8.5), annual precipitation showed a reduction of up to 31.6% regarding the present period. In this situation, the NDVI could be reduced up to 80% respect to the current situation. Thus, if climate changes to its worst scenario, it could threaten the maintenance and productivity of these ecosystems.

El conocimiento de la biodiversidad de los sírfidos (Diptera: Syrphidae) en las zonas semiáridas de México, es muy limitado, sobre todo, al relacionado con las cactáceas en descomposición. Este estudio aporta un inventario faunístico de los sírfidos del género Copestylum asociados a los tejidos en descomposición de los cactus de matorrales crasicaules en dos Reservas de la Biosfera, “Barranca de Metztitlán” (RBBM) y “Tehuacán-Cuicatlán” (RBTC), ambas situadas en el centro de México. Se analiza la diversidad y composición de especies de sírfidos en ambas reservas y se documenta la especie de cactus a la que se asocian las larvas de estos dípteros durante la época de lluvias. El método de recolecta fue mediante búsqueda directa de estados inmaduros que se desarrollan en tejidos de cactáceas en descomposición. Se obtuvieron 137 ejemplares de sírfidos pertenecientes a 10 especies entre las dos reservas estudiadas. Los resultados indican que no existen diferencias significativas en la riqueza de especies entre ambas reservas, pero sí hay diferencia al comparar la diversidad de orden q2. En la RBBM, la especie dominante fue Copestylum latum, mientras que Copestylum posticum fue la especie dominante en la RBTC. La especie de cactus determina la segregación de sírfidos en cada reserva. En la RBBM, las especies de sírfidos se asociaron a las especies de cactus Isolatocereus dumortieri y Myrtillocactus geometrizans, mientras que, en la RBTC fueron Neobuxbaumia mezcalensis, Pachycereus hollianus y Myrtillocactus geometrizans. Biodiversity knowledge of syrphids (Diptera: Syrphidae) from the semiarid environments of Mexico is still limited; particularly, those associated to the decaying cactus. In this study, we provide an inventory of the syrphid species from two Biosphere Reserves in the semiarid zones of central Mexico. We compare the diversity and species composition of syrphids through both Biosphere Reserves and we documented the host cactus species of syrphids during the rainy season. Larvae were sampled by hand searching on decayed cacti tissues. We recorded a total of 137 individuals of syrphids and 10 species between the two studied Biosphere Reserves. Our results revealed that there are not significant differences in species richness between RBBM and RBTC but there were significant differences in species diversity of order q2. We found that Copestylum latum was the dominant syrphid at RBBM whereas Copestylum posticum was dominant across the RBTC. The cactus species is presumably determining the species segregation of syrphids. In the RBBM, syrphid were associated to the cacti Isolatocereus dumortieri and Myrtillocactus geometrizans; meanwhile, in the RBTC syrphids were associated to Neobuxbaumia mezcalensis, Pachycereus hollianus and Myrtillocactus geometrizans.

Представлены основные физико-химические и водно-физические свойства псаммофитных почв аридных экосистем Убсу-Нурской котловины. Приведены количественные характеристики температурных полей псаммофитных почв, полученных на основе совместного анализа временных рядов наземного температурного мониторинга и спутниковых данных., There are presented the main physicochemical and water-physical properties of psammophytic soils of the Ubsu-Nur hollow arid ecosystems. Provided the quantitative characteristics of the temperature fields obtained on the basis of a joint analysis of time series of ground-based temperature monitoring and satellite data.

С учетом климатических, почвенных и агроэкологических реалий Юга России был разработан рабочий протокол клонального микроразмножения представителей родов Caragána и Cersis в целях защитного ле- соразведения. Процесс клонального микроразмножения включает в себя 4 этапа: процедуру выбора расте- ния-донора для получения хорошо растущей стерильной культуры, лабораторное масштабирование мери- стематических клонов, укоренение размноженных побегов и выращивание растений в условиях теплицы перед высадкой в открытый грунт. Конкретные этапы были соотнесены как с культуральными особенно- стями растений, так и со спецификой их дальнейшего обитания в аридной зоне практически без помощи со стороны человека, но при наличии высокой антропогенной нагрузки в результате примыкающего зем- лепользования. Данный протокол является особенно актуальным для Волгоградской области и обладает новизной, поскольку впервые используются данные виды растений для клонального микроразмножения, и рассматривается процесс их подготовки к естественному произрастанию, выбранные растения могут жить в аридных условиях, без дополнительного внесения влаги., Taking into account the climatic, soil and agroecological realities of the South of Russia, a working protocol for clonal micropropagation of representatives of the genera Caragána and Cersis for protective afforestation was developed. The clonal micropropagation process includes 4 stages: the procedure for selecting a donor plant to obtain a well-growing sterile culture, laboratory scaling of meristematic clones, rooting of propagated shoots and growing plants in a greenhouse before planting in open ground. Specific stages were correlated both with the cultural characteristics of plants and with the specifics of their further habitation in the arid zone with practically no human assistance, but in the presence of a high anthropogenic load as a result of adjacent land use. This protocol is especially relevant for the Volgograd region and has a novelty, since for the first time these plant species are used for clonal micropropagation, and the process of their preparation for natural growth is considered, the selected plants can live in arid conditions, without additional introduction of moisture., Научно-агрономический журнал, Выпуск 1 (112) 2021, Pages 40-44

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.

The native vegetation communities in the sagebrush steppe, a semi-arid ecosystem type, are under threat from exotic annual grasses. Exotic annual grasses increase fire severity and frequency, decrease biodiversity, and reduce soil carbon storage amongst other ecosystem services. The invasion of exotic annual grasses is causing detrimental impacts to land use by eliminating forage for livestock and creating a huge economic cost from fire control and post-fire restoration. To combat invasion, land managers need to know what exotic annual grasses are present, where they are invading, and estimates of their biomass. Mapping exotic annual grasses is challenging because many areas in the sagebrush steppe are difficult to access; yet field measurements are the main method to identify and quantify their existence. In this study, we address this challenge by exploring the use of both landscape-scale and plot-scale observations with remote sensing. First, we use satellite imagery to map where exotic annual grasses are invading and identify the native species which are being encroached upon. Second, we investigate the use of fine-scale imagery for non-destructive measurements of biomass of exotic annual grasses. Understanding the location of exotic annual grasses is important for restoration efforts, e.g. large swath (~100m) herbicide spraying. Restoration efforts are expensive and often ineffective in areas already dominated by exotic annual grasses. Early detection of exotic annual grasses in sagebrush and native grasses communities will increase the chances of effective ecosystem restoration. We used Sentinel-2 satellite imagery in Google Earth Engine, a cloud computing platform, to train a random forest (RF) machine learning algorithm to map vegetation in ~150,000 acres in the sagebrush steppe in southeast Idaho. The result is a classification map of vegetation (overall accuracy of 72%) and a map of percent cover of annual grass (R2 = 0.58). The combination of these two maps will allow land managers to target areas of restoration and make informed decisions about where to allow grazing. In addition to knowing what exotic annual grasses exist and their percent cover, detailed information about their biomass is important for understanding fuel loads and forage quality. Structure from Motion (SfM) is a photogrammetry technique that uses digital images to develop 3-dimensional point clouds that can be transformed into volumetric measurements of biomass. The SfM technique has the potential to quantify biomass estimates across multiple plots while minimizing field work. We developed allometric equations relating SfM-derived volume (m3) to biomass (g/m2) for a study area in southeast Oregon. The resulting equation showed a positive relationship (R2 = 0.51) between the log transformed SfM-derived volume and log transformed biomass when litter was removed. This relationship shows promise in being upscaled to larger surveys using aerial platforms. This method can reduce the need for destructively harvesting biomass, and thus allow field work to cover a greater spatial extent. Ultimately, increasing spatial coverage for biomass will improve accuracy in quantifying fuel loads and carbon storage, providing insights to how these exotic plants are altering ecosystem services.

The effect of non-uniform solar radiation over opposing hillslopes leads to aspect-controlled vegetation patterns in semi-arid ecosystems. It creates a differentiation in soil properties and vegeta...

Ecosystems in drylands are highly susceptible to changes in their way of functioning due to extreme and prolonged droughts or anthropogenic perturbation. Long-standing pressure, from climate or human action, may result in severe alterations in their dynamics. Moreover, changes in dryland ecosystems functioning can take place abruptly (Horion et al., 2016). Such abrupt changes may have severe ecological and economic consequences, disturbing the livelihood of drylands inhabitants and causing increased poverty and food insecurity. Considering that drylands cover 40% of Earth’s land surface and are home to around one-third of the human population, detecting and characterizing hotspots of abrupt changes in ecosystem functioning (here called turning points) becomes even more crucial.BFAST, a time series segmentation technique, was used to detect breakpoints in time series (1982-2015) of rain-use efficiency. An abrupt change in rain-use efficiency time series points towards a significant change in the way an ecosystem responds to precipitation, allowing the study of turning points in ecosystem functioning in both natural and anthropogenic landscapes. Moreover, we here proposed a new typology to characterize turning points in ecosystem functioning, which takes into account the trend in ecosystem functioning before and after the turning point, as well as differences in the rate of change. Case studies were used to evaluate the performance of the new typology. Finally, ancillary data on population density and drought were used to have some first insights about the potential determinants of hotspots of turning point occurrence.Our results showed that 13.6% of global drylands presented a turning point in ecosystem functioning between 1982 and 2015. Hotspots of turning point occurrence were observed in North America (where 62.6% of the turning points were characterized by a decreasing trend in ecosystem functioning), the Sahel, Central Asia, and Australia. The last three hotspot regions were mainly characterized by a positive trend in ecosystem functioning after the turning point. The ancillary data pointed to an influence of both droughts and human action on turning point occurrence in North America, while in Asia and Australia turning point occurrence was higher in areas with higher anthropogenic pressure. In the grasslands of the Sahel, turning points were potentially related to drought. By detecting where and when hotspots of turning points occurred in recent decades, and by characterizing the trends in ecosystem functioning before and after the turning points, we advanced towards better supporting decision making related to ecosystems conservation and management in drylands. Moreover, we provided first insights about the drivers of ecosystem functioning change in hotspots of turning point occurrence in global drylands (Bernardino et al., 2019). References:Bernardino PN, De Keersmaecker W, Fensholt R, Verbesselt J, Somers B, Horion S (2019) Global-scale characterization of turning points in arid and semi-arid ecosystems functioning. Manuscript submitted for publication.Horion S, Prishchepov A V., Verbesselt J, de Beurs K, Tagesson T, Fensholt R (2016) Revealing turning points in ecosystem functioning over the Northern Eurasian agricultural frontier. Global change biology, 22, 2801–2817.

Foliar water uptake (FWU) has been reported for different species across several ecosystems types. However, little attention has been given to arid ecosystems, where FWU during dew formation or small rain events could ameliorate water deficits. FWU and their effects on leaf water potential (ΨLeaf) were evaluated in grasses and shrubs exploring different soil water sources in a Patagonian steppe. Also, seasonal variability in FWU and the role of cell wall elasticity in determining the effectson ΨLeaf were assessed. Eleven small rain events (< 8 mm) and 45 days with dew formation were recorded during the study period. All species exhibited FWU after experimental wetting. There was a large variability in FWU across species, from 0.04 mmol m−2 s−1 in species with deep roots to 0.75 mmol m−2 s−1 in species with shallow roots. Species-specific mean FWU rates were positively correlated with mean transpiration rates. The increase in ΨLeaf after leaf wetting varied between0.65 MPa and 1.67 MPa across species and seasons. The effects of FWU on ΨLeaf were inversely correlated with cell wall elasticity. FWU integrated over both seasons varied between 28 mol m−2 in species with deep roots to 361 mol m−2 in species with shallow roots. Taking into account the percentage of coverage of each species, accumulated FWU represented 1.6% of the total annual transpiration of grasses and shrubs in this ecosystem. Despite this low FWU integrated over time compared to transpiration, wetting leaves surfaces can help to avoid larger water deficit during the dry season. Fil: Cavallaro, Agustin. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina Fil: Carbonell Silleta, Luisina. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina Fil: Pereyra, Daniel A.. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina Fil: Goldstein, Guillermo Hernan. University of Miami; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Scholz, Fabian Gustavo. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina Fil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina

Across North America, interannual variability (IAV) in gross primary production (GPP) and net ecosystem exchange (NEE), and their relationship with environmental drivers, are poorly understood. Her...

Biological soil crusts (BSCs) in arid region provide critical ecosystem services. However, most previous studies on BSC–plant topic have had a narrow spatiotemporal and taxonomic focus, so context dependency concerning exotic plant responses to BSCs remains poorly understood. In this study, using a series of manipulative experiments under greenhouse conditions, we investigated the influence of BSCs in the Tengger Desert in northern China on seed germination and seedling growth of an exotic grass species, Stipa glareosa P. Smirn., with or without two native plants species, Eragrostis poaeoides Beauv. and Artemisia capillaris Thunb., both of whose ontogeny differs from that of the exotic species. BSC treatments included intact crusts, disturbed crusts, and bare soil. Compared to bare soil, the presence of BSCs reduced the germination of E. poaeoides and A. capillaris by 78% and 74%, respectively. For the exotic species, BSCs reduced the germination percentage by as much as 90%. With gradual increases in soil nutrients such as organic carbon, available phosphorus, and available nitrogen, the shoot biomass of the three plants increased along the sequence from bare soil to lichens and mosses. Shoot biomass of the two native plant species was reduced by the exotic species S. glareosa. The percent germination and shoot biomass of S. glareosa on the disturbed crusts were greater than those on the intact crusts and bare soils. Overall, the presence of BSCs on stabilized sand dunes can reduce the germination of these three plant species, but compared with native plant species, BSCs have a stronger inhibitory effect on the seed germination of the exotic plant species. However, the disturbance may weaken the inhibition of the seed germination of the exotic grass S. glareosa and may provide more nutrients for the exotic grass S. glareosa to establish a revegetation region. We concluded that compared with the absence of BSCs, BSCs in this desert ecosystem can provide more nutrients and a suitable environment for native vascular plants and exert an inhibitory effect on the exotic plants.

In search of generalities in biological invasions, it is sometimes forgotten that invader success can be a function of both the diversity of the invaded community and the relatedness of the invader relative to community residents. Both qualities are likely to be especially important in stressful ecosystems, and identifying the species and community attributes that influence biological invasions can help direct management efforts in a sensitive ecosystem like those in arid regions. Pink Morning Glory, Ipomoea carnea Jaq. (Family: Convolvulaceae), is an annual vine native to Central and South America and is invasive in Egypt. We examined the performance of I. carnea at different densities in assembled communities of Egyptian annual native species. The native plant communities were manipulated to represent gradients of species richness and phylogenetic diversity and relatedness to I. carnea . We quantified the performance of I. carnea in these communities and examined the contribution of resident species richness, phylogenetic diversity, and phylogenetic relatedness to invader resistance. Our findings revealed that there was a positive relationship between invader performance and its mean phylogenetic distance to the resident species. Furthermore, species‐rich communities with more distantly related species positively contributed to invader performance in contrast to the classic biotic resistance hypothesis. Beyond these positive relationships, a positive density‐dependent effect of I. carnea on its performance was observed. We conclude that facilitative interactions are potentially important drivers promoting the successful invasion of the nonnative species I. carnea in water‐limited and harsh ecosystems. These results suggest that perhaps contrary to understanding from temperate systems, communities with a higher diversity of species could be more likely to be invaded by arid‐adapted species that are distantly related to natives. Thus, policy and management in arid regions should carefully consider reviewing the importation of nonnative species that are phylogenetically distinct and adapted to arid conditions and prioritizing their control once they are established.