Larrea Tridentata Research Articles

Impact of Nordihydroguaiaretic Acid on Proliferation, Energy Metabolism, and Chemosensitization in Non-Small-Cell Lung Cancer (NSCLC) Cell Lines.

Lung cancer (LC) is the leading cause of cancer death worldwide. LC can be classified into small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC), with the last subtype accounting for approximately 85% of all diagnosed lung cancer cases. Despite the existence of different types of treatment for this disease, the development of resistance to therapies and tumor recurrence in patients have maintained the need to find new therapeutic options to combat this pathology, where natural products stand out as an attractive source for this search. Nordihydroguaiaretic acid (NDGA) is the main metabolite extracted from the Larrea tridentata plant and has been shown to have different biological activities, including anticancer activity. In this study, H1975, H1299, and A549 cell lines were treated with NDGA, and its effect on cell viability, proliferation, and metabolism was evaluated using a resazurin reduction assay, incorporation of BrdU, and ki-67 gene expression and glucose uptake measurement, respectively. In addition, the combination of NDGA with clinical chemotherapeutics was investigated using an MTT assay and Combenefit software (version 2.02). The results showed that NDGA decreases the viability and proliferation of NSCLC cells and differentially modulates the expression of genes associated with different metabolic pathways. For example, the LDH gene expression decreased in all cell lines analyzed. However, GLUT3 gene expression increased after 24 h of treatment. The expression of the HIF-1 gene decreased early in the H1299 and A549 cell lines. In addition, the combination of NDGA with three chemotherapeutics (carboplatin, gemcitabine, and taxol) shows a synergic pattern in the decrease of cell viability on the H1299 cell line. In summary, this research provides new evidence about the role of NDGA in lung cancer. Interestingly, using NDGA to enhance the anticancer activity of antitumoral drugs could be an improved therapeutic resource against lung cancer.

The LTAR Grazing Land Common Experiment at Walnut Gulch Experimental Watershed.

The Walnut Gulch Experimental Watershed (WGEW) Long-Term Agroecosystem Research (LTAR) network common experiment addresses the aspirational practice of brush management (BM) to reverse the prevailing condition of woody plant encroachment (WPE) and increase perennial native grass production. Across the western United States, the decision to implement BM includes consideration of management objectives, cost, and the expected impact on a diverse suite of ecosystem services. Maintaining or restoring grass cover will help meet the LTAR sustainable production, economic, and social goals, and averting degradation will meet environmental goals. This common experiment, focused on hydrologic and erosion impacts of BM, aims to inform land management decisions on three major plant communities in the Southwestern United States: creosote bush (Larrea tridentata), mesquite (Prosopis velutina), and pinyon-juniper (PJ, Pinus and Juniperus spp.). On the WGEW, applying tebuthiuron pellets to creosote bush increased grass cover and reduced runoff and erosion. The 2016BM experiment on the Santa Rita Experimental Range applied a commonly used liquid herbicide cocktail but achieved only 7% mortality on mesquite, probably because of the timing of the aerial application. Experiments manipulating rainfall amount and intensity on plots receiving fire, chemical, or mechanical BM treatments on PJ communities aim to improve process representation in simulation models. The deliverables of these BM experiments will be to (i) improve the performance of runoff and erosion models, (ii) enhance our ability to identify areas most at risk from reduced hydrologic function and soil erosion after shrub proliferation, and (iii) better predict how landscapes will respond to BM interventions. Ranchers, land management agencies, and watershed conservation organizations will benefit from training and availability of improved tools to focus treatments on areas where greatest net benefits might be realized.

Enhanced Tomato Seed Germination and Seedling Growth Through Oxidative Stress Using Biogenic Silver Nanoparticles

In this study, silver nanoparticles (AgNP) were successfully biosynthesized from Larrea tridentata leaf extract. X-ray Dif fraction (XRD) and Transmission Electron Microscopy (TEM) analysis confirmed that AgNP are crystalline and hemispherical, with sizes between 4 and 26 nm. In addition, the ef fect of nanoparticles on tomato (Solanum lycopersicum) seed germination and seedling growth was examined. Seeds were pre-soaked with dif ferent concentrations of AgNP (0, 4.03, 6.72, 18.66, 51.84, and 86.4 mg L-1). Up to 90% seed germination was achieved at a concentration of at least 4.03 mg L-1, while the control reached below 60%. The highest vigor was obtained at a concentration of 51.84 mg L-1, 2.67 times higher than the vigor of untreated seeds. The synthesized nanoparticles induced activation of tomato seedlings’ defense system against reactive oxidative species, increasing CAT and APX enzyme activities and seedling’s growth. Plumule and radicle length rose 1.49 and 1.98-fold compared to the control. The seedlings were susceptible at 86.4 mg L-1 of AgNP, which af fected all growth parameters and induced oxidative stress response through increased hydrogen peroxide (H2O2) formation and proline content. These provide further insight into the ef fects of biogenic silver nanoparticles on plants during their initial stages of development, demonstrating that these nanoparticles can promote early germination.

Plant-soil microbe feedbacks depend on distance and ploidy in a mixed cytotype population of Larrea tridentata.

Theory predicts that mixed ploidy populations should be short-lived due to strong fitness disadvantages for the rare ploidy. However, mixed ploidy populations are common, suggesting that the fitness costs for rare ploidies are counterbalanced by ecological benefits that emerge when rare. We investigated whether differences in ecological interactions with soil microbes help to maintain a tetraploid-hexaploid population of Larrea tridentata (creosote bush) in the Sonoran Desert, California, United States, where prior work documented ploidy-specific root-associated microbes. We used a plant-soil feedback (PSF) experiment to test whether host-specific soil microbes can alter the outcomes of intraploidy vs. interploidy competition. Host-specific soil microbes can build up over time; thus, distance from a host plant can affect the fitness of nearby plants. Seedlings grown in soils from near plants of a different ploidy produced greater biomass relative to seedlings grown in soils from near plants of the same ploidy. Moreover, seedlings grown in soils from near plants of a different ploidy produced more biomass than those grown in soils that were farther from plants of a different ploidy. These results suggest that the ecological consequences of PSF may facilitate the persistence of mixed ploidy populations. This is the first evidence, to our knowledge, that is consistent with plant-soil microbe feedback as a viable mechanism to maintain the coexistence of multiple ploidy levels in a single population.

Rodents consuming the same toxic diet harbor a unique functional core microbiome

Gut microbiota are intrinsic to an herbivorous lifestyle, but very little is known about how plant secondary compounds (PSCs), which are often toxic, influence these symbiotic partners. Here we interrogated the possibility of unique functional core microbiomes in populations of two species of woodrat (Neotoma lepida and bryanti) that have independently converged to feed on the same toxic diet (creosote bush; Larrea tridentata) and compared them to populations that do not feed on creosote bush. Leveraging this natural experiment, we collected samples across a large geographic region in the U.S. desert southwest from 20 populations (~ 150 individuals) with differential ingestion of creosote bush and analyzed three gut regions (foregut, cecum, hindgut) using16S sequencing and shotgun metagenomics. In each gut region sampled, we found a distinctive set of microbes in individuals feeding on creosote bush that were more abundant than other ASVs, enriched in creosote feeding woodrats, and occurred more frequently than would be predicted by chance. Creosote core members were from microbial families e.g., Eggerthellaceae, known to metabolize plant secondary compounds and three of the identified core KEGG orthologs (4-hydroxybenzoate decarboxylase, benzoyl-CoA reductase subunit B, and 2-pyrone-4, 6-dicarboxylate lactonase) coded for enzymes that play important roles in metabolism of plant secondary compounds. The results support the hypothesis that the ingestion of creosote bush sculpts the microbiome across all major gut regions to select for functional characteristics associated with the degradation of the PSCs in this unique diet.

Acaricide Potential of Creosote Bush (Larrea tridentata) Extracts in the Control of Varroa destructor in Apis mellifera

The aim of the present study was to assess the potential of natural compounds for the control of Varroa destructor in colonies of Apis mellifera, the antimite potential of the hydrolate and ethanolic extract (Leatricina®) of creosote bush (Larrea tridentata) was evaluated at a concentration 50%; contrasting them with the synthetic chemical amitraz and control under in vitro conditions (48 h) and in the hive (52 days). There were differences (p<0.05) in In vitro Varroa mortality with amitraz with higher values (97.9%) compared with hydrolate (53.1%) and Leatricina® (51.5%); Creosote bush extracts were similar (p> 0.05). In the field experiment, the reduction in the percentage of varroa infestation in adult bees was higher 84.9 % (p<0.05) for amitraz, while the hydrolate and Leatricina® showed differences (p<0.05) 49.5 and 72% respectively, the control group showed the lowest values. Even when the effectiveness of synthetic chemicals presents an evident superiority, the average efficacy and other benefits of natural compounds such as creosote bush extracts represent a viable and safe alternative for the control of V. destructor.

Plants from Arid and Semi-Arid Zones of Mexico Used to Treat Respiratory Diseases: A Review.

Medicinal plants have been a traditional remedy for numerous ailments for centuries. However, their usage is limited due to a lack of evidence-based studies elucidating their mechanisms of action. In some countries, they are still considered the first treatment due to their low cost, accessibility, and minor adverse effects. Mexico is in second place, after China, in inventoried plants for medicinal use. It has around 4000 species of medicinal plants; however, pharmacological studies have only been carried out in 5% of its entirety. The species of the Mexican arid zones, particularly in semi-desert areas, exhibit outstanding characteristics, as their adverse growing conditions (e.g., low rainfall and high temperatures) prompt these plants to produce interesting metabolites with diverse biological activities. This review explores medicinal plants belonging to the arid and semi-arid zones of Mexico, focusing on those that have stood out for their bioactive potential, such as Jatropha dioica, Turnera diffusa, Larrea tridentata, Opuntia ficus-indica, Flourensia cernua, Fouquieria splendes, and Prosopis glandulosa. Their extraction conditions, bioactive compounds, mechanisms of action, and biological efficacy are presented, with emphasis on their role in the treatment of respiratory diseases. Additionally, current research, novel applications, and perspectives concerning medicinal plants from these zones are also discussed.

Elevated atmospheric CO2 drives decreases in stable soil organic carbon in arid ecosystems: Evidence from a physical fractionation and organic compound analysis.

The increasing concentration of CO2 in the atmosphere is perturbing the global carbon (C) cycle, altering stocks of organic C, including soil organic matter (SOM). The effect of this disturbance on soils in arid ecosystems may differ from other ecosystems due to water limitation. In this study, we conducted a density fractionation on soils previously harvested from the Nevada Desert FACE Facility (NDFF) to understand how elevated atmospheric CO2 (eCO2 ) affects SOM stability. Soils from beneath the perennial shrub, Larrea tridentata, and from unvegetated interspace were subjected to a sodium polytungstate density fractionation to separate light, particulate organic matter (POM, <1.85 g/cm3 ) from heavier, mineral associated organic matter (MAOM, >1.85 g/cm3 ). These fractions were analyzed for organic C, total N, δ13 C and δ15 N, to understand the mechanisms behind changes. The heavy fraction was further analyzed by pyrolysis GC/MS to assess changes in organic compound composition. Elevated CO2 decreased POM-C and MAOM-C in soils beneath L. tridentata while interspace soils exhibited only a small increase in MAOM-N. Analysis of δ13 C revealed incorporation of new C into both POM and MAOM pools indicating eCO2 stimulated rapid turnover of both POM and MAOM. The largest losses of POM-C and MAOM-C observed under eCO2 occurred in soils 20-40 cm in depth, highlighting that belowground C inputs may be a significant driver of SOM decomposition in this ecosystem. Pyrolysis GC/MS analysis revealed a decrease in organic compound diversity in the MAOM fraction of L. tridentata soils, becoming more similar to interspace soils under eCO2 . These results provide further evidence that MAOM stability may be compromised under disturbance and that SOC stocks in arid ecosystems are vulnerable under continued climate change.

Natural Immunomodulatory Agents as a Complementary Therapy for Poxviruses.

Poxviruses target innate immunity mediators such as tumor necrosis factors, interleukins, interferons, complement, and chemokines. It also targets adaptive immunity such as CD4+ T cells, CD4+ T cells, and B cells. Emerging of the recent epidemic of monkeypox virus (MPXV), a zoonotic disease native to Central and Western Africa, besides the lack of permitted treatments for poxviruses infections, encouraged researchers to identify effective inhibitors to help in preventing and treating poxviruses infections. Natural bioactive components, particularly polyphenolics, are promising for creating powerful antioxidants, anti-inflammatory, immune-stimulating, and antiviral agents. As a result, they are potentially effective therapies for preventing and treating viral diseases, such as infections caused by poxviruses including the recent pandemic MPXV. Polyphenolics: rosmarinic acid, caffeic acid, resveratrol, quercitrin, myricitrin, gingerol, gallotannin, and propolis-benzofuran A, as well as isoquinoline alkaloids: galanthamine and thalimonine represent prospective antiviral agents against MPXV, they can inhibit MPXV and other poxviruses via targeting different viral elements including DNA Topoisomerase I (TOP1), Thymidine Kinase (TK), serine/threonine protein kinase (Ser/Thr kinase), and protein A48R. The bioactive extracts of different traditional plants including Guiera senegalensis, Larrea tridentata, Sarracenia purpurea, Kalanchoe pinnata (Lam.) Pers., Zingiber officinale Roscoe, Quercus infectoria, Rhus chinensis, Prunella vulgaris L., Salvia rosmarinus, and Origanum vulgare also can inhibit the growth of different poxviruses including MPXV, vaccinia virus (VACV), variola virus, buffalopox virus, fowlpox virus, and cowpox virus. There is an urgent need for additional molecular studies to identify and confirm the anti-poxviruses properties of various natural bioactive components, especially those that showed potent antiviral activity against other viruses.

Retraction: Transcriptome characterization of Larrea tridentata and identification of genes associated with phenylpropanoid metabolic pathways.

Retraction: Transcriptome characterization of Larrea tridentata and identification of genes associated with phenylpropanoid metabolic pathways.

Restoring historical grasslands in a desert national park: Resilience or unrecoverable states in an emerging climate?

Ecosystems that supported multiple biological communities during the Holocene and that form alternative stable states pose challenges for identifying appropriate and feasible target communities for ecological restoration and conservation strategies for climate adaptation. In the Chihuahuan Desert, shrubland and perennial grassland alternatively dominated for millennia. However, grassland declined beginning 100–150 years ago during concomitant change in both climate and anthropogenic land use, making it unclear whether restoring grassland is appropriate or feasible in the emerging climate. In Guadalupe Mountains National Park, Texas, USA, we characterized remnant grasslands and performed experiments including outplanting and shrub reduction to assess feasibility and techniques for restoring desert grassland. In remnant patches, grass cover was more temporally variable than shrub cover, as grass cover varied 1.5× between years. Survival of outplanted grasses, either under Larrea tridentata shrubs or in the open with or without woody material encircling outplants for protection, was high (95 %) after seven months but declined to 2 % after 19 months. Response of perennial grass cover was variable after shrub and litter removal on soil surfaces varying in stoniness. Results suggest that 1) restoration can increase native desert grasses but gains may be intermittent; 2) reducing shrubs to facilitate natural expansion of remnant grasses and propagules may be more effective than outplanting grasses; and 3) restoring native grassland by reducing shrubs appears feasible even in dry conditions projected for the emerging climate. Findings that native grasses can increase at least intermittently suggest that practitioners have multiple candidate communities for conservation management and climate change adaptation as grassland, shrubland, and mixed communities each provide unique habitat.

Impact of soil residual auxin herbicide on seedling emergence and biomass differs between soil types, water pulse event, and seedling species

Synthetic‐auxin herbicides are often used to control woody plants and aid in grassland restoration. Seed‐based restoration is common alongside herbicide applications and there may be unintended effects of these herbicides on dryland plants at the seed and seedling stages. Additionally, abiotic conditions at the time of herbicide application may influence herbicide–soil–plant interactions. We conducted a greenhouse study to examine the effects of a common shrub‐control herbicide mix and its interaction with soil type and a post‐herbicide water pulse on common desert plant seeds and seedlings. In this greenhouse study, we found that a subset of species responded negatively to soil residual herbicide activity of a mixture of aminopyralid, clopyralid, and triclopyr at the seed and seedling stages. Species sensitive to soil herbicide residues were primarily shrub and forb species that are often the target species of herbicide applications for woody plant control, such as honey mesquite (Prosopis glandulosa) and creosote bush (Larrea tridentata). However, two shrub species (four‐wing saltbush [Atriplex canescens], soaptree yucca [Yucca elata]) and one perennial grass species (Arizona cottontop [Digitaria californica]), which are used in dryland restoration projects, were found to be particularly sensitive to soil residual herbicide activity. Thus, if using these herbicides to control woody plants and restore herbaceous vegetation via active seeding or relying on the in situ seed bank, considerations should be given to what species are used in the seed mix, what species are already present in the soil seed bank, and other details of the circumstances of herbicide application.

Ecovoltaics: Maintaining Native Plants and Wash Connectivity inside a Mojave Desert Solar Facility Leads to Favorable Growing Conditions

The installation of solar facilities is increasing rapidly in the Mojave Desert USA, with the largest facility in North America (3227 ha) currently being built 30 km north of Las Vegas, NV. At the state level, Nevada (USA) has developed an energy plan to diversify its energy portfolio by 2030 with green energy representing 50% of the energy produced. Although solar is considered a clean energy, it does require significant amounts of land and as such may have negative consequences at the habitat and ecosystem levels. A multi-year study was conducted to assess the impact a photovoltaic facility in the Mojave Desert had on the growth and physiological response of two native shrubs (Ambrosia dumosa and Larrea tridentata) growing inside and outside the facility. These species were selected because they were the dominant species at the site and are representative of desert scrub communities throughout the Mojave Desert. At the time of construction, native plants and washes were left intact inside the solar facility. The solar panel arrays were separated at either 8 m or 10 m. Plants were selected for monitoring on the basis of location: at the panel drip line, below the panels, or midway between panel rows. Abiotic factors, including PAR, reference evapotranspiration, precipitation, soil water in storage, and infiltration, were monitored bi-monthly. The growth and physiological status of the plants were assessed by monitoring leaf water potential, chlorophyll index, canopy temperatures, non-structural carbohydrates in the roots and stems, leaf tissue ion concentrations, stem elongation, and seed production. Plants at the bottom edges of the panels received more precipitation due to runoff from the panels, which led to increased soil moisture in the long spacing but not the short spacing. The lower soil water in storage in the short spacing was related to greater growth and higher soil water extraction. Although the area under the panels provided shade in the summer and warmer temperatures in the winter, the incoming PAR was reduced by as much as 85%, causing plants growing under the panels to be spindly with lower canopy volume (L. tridentata, p = 0.03) and seed yield (A. dumosa, p = 0.05). Ambrosia plants remained green in color year-round (not going into winter dormancy) inside the facility and had elevated levels of starch in their roots and stems compared with plants growing at the outside control sites (p &lt; 0.001). Larrea growing outside the facility had lower xylem water potentials compared with those inside the facility (p &lt; 0.001), lower chlorophyll index (p &lt; 0.001, Ambrosia as well), and lower stem elongation (p &lt; 0.001), supporting the conclusion that both Larrea and Ambrosia performed better inside the facility. Shifts in δ13 C suggested greater water-use efficiency at the locations with the least amount of soil water in storage. Our results support the installation of solar facilities that minimize the impact on native plants and wash connectivity (ecovoltaics), which should translate into a reduced negative impact at the habitat and ecosystem levels. Basedon our results, energy companies that embrace ecovoltaic systems that take an engineering and biological approach should provide acceptable environments for desert fauna. However, corridors (buffers) will need to be maintained between solar facilities, and fences will need to have openings that allow for the continuous flow of animals and resources.

Minimum inhibitory but maximum non-hemolytic concentration of plasma-treated catheters coated with L. tridentata and O. vulgare extracts

Antibacterial extract-coated catheters are promising alternatives to their conventional counterparts, but their hemocompatibility and thermal stability must be studied. Nosocomial bacteria have developed resistance to conventional antibiotics. Herein, the minimum inhibitory but non-hemolytic concentration (MIC-NH) and the thermal stability of Larrea tridentata (L. tridentata) and Origanum vulgare (O. vulgare) extract-coated catheters were studied. Besides, plasma pretreatment was performed to enhance the extract adhesion. Briefly, the extract-coated catheters prevent Staphylococcus aureus colonization without causing hemolysis by using L. tridentata and O. vulgare extracts at MIC-NH (5000 and 2500 μg ml−1, respectively). Moreover, it has been discovered that the extract coating and plasma treatment improved the thermal stability and the extract adhesion, respectively. Thus, this study provides evidence of alternative antibacterial but non-hemolytic extract-coated catheters.

Pathogenicity, virulence and in vitro sensitivity of Elsinoe perseae (= Sphaceloma perseae) isolates to different fungicides

Elsinoe perseae (= Sphaceloma perseae) is the causal agent of the Mancha purpura or scab in avocado (Persea americana). In this study, the pathogenicity and virulence of E. perseae isolates from different agroecological producing areas of Michoacán, Mexico will be reduced. For this, nursery plants with avocado fruits of Flor de María and Méndez varieties were used. On the other hand, the in vitro sensitivity of chemical fungicides (azoxystrobin, thiabendazole, pyraclostrobin, cyprodinil + fludioxonil and azoxystrobin + propiconazole) and authorized for use in orchards with organic management (copper sulfate, copper gluconate, copper oxychloride and the plant extract Larrea tridentata). The observed symptoms of Mancha purpura in the inoculated fruits were corroborated with those described for E. perseae in avocado. Inoculated fruits Flor de María variety shows the highest susceptibility to the pathogen. The isolates of E. perseae presented different degrees of virulence. The isolates showed different in vitro sensitivity values to the fungicides evaluated in the experiment. The pathogen showed the most sensitivity in vitro to chemical fungicides: thiabendazole and azoxystrobin + propiconazole (100% inhibition), and to those authorized in orchards with organic management: L. tridentata and copper oxychloride (on average 58% inhibition).

Minimum inhibitory but maximum non-hemolytic concentration of Larrea tridentata and Origanum vulgare extracts

Larrea tridentata and Origanum vulgare extracts are used in popular medicine to obtain antibacterial compounds to combat bacterial infections. Although the antibacterial activity of L. tridentata and O. vulgare extracts has been reported, hemolytic activity needs to be studied for therapeutic application. This work hypothesized minimum inhibitory but non-hemolytic concentration (MIC-NH) for L. tridentata and O. vulgare extracts. Thus, this study aimed to obtain non-hemolytic crude extracts with antibacterial activity. It was estimated that the MIC-NH of L. tridentata and O. vulgare extracts against the Staphylococcus aureus strain, an important skin pathogen bacterium, were 100 and 75 μg mL-1, respectively. Thus, these in vitro-tested extracts prevented the S. aureus strain growth without provoking hemolysis if the extract concentration was less or equal to the MIC-NH. At the same time, it was determined by gas chromatography coupled with mass spectroscopy that bis-ethylhexyl-phthalate, catechol, encecalinol, isopropyl cinnamate, phenol, guaiacine, and NDGA were antibacterial compounds in the L. tridentata extracts. Meanwhile, for O. vulgare extracts, these compounds were cymene, terpinene, thymol, carvacrol, cimendiol, hexadecanoic acid, bis-ethylhexyl-phthalate, and sitosterol. The findings of this research work must encourage the development of potential biomaterial coatings to replace conventional ones.

Differentiation of rhizosphere fungal assemblages by host ploidy level in mixed‐ploidy Larrea tridentata populations

Polyploidy – whole genome duplication – is common in plants. Studies over the last several decades have documented numerous mixed‐ploidy populations. Whether arising via recurrent whole genome duplication events within a population, or from secondary contact, the persistence of mixed populations is possible by niche differentiation. Specifically, one mechanism facilitating ploidy co‐occurrence is microbially‐mediated niche differentiation (MMND), wherein cytotypes occupy different niches via interactions with different sets of microbes. Inherently cryptic, MMND is underexplored in polyploid plant populations. Here, we search for evidence of MMND in creosotebush Larrea tridentata, a dominant desert shrub of the southwestern US and northern Mexico. We sequenced root‐associated fungal taxa in soils of diploid, autotetraploid, and autohexaploid plants growing in two naturally‐occurring mixed‐cytotype populations. Within populations, we found substantial fungal assemblage overlap across host plant cytotypes. However, using indicator species analysis, we identified some fungi that are differentiated by host plant cytotype, satisfying a necessarycondition for MMND. Future study is needed to determine the degree of niche differentiation conferred, if any, and whether the identified fungi play a role in the long‐term persistence of multiple cytotypes within populations.

Demography and dispersal at a grass‐shrub ecotone: A spatial integral projection model for woody plant encroachment

AbstractThe encroachment of woody plants into grasslands is a global phenomenon with implications for biodiversity and ecosystem function. Understanding and predicting the pace of expansion and the underlying processes that control it are key challenges in the study and management of woody encroachment. Theory from spatial population biology predicts that the occurrence and speed of expansion should depend sensitively on the nature of conspecific density dependence. If fitness is maximized at the low‐density encroachment edge, then shrub expansion should be “pulled” forward. However, encroaching shrubs have been shown to exhibit positive feedbacks, whereby shrub establishment modifies the environment in ways that facilitate further shrub recruitment and survival. In this case there may be a fitness cost to shrubs at low density causing expansion to be “pushed” from behind the leading edge. We studied the spatial dynamics of creosotebush (Larrea tridentata), which has a history of encroachment into Chihuahuan Desert grasslands over the past century. We used demographic data from observational censuses and seedling transplant experiments to test the strength and direction of density dependence in shrub fitness along a gradient of shrub density at the grass–shrub ecotone. We also used seed‐drop experiments and wind data to construct a mechanistic seed‐dispersal kernel, then connected demography and dispersal data within a spatial integral projection model (SIPM) to predict the dynamics of shrub expansion. Contrary to expectations based on potential for positive feedbacks, the shrub encroachment wave is “pulled” by maximum fitness at the low‐density front. However, the predicted pace of expansion was strikingly slow (ca. 8 cm/year), and this prediction was supported by independent resurveys of the ecotone showing little to no change in the spatial extent of shrub cover over 12 years. Encroachment speed was acutely sensitive to seedling recruitment, suggesting that this population may be primed for pulses of expansion under conditions that are favorable for recruitment. Our integration of observations, experiments, and modeling reveals not only that this ecotone is effectively stalled under current conditions but also why that is so and how that may change as the environment changes.

In Vitro Antiviral Activity of Nordihydroguaiaretic Acid against SARS-CoV-2.

The coronavirus infectious disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has been spreading rapidly worldwide, creating a pandemic. This article describes the evaluation of the antiviral activity of nordihydroguaiaretic acid (NDGA), a molecule found in Creosote bush (Larrea tridentata) leaves, against SARS-CoV-2 in vitro. A 35 µM concentration of NDGA was not toxic to Vero cells and exhibited a remarkable inhibitory effect on the SARS-CoV-2 cytopathic effect, viral plaque formation, RNA replication, and expression of the SARS-CoV-2 spike glycoprotein. The 50% effective concentration for NDGA was as low as 16.97 µM. Our results show that NDGA could be a promising therapeutic candidate against SARS-CoV-2.

Consistent microbial and nutrient resource island patterns during monsoon rain in a Chihuahuan Desert bajada shrubland

AbstractIn dryland soils, spatiotemporal variation in surface soils (0–10 cm) plays an important role in the function of the “critical zone” that extends from canopy to groundwater. Understanding connections between soil microbes and biogeochemical cycling in surface soils requires repeated multivariate measurements of nutrients, microbial abundance, and microbial function. We examined these processes in resource islands and interspaces over a two‐month period at a Chihuahuan Desert bajada shrubland site. We collected soil in Prosopis glandulosa (honey mesquite), Larrea tridentata (creosote bush), and unvegetated (interspace) areas to measure soil nutrient concentrations, microbial biomass, and potential soil enzyme activity. We monitored the dynamics of these belowground processes as soil conditions dried and then rewetted due to rainfall. Most measured variables, including inorganic nutrients, microbial biomass, and soil enzyme activities, were greater under shrubs during both wet and dry periods, with the highest magnitudes under mesquite followed by creosote bush and then interspace. One exception was nitrate, which was highly variable and did not show resource island patterns. Temporally, rainfall pulses were associated with substantial changes in soil nutrient concentrations, though resource island patterns remained consistent during all phases of the soil moisture pulse. Microbial biomass was more consistent than nutrients, decreasing only when soils were driest. Potential enzyme activities were even more consistent and did not decline in dry periods, potentially helping to stimulate observed pulses in CO2 efflux following rain events observed at a co‐located eddy flux tower. These results indicate a critical zone with organic matter cycling patterns consistently elevated in shrub resource islands (which varied by shrub species), high decomposition potential that limits soil organic matter accumulation across the landscape, and nitrate fluxes that are decoupled from the organic matter pathways.