Pollination Biology and Life History Traits of the Rare Las Vegas Bear Poppy (Arctomecon californica).

Arctomecon californica, the Las Vegas bear poppy, is a rare plant found only in the eastern Mojave Desert of North America. Because of recent declines in the populations of this endemic plant, conservationists are currently seeking protection for A. californica under the US Endangered Species Act. In this study, we investigated the natural history of A. californica and documented insect visitors potentially pollinating A. californica in Clark County, Nevada. We find that the populations of A. californica fluctuate from year to year, with many populations declining by over 90% from 2021 to 2022. The pollinator communities of A. californica also vary from year to year. In some years, specialist bees in the genus Perdita make up the majority of pollinators, while in other years, generalist bees like Apis mellifera and Hylaeus dominate. Furthermore, we confirm what previous work has suggested, that A. californica requires pollinators to set seed, yet not all insect visitors are good pollinators. This work provides useful natural history information about the Las Vegas bear poppy, which will be informative to conservationists designing strategies to protect this imperiled species.

Potential extinction cascades in a desert ecosystem: Linking food web interactions to community viability.

Desert communities are threatened with species loss due to climate change, and their resistance to such losses is unknown. We constructed a food web of the Mojave Desert terrestrial community (300 nodes, 4080 edges) to empirically examine the potential cascading effects of bird extinctions on this desert network, compared to losses of mammals and lizards. We focused on birds because they are already disappearing from the Mojave, and their relative thermal vulnerabilities are known. We quantified bottom-up secondary extinctions and evaluated the relative resistance of the community to losses of each vertebrate group. The impact of random bird species loss was relatively low compared to the consequences of mammal (causing the greatest number of cascading losses) or reptile loss, and birds were relatively less likely to be in trophic positions that could drive top-down effects in apparent competition and tri-tropic cascade motifs. An avian extinction cascade with year-long resident birds caused more secondary extinctions than the cascade involving all bird species for randomized ordered extinctions. Notably, we also found that relatively high interconnectivity among avian species has formed a subweb, enhancing network resistance to bird losses.

Snake venom cysteine-rich secretory protein from Mojave rattlesnake venom (Css-CRiSP) induces acute inflammatory responses on different experimental models.

Snake venoms contain various molecules known for activating innate immunity and causing local effects associated with increased vascular permeability, such as vascular leakage and edema, common symptoms seen in snakebite envenomings. We have demonstrated that snake venom cysteine-rich secretory proteins (svCRiSPs) from North American pit vipers increase vascular permeability. This study aimed to explore the functional role of CRiSP isolated from Mojave rattlesnake (Crotalus scutulatus scutulatus) venom (Css-CRiSP) on the activation of inflammatory responses in different models. We measured the release of inflammatory mediators in cultured human dermal blood endothelial cells (HDBEC), lymphatic endothelial cells (HDLEC) and monocyte-derived macrophages (MDM) at 0.5, 1, 3, 6, and 24 h after treatment with Css-CRiSP (1 µM). We also determined the acute inflammatory response in BALB/c mice 30 min after intraperitoneal injection of the toxin (2 µg/mouse). Css-CRiSP induced the production of IL-8 and IL-6, but not TNF-α, in HDBEC and HDLEC in a time-dependent manner. In addition, Css-CRiSP significantly enhanced the production of IL-6, TNF-α, IL-8, and IL-1ß in MDM. Moreover, it caused a remarkable increase of chemotactic mediators in the exudates of experimental mice. Our results reveal that Css-CRiSPs can promote a sustained release of inflammatory mediators on cell lines and an acute activation of innate immunity in a murine model. These findings contribute to the growing body of evidence supporting the involvement of svCRiSPs in the augmentation of envenomation effects, specifically, the role of svCRiSPs in inducing vascular dysfunction, initiating early inflammatory responses, and facilitating the activation of leukocytes and releasing mediators. These findings will lead to a better understanding of the pathophysiology of envenoming by Mojave rattlesnakes, allowing the development of more efficient therapeutic strategies.

Wildfire and cattle legacies on gradients of soil nitrogen underlie patterns of annual brome invasion.

Human activities are increasing wildfires and livestock activity in arid ecosystems with potential implications for the spread of invasive grasses. The objective of this study was to test whether fire history and cattle activity alter soil resource gradients, thereby affecting patterns of Bromus rubens L. (red brome) invasion. Six paired burned and unburned transect lines (1-km long) were established in the northeast Mojave Desert along the boundaries of four independent wildfire scars. At 100-m transect increment points, we measured the distance to the two nearest cowpats, and two random points and measured the density, height, biomass, and seed production of red brome, soil moisture and inorganic nitrogen (N). Cattle activity was 29% greater along burned transects compared to unburned transects (P < 0.05). Red brome height, density, and seed production were 11-34% greater along burned transects than unburned transects (P < 0.05). Red brome height, biomass, density, and seed production were twofold to tenfold greater next to cowpats compared to random points (P < 0.05). Soils along burned transects and beneath cowpats had greater soil inorganic N (P < 0.05), which was positively correlated with red brome density, height, biomass, and seed production (R2 = 0.60-0.85, P < 0.0001). Transgenerational effects were evident as seeds from red brome next to cowpats had 27% higher germination than seeds collected from random points. Positive responses of red brome to increased inorganic N related to fire and cattle activity may contribute fine fuel infill that drives invasive grass-fire cycles in deserts.

Evolution of the Xerocarpa clade (Opuntia; Opuntieae): Evidence for the Role of the Grand Canyon in the Biogeographic History of the Iconic Beavertail Cactus and Relatives.

The formation of the western North American drylands has led to the evolution of an astounding diversity of species well adapted for such communities. Complex historical patterns often underlie the modern distribution of the flora and fauna of these areas. We investigated the biogeography of a group of desert-adapted prickly pears, known as the Xerocarpa clade, from western North America. The Xerocarpa clade originated in the mid-late Pliocene, likely on the Colorado Plateau, and then moved south into the Mojave, Sonoran, and Chihuahuan deserts, and California montane regions, further diversifying, mostly into the Quaternary. The southward trajectory of the clade was likely greatly influenced by the formation of the Grand Canyon. The synapomorphy of dry fruit presumably impeded the long-distance dispersibility of the beavertail cactus, Opuntia basilaris, while dry, spiny fruit may have enabled O. polyacantha to substantially increase its distribution. Opuntia basilaris evolved a pubescent epidermis, allowing it to invade hotter, drier conditions, while the spine-clothed stems of O. polyacantha may have given it an advantage for increasing its northern range into colder environments. The Xerocarpa clade shows a cold desert origin, and changes in morphological characters have made these sister taxa well adapted for invading broadscale, but oftentimes contrasting habitats.

Species delimitation, biogeography, and natural history of dwarf funnel web spiders (Mygalomorphae, Hexurellidae, Hexurella) from the United States / Mexico borderlands.

The rarely encountered spider genus Hexurella Gertsch & Platnick, 1979 includes some of the smallest mygalomorph spiders in the world, with four poorly known taxa from central and southeastern montane Arizona, southern California, and northern Baja California Norte. At time of description the genus was known from fewer than 20 individuals, with sparse natural history information suggesting a vagrant, web-building, litter-dwelling natural history. Here the first published taxonomic and natural history information for this taxon is provided in more than 50 years, working from extensive new geographic sampling, consideration of male and female morphology, and sequence capture-based nuclear phylogenomics and mitogenomics. Several new species are easily diagnosed based on distinctive male morphologies, while a complex of populations from central and northern Arizona required an integrative combination of genomic algorithmic species delimitation analyses and morphological study. Four new species are described, including H.ephedrasp. nov., H.uwiiltilsp. nov., H.xericasp. nov., and H.zassp. nov. Females of H.encina Gertsch & Platnick, 1979 are also described for the first time. It is predicted that additional new species will ultimately be found in the mountains of central and northwestern Arizona, northern mainland Mexico, and the Mojave Desert of California.

Long-term seed bank persistence in a stochastic desert environment.

Seed banks, the collection of viable seeds in the soil, are particularly important determinants of population survival in highly variable environments. Predictions of increased stochasticity in the amount and timing of precipitation in desert environments raise the question of how seed banks of desert species will respond to climate change, and ultimately, whether these species will persist. Here, we present data from our long-term studies of germination requirements and seed bank dynamics in a rare desert gypsophile perennial, Arctomecon californica (Las Vegas bearpoppy). Arctomecon californica is a relatively short-lived plant that recruits from seed in sequences of unusually favorable years. We used germination experiments, an in situ seed bank study, and a 15-year field seed retrieval study to examine factors affecting seed bank persistence. In the germination study, a majority of seeds remained dormant, despite a wide variety of treatments, suggesting that a large proportion of the seed dispersed each year has cue-nonresponsive dormancy. Our in situ seed bank study showed that seed density varied widely between sites, among transects, and among samples within a transect. The patchiness of seeds in the soil highlights the importance of protecting large areas where A. californica populations are known to have existed in the past. The seed retrieval study provided strong evidence that this species has a long-lived seed bank in which only a small fraction of seeds (roughly 5%) become nondormant each year, allowing seed banks of this species to last up to 20 years without a seed production event. Whether this impressive life-history strategy can maintain the species in the face of climate change depends on the future frequency of the well-timed precipitation that allows for the establishment of new cohorts of adult plants.

Neurotoxic respiratory failure absent following Arizona rattlesnake bites.

Warnings of neurotoxic respiratory paralysis following envenomation by rattlesnakes (Crotalus sp.) have been included in numerous scholarly publications over the past 60 years, resulting in fear and anxiety in the public and among clinicians. We examine the validity of the widespread belief that rattlesnakes in the arid southwestern United States, and particularly the Mohave Rattlesnake (Crotalus scutulatus), pose a significant risk of medically relevant respiratory weakness and paralysis in humans. A retrospective review of 3440 suspected rattlesnake bites reported to the Arizona Poison and Drug Information Center between 1999 and 2020 produced no evidence of respiratory weakness in a region with three species known to express significant amounts of neurotoxin in their venoms: Crotalus concolor, C. tigris, and the more widely distributed C. scutulatus. A literature review produced numerous warnings regarding respiratory paralysis following envenomation by rattlesnakes in our region that either lacked references or cited sources that did not contain strong supportive data. We found no case reports of neurotoxic respiratory weakness following Arizona rattlesnake bites in the literature and such reports in surrounding states were scant. We conclude that neurotoxic respiratory failure in this region following rattlesnake envenomation is extraordinarily rare. All rattlesnake bites should receive the same consideration and critical care, and warnings about significant risk of respiratory failure are unwarranted, regardless of species involved.

Mojavia aguilerae and M. dolomitestris - two new Nostocaceae (Cyanobacteria) species from the Americas.

While nostocacean cyanobacteria are ubiquitous and play critical roles in terrestrial ecosystems, their taxonomy and biogeography still entail mysteries. We isolated two Nostoc-like cyanobacteria from biological soil crusts of the Atacama (Chile) and Mojave (USA) Deserts. An initial 16S rRNA gene phylogeny placed both in monophyly with Mojavia pulchra. Here, we describe two new species of the previously monotypic Mojavia using a polyphasic approach including morphology, 16S rRNA phylogenies, secondary structure, and percent similarity of the 16S-23S ITS region. Like M. pulchra, both new species produce compact microcolonies, arthrospore-like akinetes, and monocytes, traits characteristic of the genus. Mojavia aguilerae sp. nov. is morphologically distinct from both other species in producing bluntly conical end cells, abundant enlarged akinetes in multiseriate filaments, and gold-colored cells during senescence. Mojavia dolomitestris sp. nov. exhibited distinctly firm, light-colored, compartmentalized mucilage. M. dolomitestris is somewhat cryptic with M. pulchra, but has more densely packed microcolonies, rarity and later onset of brownish sheath pigmentation, and an origin from soils derived from dolomite. The two new species strengthened the position of Mojavia as a robust genus sister to Nostoc. Although 16S rRNA gene data could not separate the Mojavia species from each other, the three species showed distinct dissimilarities in secondary ITS structure and differed greatly from Nostoc sensu stricto. The high dissimilarities between their 16S-23S ITS regions suggest a long evolutionary history of the three species as separate lineages. Mojavia is an evolutionary and ecologically unique nostocacean genus, and its rarity and restricted habitat point to an urgent need for recognition and protection.

Seed Menus: An integrated decision-support framework for native plant restoration in the Mojave Desert.

The combination of ecosystem stressors, rapid climate change, and increasing landscape-scale development has necessitated active restoration across large tracts of disturbed habitats in the arid southwestern United States. In this context, programmatic directives such as the National Seed Strategy for Rehabilitation and Restoration have increasingly emphasized improved restoration practices that promote resilient, diverse plant communities, and enhance native seed reserves. While decision-support tools have been implemented to support genetic diversity by guiding seed transfer decisions based on patterns in local adaptation, less emphasis has been placed on identifying priority seed mixes composed of native species assemblages. Well-designed seed mixes can provide foundational ecosystem services including resilience to disturbance, resistance to invasive species, plant canopy structure to facilitate natural seedling recruitment, and habitat to support wildlife and pollinator communities. Drawing from a newly developed dataset of species distribution models for priority native plant taxa in the Mojave Desert, we created a novel decision support tool by pairing spatial predictions of species habitat with a database of key species traits including life history, flowering characteristics, pollinator relationships, and propagation methods. This publicly available web application, Mojave Seed Menus, helps restoration practitioners generate customized seed mixes for native plant restoration in the Mojave Desert based on project locations. Our application forms part of an integrated Mojave Desert restoration program designed to help practitioners identify species to include in local seed mixes and nursery stock development while accounting for local adaptation by identifying appropriate seed source locations from key restoration species.

Mohave Rattlesnake (Crotalus scutulatus) Identification Revisited.

Crotalus scutulatus (Mohave rattlesnake) is a clinically significant pit viper broadly distributed across much of the arid southwestern United States and mainland Mexico. Identification of C scutulatus is a concern among emergency medical service and emergency department personnel owing to its reputation for severe envenomations and difficulty in visually differentiating between C scutulatus and other species, primarily Crotalus atrox (western diamond-backed rattlesnake). We contrast distinctive characteristics of C scutulatus, C atrox, and 3 other sympatric species: Crotalus molossus, Crotalus ornatus, and Crotalus viridis (western and eastern black-tailed rattlesnakes and prairie rattlesnake, respectively). Greenish coloration eliminates C atrox but does not confirm C scutulatus. Obvious coarse and fine speckling of the dorsal pattern and a pale postocular stripe intersecting the mouth characterize C atrox. Dorsal speckling is insignificant or absent in the other species, whereas the pale postocular stripe passes above the mouth in C scutulatus and C viridis and is absent in C molossus and C ornatus. Tails boldly ringed with alternating black and white or contrasting shades of gray are shared by C atrox and C scutulatus, respectively, but a lack of boldly ringed tails characterizes the other species. The proximal rattle segment is yellow and black, or entirely yellow, in C scutulatus but black in the others. The most reliable visual identifications are based on evaluations of multiple traits, all of which are variable to some extent. Traits such as tail ring width and the size and number of crown scales have frequently been overemphasized in the past.

Toxin tolerance across landscapes: Ecological exposure not a prerequisite.

Little is known about the tolerances of mammalian herbivores to plant specialized metabolites across landscapes.We investigated the tolerances of two species of herbivorous woodrats, Neotoma lepida (desert woodrat) and Neotoma bryanti (Bryant's woodrat) to creosote bush (Larrea tridentata), a widely distributed shrub with a highly toxic resin. Woodrats were sampled from 13 locations both with and without creosote bush across a 900 km transect in the US southwest. We tested whether these woodrat populations consume creosote bush using plant metabarcoding of feces and quantified their tolerance to creosote bush through feeding trials using chow amended with creosote resin.Toxin tolerance was analyzed in the context of population structure across collection sites with microsatellite analyses. Genetic differentiation among woodrats collected from different locations was minimal within either species. Tolerance differed substantially between the two species, with N. lepida persisting 20% longer than N. bryanti in feeding trials with creosote resin. Furthermore, in both species, tolerance to creosote resin was similar among woodrats near or within creosote bush habitat. In both species, woodrats collected greater than 25 km from creosote had markedly lower tolerances to creosote resin compared to animals from within the range of creosote bush.The results imply that mammalian herbivores are adapted to the specialized metabolites of plants in their diet, and that this tolerance can extend several kilometers outside of the range of dietary items. That is, direct ecological exposure to the specialized chemistry of particular plant species is not a prerequisite for tolerance to these compounds. These findings lay the groundwork for additional studies to investigate the genetic mechanisms underlying toxin tolerance and to identify how these mechanisms are maintained across landscape-level scales in mammalian herbivores.

The use of astronomy VLBA campaign MOJAVE for geodesy.

We investigated the suitability of the astronomical 15 GHz Very Long Baseline Array (VLBA) observing program MOJAVE-5 for estimation of geodetic parameters, such as station coordinates and Earth orientation parameters. We processed a concurrent dedicated VLBA geodesy program observed at 2.3 GHz and 8.6 GHz starting on September 2016 through July 2020 as reference dataset. We showed that the baseline length repeatability from MOJAVE-5 experiments is only a factor of 1.5 greater than from the dedicated geodetic dataset and still below 1 ppb. The wrms of the difference of estimated Earth orientation parameters with respect to the reference IERS C04 time series are a factor of 1.3 to 1.8 worse. We isolated three major differences between the datasets in terms of their possible impact on the geodetic results, i.e. the scheduling approach, treatment of the ionospheric delay, and selection of target radio sources. We showed that the major factor causing discrepancies in the estimated geodetic parameters is the different scheduling approach of the datasets. We conclude that systematic errors in MOJAVE-5 dataset are low enough for these data to be used as an excellent testbed for further investigations on the radio source structure effects in geodesy and astrometry.

Life-history strategy and extinction risk in the warm desert perennial spring ephemeral Astragalus holmgreniorum (Fabaceae).

This study of Astragalus holmgreniorum examines its adaptations to the warm desert environment and whether these adaptations will enable it to persist. Its spring ephemeral hemicryptophyte life-history strategy is unusual in warm deserts. We used data from a 22-year demographic study supplemented with reproductive output, seed bank, and germinant survival studies to examine the population dynamics of this species using discrete-time stochastic matrix modeling. The model showed that A. holmgreniorum is likely to persist in the warm desert in spite of high dormant-season mortality. It relies on a stochastically varying environment with high inter-annual variation in precipitation for persistence, but without a long-lived seed bank, environmental stochasticity confers no advantage. Episodic high reproductive output and frequent seedling recruitment along with a persistent seed bank are adaptations that facilitate its survival. These adaptations place its life-history strategy further along the spectrum from "slower" to "faster" relative to other perennial spring ephemerals. The extinction risk for small populations is relatively high even though mean λ s > 1 because of the high variance in year quality. This risk is also strongly dependent on seed bank starting values, creating a moving window of extinction risk that varies with population size through time. Astragalus holmgreniorum life-history strategy combines the perennial spring ephemeral life form with features more characteristic of desert annuals. These adaptations permit persistence in the warm desert environment. A promising conclusion is that new populations of this endangered species can likely be established through direct seeding.

Long-term nitrogen isotope dynamics in Encelia farinosa reflect plant demographics and climate.

While plant δ15 N values have been applied to understand nitrogen (N) dynamics, uncertainties regarding intraspecific and temporal variability currently limit their application. We used a 28 yr record of δ15 N values from two Mojave Desert populations of Encelia farinosa to clarify sources of population-level variability. We leveraged > 3500 foliar δ15 N observations collected alongside structural, physiological, and climatic data to identify plant and environmental contributors to δ15 N values. Additional sampling of soils, roots, stems, and leaves enabled assessment of the distribution of soil N content and δ15 N, intra-plant fractionations, and relationships between soil and plant δ15 N values. We observed extensive within-population variability in foliar δ15 N values and found plant age and foliar %N to be the strongest predictors of individual δ15 N values. There were consistent differences between root, stem, and leaf δ15 N values (spanning c. 3‰), but plant and bulk soil δ15 N values were unrelated. Plant-level variables played a strong role in influencing foliar δ15 N values, and interannual relationships between climate and δ15 N values were counter to previously recognized spatial patterns. This long-term record provides insights regarding the interpretation of δ15 N values that were not available from previous large-scale syntheses, broadly enabling more effective application of foliar δ15 N values.

ASSESSMENT OF DISEASE RISK ASSOCIATED WITH POTENTIAL REMOVAL OF ANTHROPOGENIC BARRIERS TO MOJAVE DESERT TORTOISE (GOPHERUS AGASSIZII) POPULATION CONNECTIVITY.

The Mojave Desert tortoise (Gopherus agassizii), federally listed as threatened, has suffered habitat loss and fragmentation due to human activities. Upper respiratory tract disease (URTD), a documented health threat to desert tortoises, has been detected at the Large-Scale Translocation Study Site (LSTS) in southwestern Nevada, US, a fenced recipient site for translocated animals. Our study aimed to 1) estimate prevalence of URTD and Mycoplasma infection at LSTS and three nearby unfenced sites; 2) assess whether Mycoplasma infection status was associated with developing clinical signs of URTD; and 3) determine whether such an association differed between LSTS and unfenced areas. We sampled 421 tortoises in 2016 to describe the current status of these populations. We evaluated three clinical signs of URTD (nasal discharge, ocular discharge, nasal erosions) and determined individual infection status for Mycoplasma agassizii and Mycoplasma testudineum by quantitative PCR and enzyme-linked immunosorbent assay. In 2016, LSTS had the highest prevalence of M. agassizii (25.0%; 33/132), M. testudineum (3.0%; 4/132), and URTD clinical signs (18.9%; 25/132). Controlling for other factors, clinical sign(s) were positively associated with M. agassizii infection (odds ratio [OR]=7.7, P=0.001), and this effect was similar among study sites (P>0.99). There was no association with M. testudineum status (P=0.360). Of the 196 tortoises in a longitudinal comparison of 2011-14 with 2016, an estimated 3.2% converted from M. agassizii-negative to positive during the study period, and incidence was greater at LSTS (P=0.002). Conversion to positive M. agassizii status was associated with increased incidence of clinical signs in subsequent years (OR=11.1, P=0.018). While M. agassizii and URTD are present outside the LSTS, there is a possibility that incidence of Mycoplasma infection and URTD would increase outside LSTS if these populations were to reconnect. Population-level significance of this risk appears low, and any risk must be evaluated against the potential long-term benefits to population viability through increased connectivity.

Microhabitats associated with solar energy development alter demography of two desert annuals.

Political and economic initiatives intended to increase energy production while reducing carbon emissions are driving demand for solar energy. Consequently, desert regions are now targeted for development of large-scale photovoltaic solar energy facilities. Where vegetation communities are left intact or restored within facilities, ground-mounted infrastructure may have negative impacts on desert-adapted plants because it creates novel rainfall runoff and shade conditions. We used experimental solar arrays in the Mojave Desert to test how these altered conditions affect population dynamics for a closely related pair of native annual plants: rare Eriophyllum mohavense and common E. wallacei. We estimated aboveground demographic rates (seedling emergence, survivorship, and fecundity) over 7 yr and used seed bank survival rates from a concurrent study to build matrix models of population growth in three experimental microhabitats. In drier years, shade tended to reduce survival of the common species, but increase survival of the rare species. In a wet year, runoff from panels tended to increase seed output for both species. Population growth projections from microhabitat-specific matrix models showed stronger effects of microhabitat under wetter conditions, and relatively little effect under dry conditions (lack of rainfall was an overwhelming constraint). Performance patterns across microhabitats in the wettest year differed between rare and common species. Projected growth of E. mohavense was substantially reduced in shade, mediated by negative effects on aboveground demographic rates. Hence, the rare species were more susceptible to negative effects of panel infrastructure in wet years that are critical to seed bank replenishment. Our results suggest that altered shade and water runoff regimes associated with energy infrastructure will have differential effects on demographic transitions across annual species and drive population-level processes that determine local abundance, resilience, and persistence.

Trichotorquatus gen. nov. - a new genus of soil cyanobacteria discovered from American drylands1.

Cyanobacteria are crucial ecosystem components in dryland soils. Advances in describing α-level taxonomy are needed to understand what drives their abundance and distribution. We describe Trichotorquatus gen. nov. (Oculatellaceae, Synechococcales, Cyanobacteria) based on four new species isolated from dryland soils including the coastal sage scrub near San Diego, California (USA), the Mojave and Colorado Deserts with sites at Joshua Tree National Park and Mojave National Preserve, California (USA), and the Atacama Desert (Chile). The genus is morphologically characterized by having thin trichomes (<4.5 µm wide), cells both shorter and longer than wide, rarely occurring single and double false branching, necridia appearing singly or in rows, and sheaths with a distinctive collar-like fraying and widening mid-filament, the feature for which the genus is named. The genus is morphologically nearly identical with Leptolyngbya sensu stricto but is phylogenetically quite distant from that genus. It is consequently a cryptic genus that will likely be differentiated in future studies based on 16S rRNA sequence data. The type species, T. maritimus sp. nov. is morphologically distinct from the other three species, T. coquimbo sp. nov., T. andrei sp. nov. and T. ladouxae sp. nov. However, these latter three species are morphologically very close and are considered by the authors to be cryptic species. All species are separated phylogenetically based on sequence of the 16S-23S ITS region. Three distinct ribosomal operons were recovered from the genus, lending difficulty to recognizing further diversity in this morphologically cryptic genus.

Natural ultraviolet radiation exposure alters photosynthetic biology and improves recovery from desiccation in a desert moss.

Plants in dryland ecosystems experience extreme daily and seasonal fluctuations in light, temperature, and water availability. We used an in situ field experiment to uncover the effects of natural and reduced levels of ultraviolet radiation (UV) on maximum PSII quantum efficiency (Fv/Fm), relative abundance of photosynthetic pigments and antioxidants, and the transcriptome in the desiccation-tolerant desert moss Syntrichia caninervis. We tested the hypotheses that: (i) S. caninervis plants undergo sustained thermal quenching of light [non-photochemical quenching (NPQ)] while desiccated and after rehydration; (ii) a reduction of UV will result in improved recovery of Fv/Fm; but (iii) 1 year of UV removal will de-harden plants and increase vulnerability to UV damage, indicated by a reduction in Fv/Fm. All field-collected plants had extremely low Fv/Fm after initial rehydration but recovered over 8 d in lab-simulated winter conditions. UV-filtered plants had lower Fv/Fm during recovery, higher concentrations of photoprotective pigments and antioxidants such as zeaxanthin and tocopherols, and lower concentrations of neoxanthin and Chl b than plants exposed to near natural UV levels. Field-grown S. caninervis underwent sustained NPQ that took days to relax and for efficient photosynthesis to resume. Reduction of solar UV radiation adversely affected recovery of Fv/Fm following rehydration.

Interactions among intrinsic water-use efficiency and climate influence growth and flowering in a common desert shrub.

Plants make leaf-level trade-offs between photosynthetic carbon assimilation and water loss, and the optimal balance between the two is dependent, in part, on water availability. "Conservative" water-use strategies, in which minimizing water loss is prioritized over assimilating carbon, tend to be favored in arid environments, while "aggressive" water-use strategies, in which carbon assimilation is prioritized over water conservation, are often favored in mesic environments. When derived from foliar carbon isotope ratios, intrinsic water-use efficiency (iWUE) serves as a seasonally integrated indicator of the balance of carbon assimilation to water loss at the leaf level. Here, we used a multi-decadal record of annual iWUE, growth, and flowering from a single population of Encelia farinosa in the Mojave Desert to evaluate the effect of iWUE on plant performance across interannual fluctuations in water availability. We identified substantial variability in iWUE among individuals and found that iWUE interacted with water availability to significantly influence growth and flowering. However, the relationships between iWUE, water availability, and plant performance did not universally suggest that "conservative" water-use strategies were advantageous in dry years or that "aggressive" strategies were advantageous in wet years. iWUE was positively related to the odds of growth regardless of water availability and to the odds of flowering in dry years, but negatively related to growth rates in dry years. In addition, we found that leaf nitrogen content affected interannual plant performance and that an individual's iWUE plasticity in response to fluctuations in aridity was negatively related to early life drought survival and growth.