Squirreltail Research Articles

Local adaptation to precipitation in the perennial grass Elymus elymoides: Trade-offs between growth and drought resistance traits.

Understanding local adaptation to climate is critical for managing ecosystems in the face of climate change. While there have been many provenance studies in trees, less is known about local adaptation in herbaceous species, including the perennial grasses that dominate arid and semiarid rangeland ecosystems. We used a common garden study to quantify variation in growth and drought resistance traits in 99 populations of Elymus elymoides from a broad geographic and climatic range in the western United States. Ecotypes from drier sites produced less biomass and smaller seeds, and had traits associated with greater drought resistance: small leaves with low osmotic potential and high integrated water use efficiency (δ13C). Seasonality also influenced plant traits. Plants from regions with relatively warm, wet summers had large seeds, large leaves, and low δ13C. Irrespective of climate, we also observed trade‐offs between biomass production and drought resistance traits. Together, these results suggest that much of the phenotypic variation among E. elymoides ecotypes represents local adaptation to differences in the amount and timing of water availability. In addition, ecotypes that grow rapidly may be less able to persist under dry conditions. Land managers may be able to use this variation to improve restoration success by seeding ecotypes with multiple drought resistance traits in areas with lower precipitation. The future success of this common rangeland species will likely depend on the use of tools such as seed transfer zones to match local variation in growth and drought resistance to predicted climatic conditions.

Identification of starch granules from oak and grass species in the central coast of California

Starch granule analysis is commonly used to describe the incorporation of plants into past human diets. However, assigning starch granules to particular plant taxa can be problematic. Here we take a statistical approach to analyzing multiple diagnostic characteristics of starch granules from three species of oak, Quercus agrifolia (coast live oak), Q. douglasii (blue oak), Q. lobata (valley oak) and one species of wild rye (Elymus elymoides) that were collected and consumed by hunter-gatherers in California. Results show significant differences in maximum length and the presence of morphological features (e.g., lamellae, extinction cross, mesial longitudinal clefts, fissures, shape, hilum position, etc.), suggesting that taxonomic assignment of archaeological starch granules can be made with measurable degrees of confidence.

Checklist of vascular plants for Wind River Indian Reservation (USA) high-elevation basins: ecological drivers of community assemblages

Background and aims – Native American reservations in the United States provide biodiversity critical for conservation and ecosystem functions. Unfortunately, botanical inventories are less common for reservations than other land jurisdictions. Such ecological importance and needs are apparent for the Wind River Indian Reservation (WRIR), the 7th largest reservation in the US (>890,000 ha) that is shared by the Eastern Shoshone and Northern Arapaho.Material and methods – A botanical study for two WRIR high-elevation basins (Saint Lawrence Basin (SLB) and Paradise Basin (PB)) to (1) reconcile a 1960 plant list, and (2) quantify plant communities ecologically was conducted. In 2017, 106 monitoring sites were established to quantify species presence. Across basins, 231 total vascular plant taxa (221 to species and 10 to genus) were identified, or > 3× more plant species than noted in the 1960 list. In SLB, 222 plant taxa (213 to species and 9 to genus) were identified and in PB 98 plant taxa (90 to species and 8 to genus) were identified. In 2018, sites were re-sampled to quantify species abundance, soil pH, organic matter, soil nutrients, CEC, salts, and texture. Key results – Slope and elevation explained species distributions in the topography ordination and soil organic matter, pH, texture, P, and K explained species distributions in the soil ordination. Eleven exotic species, and one rare endemic species were documented with implications for empowering tribal management. Using a classification approach followed by an indicator species analysis and fidelity (Phi) assessment, we identified 14 unique plant communities and related these to 6 alliances and 7 associations across 6 macrogroups from the US National Vegetation Classification database. These indicator species of communities included sedges (Carex aquatilus), grasses (Pseudoroegneria spicata, Elymus elymoides, Achnatherum lettermanii, Elymus trachycaulus subsp. trachycaulus, Poa glauca subsp. rupicola), forbs (Polygonum bistortoides, Balsamorhiza incana, Castilleja flava), shrubs (Artemisia tridentata, Betula glandulosa, Dasiphora fruticosa subsp. floribunda) and trees (Pinus contorta).Conclusion – The plant taxa, plant communities, and ecological drivers documented in this study will enhance tribal and federal monitoring of these high-elevation WRIR basins.

Variation in number of root tips influences survival in competition with an invasive grass

Roots are the first line for interactions between plants and the soil environment. Understanding root traits has important implications for species used in arid land restoration. Intraspecific root trait variation can have important competitive and performance ramifications that can impact the ability of a population to establish. So, we tested whether populations exhibit variation in number of root tips and whether root tip variation leads to differential interaction outcomes. We grew seedlings of eight Elymus elymoides populations from the western United States in vitro, and selected two populations with contrasting number of root tips for a greenhouse competition study with an invasive annual grass (Bromus tectorum) to assess whether differences in number of root tips affected Elymus elymoides seedling performance under competition. We found significant variation in number of root tips by population and the population with the greatest number of root tips (x̄ = 16.3 ± 8.9) had a higher proportion of individuals survive longer in competition with Bromustectorum than the population with fewer root tips (x̄ = 7.5 ± 3.1). These results highlight the need for research on intraspecific trait variation in roots for species commonly used in restoration projects to help guide the selection of appropriate source material in dry environments.

The role of soil as a carbon sink in coastal salt-marsh and agropastoral systems at La Pletera, NE Spain

To evaluate the potential of natural and modified salt-marsh soils to store organic carbon and their soil properties, we investigated six soil environments located at La Pletera salt-marsh area, NE Spain. Namely, Ruderal (RU), rubbles over marsh for construction purpose, ELY covered by Elymus elymoides (Raf.) meadows, ART under Arthrocnemum fruticosum L., SAL under Salicornia patula Duval Jouve, AGR under Zea mays L., and AME under Medicago sativa L. as artificial meadow. Soils were sampled at three depths (0–5, 5–20 and 20–40 cm). At 0–5 cm depth, soil organic carbon (SOC) was higher in ART soil (40.08 g kg−1) with respect to ELY, AME, AGR, SAL and RU (23.63, 11.45, 5.77, 4.40 and 3.18 g kg−1 respectively). Glomalin (TGRSP) in ART had the same trend, with 8.88 g kg−1 decreased by 51%, 77%, 89%, 92% and 94% in ELY, AME, AGR, SAL and RU soil respectively, indicating that in ART recalcitrant organic carbon may prevail. ART and ELY soils had higher SOC and GRSP than AGR and AME soils at 0–5 and 5–20 cm (on average + 70% and 57%) but SOC values were similar at 20–40 cm depth and glomalin was even higher in AGR and AME soils at this depth suggesting migration of stable organic compounds in cultivated soils. The water stable aggregates (WSA) analysed in the 0.25–2 mm and 2–5.6 mm fractions was also higher in ART and ELY soils (≈90%) at 0–5 and 5–20 cm with respect to the other investigated soils. Higher WSA (fraction 0.25–5 mm) was found in AGR and AME soils at 20–40 cm corroborating that at higher GRSP corresponds higher aggregation. Potential carbon loss as C-CO2 (Mg ha−1) was evaluated at 0–5 cm depth and was much lower in ART soil. Accordingly, C-CO2/SOC ratio assigned to ART soil 1.85% of SOC loss against 8.26%, 11.64%, 18.90%, 20.37% and 22.72% of ELY, AME, RU, SAL and AGR soils respectively, indicating that only ART and ELY soils may exert clear carbon sequestration ability. The soil under annual Salicornia patula Duval Jouve (SAL) showed very low SOC (4.40 g kg−1) and the highest carbon loss potential (22.72%) due to shortage of organic decaying debris at surface. Also, C-TGRSP resulted higher in ELY and ART soils (2.51 and 1.31 Mg ha-1respectively) and C-TGRSP/SOC ratio demonstrated glomalin carbon enrichment in this order: ART > AME > ELY > AGR > SAL > RU, suggesting that carbon sequestration capacity may be assigned to ART and ELY soils, major carbon sinks in the Pletera salt-marsh area. Conversely, RU, AGR and AME soils, identified as ancient salt-marsh converted into agropastoral systems or altered for tourism purposes showed worse soil properties and higher sensitivity to carbon destabilization. Statistical treatment of data by factor analysis corroborated the obtained results outlining the importance of ART and ELY soils in maintaining best soil properties and the highest carbon storage capacity.

Biocrusts are associated with increased plant biomass and nutrition at seedling stage independently of root-associated fungal colonization

Plant-soil interactions are important drivers of plant productivity and community structure. Biocrusts – soil surface-dwelling biotic communities comprised of cyanobacteria, fungi, bryophytes, and/or lichens - are widespread in drylands globally. Biocrusts are described as “mantles of fertility” and have been shown to have facilitative, but species-specific effects on plant productivity. Yet, patterns and mechanisms underlying biocrust facilitation of plant productivity remain unclear. Using mesocosms with bare soil versus biocrust cover we investigated the effects of biocrusts on plant biomass allocation, leaf chemistry and colonization by root-associated fungi. Plant responses to biocrust presence were species-specific. Overall, biocrusts were associated with increased plant biomass and/or leaf N concentrations in Elymus elymoides, Bouteloua gracilis and Zea mays. However, plants grown in biocrusts had lower root-associated fungal colonization compared to bare soils. Biocrusts were associated with increased plant biomass and leaf N. Yet, plant growth responses to biocrusts were not correlated with differences in root-associated fungal colonization between soil mesocosm types. Understanding species-specificity in biocrust facilitation of plant growth may have important implications for understanding plant community structure in dryland ecosystems.

Seed head photosynthetic light responses in clipped and unclipped sagebrush steppe bunchgrasses

Low seedling establishment limits the long-term success of sagebrush steppe restoration, and the physiological mechanisms underlying this remain unclear. To address this, we measured the photosynthetic light responses and seed head specific length (mg cm−1) of shaded and unshaded seed heads in clipped and unclipped plants to determine if grazing affects reproductive photosynthesis in sagebrush steppe bunchgrasses. We measured responses in an exotic species, Agropyron cristatum (crested wheatgrass) that readily establishes from seed, and two native grasses, Elymus elymoides (squirreltail wild rye) and Psuedororegnaria spicata (bluebunch wheatgrass), which do not. Defoliation did not affect seed head light saturation responses in any of the grasses. Agropyron cristatum seed heads attained higher light-saturated photosynthesis and higher photosynthetic light use efficiencies than the native grasses, consistent with its ability to produce viable seed crops. Defoliation and shading reduced post-anthesis seed head specific masses only in E. elymoides, suggesting this species reproductive effort relies on carbon fixed by the seed head itself. These findings could help in the selection and development of native plant materials with characteristics similar to the successful exotic grass to improve restoration efforts in degraded sagebrush steppe ecosystems.

The role of inoculum dispersal and plant species identity in the assembly of leaf endophytic fungal communities.

Because of disturbance and plant species loss at the local level, many arid ecosystems in the western USA benefit from revegetation. There is a growing interest in improving revegetation success by purposefully inoculating revegetation plants with mutualistic endophytic fungi that increase plant stress tolerance. However, inoculant fungi must compete against fungi that indigenous to the habitat, many of which may not be mutualistic. Our overall goal, therefore, is to learn how to efficiently colonize revegetation plants using endophytic fungal inoculum. The goal will be facilitated by understanding the factors that limit colonization of plants by endophytic fungi, including inoculum dispersal and host compatibility. We analyzed endophytic fungal communities in leaves of Bromus tectorum and Elymus elymoides (Poaceae), Chrysothamnus depressus and Artemisia tridentata (Asteraceae), Alyssum alyssoides (Brassicaceae) and Atriplex canescens (Amaranthaceae), each occurring in each of 18 field plots. We found that dispersal limitation was significant for endophytic fungal communities of Atriplex canescens and Bromus tectorum, accounting for 9 and 17%, respectively, of the variation in endophytic fungal community structure, even though the maximum distance between plots was only 350 m. Plant species identity accounted for 33% of the variation in endophytic fungal community structure. These results indicate that the communities of endophytic fungi assembling in these plant species depend significantly on proximity to inoculum source as well as the identity of the plant species. Therefore, if endophytic fungi are to be used to facilitate revegetation by these plant species, land managers may find it profitable to consider both the proximity of inoculum to revegetation plants and the suitability of the inoculum to targeted host plant species.

Characterization of Adult Functional Traits of Local Populations and Cultivars of Sandberg Bluegrass and Bottlebrush Squirreltail Perennial Bunchgrasses.

Plant functional traits offer an understanding of the plant’s ability to cope with varying environmental impositions. The objective of this study was to evaluate the above and belowground adult morphological and chemical composition traits of local populations of Sandberg bluegrass (Poa secunda J. Presl) and Bottlebrush squirreltail (Elymus elymoides (Raf.) Swezey) collected in Nevada and their cultivated varieties. A total of six replications (one seedling each) from each population and cultivar of the two native perennial bunchgrasses were used in a randomized complete block design experiment. Each of the six seedlings from each sourced population was transplanted into individual tree pots (28 cm diameter × 61 cm height) containing 20.4 kg of air-dried Orr gravelly sandy loam soil in mid-November, 2015 and remained in the pots for the duration of the study (23 June, 2016). Traits evaluated were, plant height, leaf length, inflorescence length, shoot biomass, forage nutritive value, root morphological traits, and root carbon and nitrogen content. Traits means were considered different at P < 0.05. For Sandberg bluegrass, the cultivar ‘Mountain Home’ and the population from Panther Valley tended to have greater biomass than the population from Button Point but overall, the average of the two cultivars (10.8 g/plant) did not differ in shoot biomass relative to the local populations (7.6 g/plant). For squirreltail, plant height for the George St. Sonoma and Grass Valley populations (71.3 cm) was greater than the cultivars ‘Toe Jam Creek’ and ‘Vale’ (40.5 cm) but cultivars had greater biomass (12.6 g/plant) than the local populations (5.8 g/plant). Total root length and root diameter were not different among the Sanberg bluegrass and squirreltail populations. The results from traits expounded on in this study indicate the closeness of these populations for both species at their adult stage and provide insights for building a unified framework approach among the different agencies and restoration practitioners to aid in plant assemblages for restoration success in the Great Basin and beyond.

Solarization to control downy brome (Bromus tectorum) for small-scale ecological restoration

AbstractDowny brome (Bromus tectorum L.) is a common impediment to ecological restoration, because its seedbank remains viable after repeated treatment with herbicides. Soil solarization has been used in ecological restoration to control seedbanks of invasive plants. Here we test the efficacy of soil solarization to reduce B. tectorum cover and establish native plants at a site in B. tectorum’s core invasive range with a long history of disturbance and infestation. Solarization raised soil temperatures by as much as 13 C and reduced B. tectorum densities by approximately 20-fold. In 30 plots solarized for 0 to 101 d, B. tectorum emerged in inverse abundance to treatment duration. Broadleaf weeds were less abundant than B. tectorum before treatment, and diminished under solarization, but their response to solarization was weaker than B. tectorum’s, and they emerged in greater numbers than B. tectorum 2 to 3 yr after treatment. When seeded after solarization, a native perennial bunchgrass, squirreltail [Elymus elymoides (Raf.) Swezey], did not differ in abundance between solarized and control plots. Solarization may facilitate B. tectorum control on a small scale without jeopardizing the establishment of native plants, but only if treatment durations are long and subsequent management of broadleaf weeds and remnant B. tectorum is planned.

Seed and seedling traits have strong impacts on establishment of a perennial bunchgrass in invaded semi‐arid systems

Abstract Many restoration projects use seeds to found new populations, and understanding phenotypic traits associated with seedling establishment in disturbed and invaded communities is important for restoration efforts world‐wide. Focusing on the perennial grass Elymus elymoides, a native species common to sagebrush steppe communities in the Western United States, we asked if seed and seedling traits could predict field establishment. We collected seeds from 34 populations from the western Great Basin. In greenhouse studies, we measured variation in seed and seedling characteristics of wild populations and one cultivar. We also quantified abiotic conditions at the collection location and asked if these characteristics predicted survival and other fitness metrics at five planting sites. Planting sites were all near‐monocultures of the invasive annual grass Bromus tectorum, and all sites experienced similar, below‐average precipitation during the experiment. Phenotypic traits were strongly correlated with performance across all sites, with remarkably high predictive power. Seeds from populations with longer roots, larger seeds and earlier emergence were significantly more likely to survive the first growing season (R2 = 0.66, p &lt; 0.0001). In contrast, while some abiotic variables at the collection location (e.g. 30‐year average summer precipitation and fall minimum temperatures) were associated with field performance at some sites, abiotic variables explained less variation in performance than traits (average R2 = 0.22). Despite the low predictive power of abiotic variables, populations that performed best at each field site were from locations with climate variables similar to planting sites. Synthesis and applications. The best seed sources for restoration of Elymus elymoides in invaded sites were populations with longer roots, larger seeds and earlier emergence. These easily measured traits were strong predictors of survival in disturbed field sites. While the most successful populations were found in areas with similar abiotic conditions as planting sites, there was phenotypic variation even among populations originating from locations with similar conditions. Thus, our results indicate that abiotic conditions are important considerations when selecting seeds, but these conditions may not sufficiently predict which populations will establish. Understanding population differences in seedling functional traits can improve predictions of restoration success.

An experimental test of the Community Assembly by Trait Selection (CATS) model.

The Community Assembly by Trait Selection (CATS) model of community assembly predicts species abundances along environmental gradients in relatively undisturbed vegetation. Here we ask whether this model, when calibrated with data from natural plant communities, can predict the abundances of five dominant grass species (Bouteloua gracilis, Elymus elymoides, Festuca arizonica, Muhlenbergia montana, and Poa fendleriana) in a greenhouse experiment that manipulated light and soil properties. To address this question, we used generalized additive models (GAMs) to model community-weighted mean (CWM) seed mass, mean Julian flowering date, and specific root length (SRL) as non-linear functions of two environmental variables (soil pH and pine basal area) in natural vegetation. The model-fitted CWM traits were then used as constraints in the CATS model to predict the relative abundance of the five grass species that were seeded in a mixture at equal densities into a 2×2 factorial experiment with soil parent material and light level as crossed factors. Light was the most important factor influencing seedling community composition, especially the abundances of Bouteloua gracilis and Poa fendleriana. The model-predicted relative abundances were significantly correlated with the observed relative abundances, and the model accurately predicted the dominant species in every treatment. P. fendleriana was correctly predicted to be the most abundant species in both shade treatments and the sun-basalt treatment, and B. gracilis was correctly predicted to be the most abundant species in the sun-limestone treatment. Our results provide experimental evidence that environmental filtering of the species pool occurs in the early stages of community assembly (including germination, emergence, and early growth), and that trait-based models calibrated with data from natural plant communities can be used to predict the outcome of the early stages of community assembly under experimental conditions.

Use of auto-germ to model germination timing in the sagebrush-steppe.

Germination timing has a strong influence on direct seeding efforts, and therefore is a closely tracked demographic stage in a wide variety of wildland and agricultural settings. Predictive seed germination models, based on soil moisture and temperature data in the seed zone are an efficient method of estimating germination timing. We utilized Visual Basic for Applications (VBA) to create Auto‐Germ, which is an Excel workbook that allows a user to estimate field germination timing based on wet‐thermal accumulation models and field temperature and soil moisture data. To demonstrate the capabilities of Auto‐Germ, we calculated various germination indices and modeled germination timing for 11 different species, across 6 years, and 10 Artemisia‐steppe sites in the Great Basin of North America to identify the planting date required for 50% or more of the simulated population to germinate in spring (1 March or later), which is when conditions are predicted to be more conducive for plant establishment. Both between and within the species, germination models indicated that there was high temporal and spatial variability in the planting date required for spring germination to occur. However, some general trends were identified, with species falling roughly into three categories, where seeds could be planted on average in either fall (Artemisia tridentata ssp. wyomingensis and Leymus cinereus), early winter (Festuca idahoensis, Poa secunda, Elymus lanceolatus, Elymus elymoides, and Linum lewisii), or mid‐winter (Achillea millefolium, Elymus wawawaiensis, and Pseudoroegneria spicata) and still not run the risk of germination during winter. These predictions made through Auto‐Germ demonstrate that fall may not be an optimal time period for sowing seeds for most non‐dormant species if the desired goal is to have seeds germinate in spring.

Drought timing, not previous drought exposure, determines sensitivity of two shortgrass species to water stress.

Climate change will alter global precipitation patterns, making it increasingly important that we understand how ecosystems will be impacted by more frequent and severe droughts. Yet most drought studies examine a single, within-season drought, and we know relatively little about the impacts of multiple droughts that occur within a single growing season. This distinction is important because many plant species are able to acclimate physiologically, such that the effects of multiple droughts on ecosystem function deviate significantly from the effects of cumulative, independent droughts. Unfortunately, we know relatively little about the ability of dominant species to acclimate to drought in drought-sensitive ecosystems like semi-arid grasslands. Here, we tested for physiological acclimation to multiple drought events in two dominant shortgrasssteppe species: Bouteloua gracilis (C4) and Elymus elymoides (C3). Neither species exhibited physiological acclimation to drought; leaf water potential, stomatal conductance, and photosynthesis rates were all similarly affected by a single, late period drought and a second, late period drought. Biomass was lowest in plants exposed to two droughts, but this is likely due to the cumulative effects of both an early and late period drought. Our results suggest that late period droughts do exert weaker effects on biomass production of two dominant shortgrass species, but that the weaker effects are due to ontogenetic changes in plant physiology as opposed to physiological acclimation against multiple droughts. As a consequence, current ecosystem models that incorporate grass phenology and seasonal physiology should provide accurate predictions of primary production under future climates.

Establishment and Trends in Persistence of Selected Perennial Cool-Season Grasses in Western United States

Restoring western US rangelands from a site dominated by invasive annuals, such as cheatgrass and medusahead, to a diverse, healthy, perennial plant−dominated ecosystem can be difficult with native grasses. This study describes the establishment and trends in persistence (plant/m2) of native grass cultivars and germplasm compared with typically used crested and Siberian wheatgrasses at four locations in Idaho (one), Wyoming (one), and Utah (two) that range in mean average annual precipitation (MAP) from 290 to 415 mm. Sites were cultivated and fallowed 1 yr before planting using two glyphosate applications to control weeds. We monitored seedling establishment of 10 perennial cool-season grass species and plant persistence over 5 yr. Precipitation during the seeding year varied with the Utah sites locations reviving below MAP (4% and 14%), while the Wyoming and Idaho sites received above MAP at 8% and 26%, respectively. Across these four sites, native grass seedling establishment of bottlebrush squirreltail (29 ± 0.08 [standard error] seedling/m2), bluebunch (28 ± 0.05), slender (30 ± 0.05), and Snake River wheatgrasses (28 ± 0.08) was similar to “Vavilov II” Siberian wheatgrass (36 ± 3.20). By yr 5, western, Snake River, and thickspike wheatgrasses were the only native grasses to have plant densities similar to Vavilov II (37 ± 0.29) Siberian and “Hycrest II” (36 ± 0.29) crested wheatgrasses. On sites receiving between 290 and 415 mm MAP, our data suggest that native grasses are able to establish but in general lack the ability to persist except for western, Snake River, and thickspike wheatgrasses, which had plant densities similar to crested and Siberian wheatgrasses after 5 yr.

Granivory from native rodents and competition from an exotic invader strongly and equally limit the establishment of native grasses.

Seed predation and resource competition are fundamental biotic filters that affect the assembly of plant communities, yet empirical studies rarely assess their importance relative to one another. Here, we used rodent exclosures and experimental seed additions to compare how rodent granivory and resource competition affected the net establishment of an exotic invader (Bromus tectorum) and two native bunchgrasses (Pseudoroegneria spicata and Elymus elymoides) in the Great Basin Desert, USA. Rodent granivory limited the establishment of both native grasses, but had no significant effect on B. tectorum. Competition from B. tectorum limited the establishment of both native grasses, but neither native grass imposed a significant competitive effect on B. tectorum. Interestingly, we found that rodent granivory and B. tectorum competition limited the establishment of native grasses to the same extent, suggesting that these biotic interactions may impose equally important barriers to the local establishment of P. spicata and E. elymoides. By evaluating the strength of multiple biotic interactions in simultaneous, coordinated experiments, we can understand their relative contributions to community-level patterns.

Preestablished Plant Influences on Antelope Bitterbrush (Purshia tridentataPursh) Seedling Recruitment and Growth: Analysis of Species and Positional Effects

We evaluated the influence of preestablished plant species distance, direction, and identity on antelope bitterbrush (Purshia tridentata Pursh) seedling establishment and biomass production. Antelope bitterbrush seeds were planted 10- and 20-cm away from the base of three preestablished plant species. We monitored seedling establishment and growth during and after two growing seasons. Sowing antelope bitterbrush seeds 20-cm away from preestablished plant bases yielded 1.59 times greater seedling establishment than seeds sown 10-cm away, suggesting that established plants interfere with bitterbrush recruitment. Antelope bitterbrush seedling survival after 2 y of growth was greater than 96% for all treatments, suggesting that early growth phases were the primary bottlenecks to establishment. Antelope bitterbrush forage production decreased with proximity to preestablished plants. After 2 y of growth, antelope bitterbrush biomass was almost 3 times greater for plants grown without preestablished plant neighbors or with a preestablished grass (Elymus elymoides Raf.) than with preestablished forb species (Dalea candida Michx. ex Willd. or Gaillardia aristata Pursh). Inoculating preestablished plants with soil from native sites or arbuscular mycorrhizal fungi did not influence antelope bitterbrush establishment or growth. We suggest that plant trait complementarity and spatial relationships can be used to design seeding strategies to increase antelope bitterbrush establishment and forage production.

A spring rainfall pulse causes greater in situ photosynthetic upregulation for Bromus tectorum compared to co-occurring native herbaceous species

The invasive grass Bromus tectorum fuels fires, displaces native species, and reduces wildlife habitat on sagebrush steppe throughout the western United States. Recently, it has spread from the Great Basin Desert into higher elevations of the eastern Sierra Nevada, where it coexists with natives but has not yet altered fire regimes. We evaluated effects of a springtime water pulse (+10mm) in a drought year on photosynthesis for B. tectorum and co-occurring shallow-rooted native perennials Achnatherum hymenoides, Elymus elymoides, and Lupinus argenteus near the range limit of B. tectorum at ∼2175m in California. Watered B. tectorum had the largest increase in stomatal conductance (27%) of the four species. Watering increased CO2 assimilation for B. tectorum by 78% over controls, compared to 17% for A. hymenoides, 2% for E. elymoides, and 29% for L. argenteus. Electron transport rate within Photosystem II increased for watered B. tectorum and A. hymenoides, but not for E. elymoides and L. argenteus. Instantaneous electron transport rate and carbon assimilation were more responsive for B. tectorum than natives following a spring water pulse during drought. Rapid upregulation of carbon uptake in spring in response to soil re-wetting during drought could facilitate B. tectorum spread at high elevation.

Grazing Effects on Precipitation-Driven Associations between Sagebrush and Perennial Grasses

Abstract. While many studies have addressed the effect of individual stresses on plant—plant associations, few have addressed the effects of co-occurring stresses. We therefore investigated how associations between Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and 2 native grasses (Poa secunda and Elymus elymoides) responded to different combinations of grazing and moisture stresses in the Great Basin, USA. Positive (i.e., facilitative) interactions between nurse plants and their beneficiaries are predicted to increase with increasing moisture limitation and grazing stress, but these interactions may break down at extreme levels of stress. We hypothesized that (1) competitive interactions and negative shrub-grass spatial associations would occur under the least stressful conditions (low grazing intensity / high precipitation); (2) positive shrub-grass spatial associations would dominate at intermediate levels of stress (high grazing intensity / high precipitation and low grazing intensity...

Postdefoliation ecosystem carbon and water flux and canopy growth dynamics in sagebrush steppe bunchgrasses

AbstractDeveloping land‐use practices that lead to sustainable net primary productivity in rangelands are important, but understanding their consequences to population and community processes is not often accounted for in basic ecosystem studies. Grazed and ungrazed upland ecosystems generally do not differ in net ecosystem CO2 exchange (NEE), but the underlying mechanisms and the concurrent effects of defoliation to vegetative and reproductive biomass allocation are unclear. To address this, we measured evapotranspiration (ET), NEE, and its constituent fluxes of ecosystem respiration (Reco) and gross ecosystem photosynthesis (GEP) with live canopy leaf area index (LAIlive; m2 live leaf area/m2 ground area) and aboveground leaf, culm, and reproductive biomass in plots of clipped and unclipped squirreltail (Elymus elymoides) and bluebunch wheatgrass (Pseudoroegneria spicata) growing in intact sagebrush steppe. Clipping reduced LAIlive by 75%, but subsequent re‐growth rates in clipped plots was similar to LAIlive accumulation in unclipped plots. Concurrently, ET and NEE was similar between clipped and unclipped plots, with NEE primarily determined by GEP. GEP was initially lower in clipped plots, but then converged with unclipped GEP even as LAIlive continued to increase in both treatments. GEP convergence was driven by higher whole‐plant photosynthesis (GEPlive = GEP/LAIlive) in clipped plots. Ecosystem water use efficiency (GEP/ET) was reduced by 16% with clipping, due to low GEP/ET 2 weeks following defoliation, but GEP/ET converged before GEP levels did. Proportional reproductive biomass was higher in E. elymoides (21.4% total biomass) than in P. spicata (0.5% total biomass) due to lower allocation to specific leaf and culm mass. Clipping reduced reproductive effort in E. elymoides, in terms of total reproductive biomass (−56%), seed mass per unit leaf area (−64%), and seed mass per flowering head (−77%). We concluded defoliation increased canopy‐level light penetration, facilitating rapid recovery of ecosystem fluxes, but that allocation to vegetative regrowth supporting this led to lower reproductive effort in these range grasses. Insights from studies such as this will be useful in formulating systems‐based land management strategies aimed at maintaining annual productivity and long‐term population and community goals in semiarid rangeland ecosystems.