Western Wheatgrass Research Articles

Facilitation of an Exotic Grass Through Nitrogen Enrichment by an Exotic Legume

Invasive species control requires understanding the mechanisms behind their establishment and their interactions with other species. One potential ecosystem alteration influencing the establishment and spread of invasive species is anthropogenic nitrogen enrichment, from sources like introduced or invasive nitrogen (N)-fixing legumes, which can alter competition between native, non-native, and invasive plants. Kentucky bluegrass (Poa pratensis) and N-fixing yellow sweet clover (Melilotus officinalis) are exotic to the Great Plains and are currently invading and degrading native rangelands by altering ecosystem processes and displacing native plants. Therefore, we investigated how N enrichment from yellow sweet clover affects the aboveground biomass production of Kentucky bluegrass and western wheatgrass (Pascopyrum smithii), a native cool-season grass, the ranges of which overlap in the northern Great Plains. In a controlled greenhouse environment, we conditioned experimental pots by growing yellow sweet clover and terminating each plant after 8 wk. Conditioned soils contained ≈340% more plant-available N than untreated soils 2 wk after yellow sweet clover death. We then grew Kentucky bluegrass and western wheatgrass transplant seedlings in interspecific and intraspecific pairs in pots conditioned either with or without yellow sweet clover for 12 wk. Aboveground biomass production of both Kentucky bluegrass and western wheatgrass grown in interspecific and intraspecific pairs increased in conditioned soils. However, when grown together in conditioned pots, the increase in Kentucky bluegrass biomass relative to untreated pots (520%) was double that of the increase in western wheatgrass biomass (260%). Our results reveal that Kentucky bluegrass can use increased soil N to produce proportionally more aboveground biomass than western wheatgrass, a native grass competitor. Thus, our results suggest yellow sweet clover and other sources of N enrichment may facilitate the invasion of Kentucky bluegrass.

Testing the cultivar vigor hypothesis: comparisons of the competitive ability of wild and cultivated populations of Pascopyrum smithii along a restoration chronosequence

Restoration practitioners often rely on seeds of widely available cultivars representing native species but nonlocal germplasm. Cultivation improves the supply of plant materials and minimizes revegetation costs, but can also favor agronomic traits, and resulting vigor may affect the competitive ability and long‐term persistence of cultivated genotypes at restoration sites. We compared cultivated, restored, and wild populations of Pascopyrum smithii (western wheatgrass) in a greenhouse study to test the extent to which cultivars outcompete local plants in biomass production, and to determine if morphological differences (including height and number of leaves) among cultivated and wild populations persist at restoration sites over time. We found evidence of vigor and greater competitive ability of cultivars in seed mass, growth rate, plant height, and biomass and this advantage occurred when plants were grown alone or in competition with other seed sources. Cultivar vigor persisted at restoration sites over 30 years, but restored populations more closely resembled wild, local populations when cultivars were planted in closer proximity to nearby undisturbed sites. This study supports the cultivar vigor hypothesis and provides evidence for the long‐term persistence of cultivated traits in the environment.

Elevated CO2 induces substantial and persistent declines in forage quality irrespective of warming in mixedgrass prairie.

Increasing atmospheric [CO2 ] and temperature are expected to affect the productivity, species composition, biogeochemistry, and therefore the quantity and quality of forage available to herbivores in rangeland ecosystems. Both elevated CO2 (eCO2 ) and warming affect plant tissue chemistry through multiple direct and indirect pathways, such that the cumulative outcomes of these effects are difficult to predict. Here, we report on a 7-yr study examining effects of CO2 enrichment (to 600ppm) and infrared warming (+1.5°C day/3°C night) under realistic field conditions on forage quality and quantity in a semiarid, mixedgrass prairie. For the three dominant forage grasses, warming effects on invitro dry matter digestibility (IVDMD) and tissue [N] were detected only in certain years, varied from negative to positive, and were relatively minor. In contrast, eCO2 substantially reduced IVDMD (two most abundant grasses) and [N] (all three dominant grass species) in most years, except the two wettest years. Furthermore, eCO2 reduced IVDMD and [N] independent of warming effects. Reduced IVDMD with eCO2 was related both to reduced [N] and increased acid detergent fiber (ADF) content of grass tissues. For the six most abundant forage species (representing 96% of total forage production), combined warming and eCO2 increased forage production by 38% and reduced forage [N] by 13% relative to ambient climate. Although the absolute magnitude of the decline in IVDMD and [N] due to combined warming and eCO2 may seem small (e.g., from 63.3 to 61.1% IVDMD and 1.25 to 1.04% [N] for Pascopyrum smithii), such shifts could have substantial consequences for the rate at which ruminants gain weight during the primary growing season in the largest remaining rangeland ecosystem in North America. With forage production increases, declining forage quality could potentially be mitigated by adaptively increasing stocking rates, and through management such as prescribed burning, fertilization at low rates, and legume interseeding to enhance forage quality.

Low-maintenance turfgrass potential of crested, thickspike and western wheatgrass germplasm

Traditional cool-season turfgrass species, such as Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), and tall fescue (Lolium arundinaceum [Schreb.] Darbysh.), provide high quality turfgrass for athletic and aesthetic uses. Unfortunately, this high level of quality often comes at a cost of high levels of inputs in the forms of irrigation and fertilization. Therefore, there is a growing need and demand to produce turfgrass with lower inputs, particularly irrigation. Herein, we describe a study of the turfgrass potential of crested wheatgrass (Agropyron cristatum [L.] Gaertn.), thickspike wheatgrass (Elymus lanceolatus [Scribn. & J.G. Sm.] Gould) and western wheatgrass (Pascopyrum smithii [Rydb.] A. Love) when managed under low irrigation. We found that these species generally exhibited lower percent ground cover than tall fescue and Kentucky bluegrass under reduced irrigation, but that they exhibited darker green color. We identified a large range of phenotypic values and generally high narrow sense heritability (h2>0.5) for turf quality within these species, particularly for thickspike and western wheatgrass. Selection for increased turfgrass quality in these wheatgrass species has a high likelihood of developing improved turfgrass cultivar in these species.

Interseeding Warm-Season Annual Grasses into Perennial Cool-Season Western Wheatgrass Pasture

Interseeding Warm-Season Annual Grasses into Perennial Cool-Season Western Wheatgrass Pasture

Mixtures of native perennial forage species produce higher yields than monocultures in a long-term study

To evaluate the forage yield and quality of seven perennial native species in monoculture and binary mixtures under a range of climate conditions, a 6-yr field experiment was conducted at the Swift Current Research and Development Centre (SCRDC), Agriculture and Agri-Food Canada (AAFC), in Swift Current, SK. Seven native perennial forage species from three functional groups (C3, C4grasses, and legumes) were seeded in 2010 in monocultures and binary mixtures. Forage yield and quality [crude protein, acid detergent fiber (ADF), neutral detergent fiber (NDF), phosphorus (P), calcium (Ca), and copper (Cu)] were measured during the first week of July and last week of August in 2011–2016. Mixtures that included western wheatgrass [Pascopyrum smithii (Rydb.) Löve] (WWG) tended to produce a greater yield when 90% of the composition within these mixtures was WWG. Adding bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Löve] (BBW), little blue stem [Schizachyrium scoparium (Michx.) Nash] (LBS), and prairie clovers (Dalea spp.) to the binary mixtures can increase the positive aspects of species diversity on stability and productivity in seeded pastures. Among the grasses, WWG contained higher crude protein and lower ADF and NDF concentration. Mixtures of forage species produced higher forage yield compared with monocultures. Native forage species can produce stable forage yield across very different climate situations. In mixtures, WWG showed promising results in forage productivity and quality and can be a suitable option for seeded pastures.

Divergent effects of defoliation intensity and frequency on tiller growth and production dynamics ofPascopyrum smithiiandHesperostipa comata

Rotational stocking theoretically enables regrazing of regrowth, but regrowth may be limited in xerophytic vegetation. We tested the hypothesis that regrowth would be slow and fixed in Hesperostipa comata (a caespitose, drought-tolerant grass), while growth would be flexible in Pascopyrum smithii (a rhizomatous, less drought-tolerant grass) under increasing defoliation and moisture, by assessing tiller growth rates, population dynamics and plant yield on marked plants in a Dry Mixed Grass prairie. Plots were clipped in late summer to simulate a deferred control, or intermittently during the growing season (May–August) at high intensity–low frequency (HILF), low intensity–high frequency (LIHF) or high intensity–high frequency and crossed with two water treatments (ambient and addition) in both a xeric upland and a mesic lowland. Growing season defoliation increased tiller growth rates of P. smithii in the upland, whereas HILF and LIHF reduced growth in the lowland. All defoliation regimes increased tiller growth for H. comata. Tiller populations of H. comata increased with frequent defoliation, while tiller populations of P. smithii decreased regardless of defoliation regime. Frequent defoliation, regardless of intensity, reduced yield relative to the deferred control for both grasses. While water addition consistently increased growth rates and reduced differences in tiller number among defoliation treatments, the regrowth of both grasses remained similar under varied defoliation with ambient moisture. High moisture conditions also promoted regrowth more in P. smithii compared to H. comata. In summary, neither grass species displayed an inherently fixed or flexible tiller or plant yield response in response to defoliation or moisture.

The potential of seven native North American forage species to suppress weeds through allelopathy

We conducted a series of three greenhouse studies to study the allelopathic effects of seven native perennial North American forage species alone and mixed on three problematic weeds including dand...

Digging into the roots of belowground carbon cycling following seven years of Prairie Heating and CO2 Enrichment (PHACE), Wyoming USA

Grassland soils are significant carbon (C) sinks as more than half of grassland plant biomass is belowground and roots are the main source of soil C. It is uncertain if grassland soils will continue as C sinks in the future because climate change may affect the dynamic, belowground relationships among crown and root biomass, root chemistry and morphology, and root and soil decomposition, all of which influence C sequestration potential. To better understand future belowground C cycling in semiarid grasslands we analyzed three native species (Bouteloua gracilis, Carex eleocharis, and Pascopyrum smithii) and mixed-grass community crown and root biomass, root chemistry, morphology, and decomposability, and soil organic carbon (SOC) priming following seven years of simulated climate change at the Prairie Heating and CO2 Enrichment (PHACE) experiment in Wyoming, USA. We found that individual species and the community respond uniquely to the climate change field treatments, indicating that species composition is important when analyzing climate change effects on grassland C cycling. Root biomass in the C3 sedge, C. eleocharis, increased under elevated CO2, especially when combined with warming. Decomposition rates of roots from warming plots were higher than those from ambient plots for B. gracilis and P. smithii. Across species, root decomposition rates increased with C and N concentrations. Root morphology was altered as well: B. gracilis root diameter increased under warming, and P. smithii specific root length and surface area increased under elevated CO2. P. smthii roots induced short-term, negative SOC priming across all field treatments. Together, our results indicate that grass roots may play a critical role in maintaining soil C stocks in grasslands in the future.

Phenology of perennial, native grass, belowground axillary buds in the northern mixed-grass prairie.

Vegetative reproduction from belowground bud banks is the primary driver of grassland systems. Despite the importance of bud banks, the timing of recruitment and the crucial link between formation and maintenance is unknown. We assessed patterns of belowground bud development, dormancy, and mortality associated with three perennial native grasses in the northern Great Plains. Temperature and soil moisture were measured below the soil surface to determine relationships with belowground bud development. Blue grama (Bouteloua gracilis) generated more buds over winter that remained dormant; whereas, C3 species needle-and-thread (Hesperostipa comata) and western wheatgrass (Pascopyrum smithii), maintained limited dormant buds throughout winter. Soil temperature was a good predictor for C4 species bud production; whereas, soil moisture was a reliable predictor for C3 buds. Distinct differences existed between C4 species blue grama and C3 species needle-and-thread, whereas C3 species western wheatgrass (Pascopyrum smithii) was intermediate, indicating there is likely a species-specific continuum between the C3 and C4 extremes rather than a stark difference. The ability to predict belowground bud development is a novel insight to native perennial grasses. Native grass species' strategies and adaptability regarding belowground bud bank size and bud phenology are important factors optimizing tiller recruitment given the variable growing conditions. Patterns of bud dormancy and development will provide insight to the underlying mechanisms by which management practices and fluctuations in precipitation amount and growing season length can alter mixed-grass prairie plant community dynamics.

Grazing moderates increases in C3 grass abundance over seven decades across a soil texture gradient in shortgrass steppe

AbstractQuestionsHow does long‐term exclusion of cattle grazing influence plant community composition in a semi‐arid grassland? Can spatial variation in the effects of cattle grazing exclusion be explained by variation in soil texture?LocationShortgrass steppe, northeast Colorado, USA, in the North American Great Plains.MethodWe used 16 long‐term (72 yr) cattle exclosures to examine the effects of grazers on plant communities and evaluate whether grazer effects interact with soil texture.ResultsAlthough shortgrass steppe communities are relatively unaffected by grazing in the short‐term (one to two decades), exclusion of cattle grazing for seven decades caused a compositional shift from dominance by a C4 shortgrass (Bouteloua gracilis) to co‐dominance by a C3 midgrass (Pascopyrum smithii) and B. gracilis. The strength of this shift was highly variable across sites. Soil texture was correlated with the abundance of certain plant species, but did not explain variation in the magnitude of grazer effects. Grazed communities contained perennial and annual growth forms with a diversity of strategies to co‐exist with grazers and B. gracilis. Ungrazed communities included increased abundance of annual, ruderal forbs and three woody plant species. Grazing effects occurred against a backdrop of changing plant communities: during the past seven decades, C3 perennial graminoids and sub‐shrubs have increased in relative abundance in both grazed and ungrazed communities.ConclusionsOur long‐term experiment shows that community responses to grazing in this semi‐arid grassland occur very slowly, but are predictable, with C4 shortgrasses eventually giving way to taller C3 grasses and ruderal forbs. Spatial variation in grazing effects across sites (and lack of a relationship with soil texture) may reflect the importance of fine‐scale heterogeneity in C3 grass abundance, and the slow rate at which taller C3 grasses can coalesce into mono‐dominant patches that outcompete C4 shortgrasses. Increased abundance of C3 species over the past seven decades, both in the presence and absence of grazing, may be related to recovery from the severe drought and dust storms of the 1930s as well as enhanced growth of C3 plants under increasing atmospheric [CO2].

A New Ending to an Old Classical Stocking Rate Study

After the Dust Bowl that gripped the Great Plains in the 1930s, researchers in several states implemented studies to determine recommended stocking rates that would sustain vegetative vigor and production. In 1946 a long-term stocking rate study was initiated to compare stocker animal production and vegetative production at light, moderate, and heavy stocking rates on western Kansas rangelands. This 20-year study showed that individual animal gains declined as stocking rate increased beyond a moderate level, and that pasture yield was inversely related to stocking rate. With increasing stocking rate, composition shifted toward low-yielding buffalograss and away from greater-yielding western wheatgrass and blue grama. However, though previously not reported, the heavy and light stocking rate treatments were continued in 1966 but were reversed in pastures from 1967 to 1971. Subsequently, after five years of the stocking reversal, the dry matter production in pastures also reversed. Following the reversal, buffalograss composition rapidly declined and western wheatgrass rapidly increased in the heavy- to light-stocked pasture. The light-stocked pasture also changed after the reversal to a heavy-stocked pasture by increasing buffalograss and decreasing western wheatgrass composition, but the change was not as drastic. The long-term repeated disturbance from stocking rate resulted in pastures being dominated by vegetation of diverging physiologic, morphologic, and canopy architectural structure. But divergent vegetative trends that developed due to long-term stocking appear to be reversible community phases that resist transition to a new ecological state. In shortgrass rangelands overutilized from heavy stocking rates, great improvements in rangeland health and productivity and shifts in plant community composition are possible within five years by simply lowering the stocking rate.

Reconsidering rest following fire: Northern mixed-grass prairie is resilient to grazing following spring wildfire

Current federal post-fire land management recommendations in the United States suggest that rangelands be rested from grazing for two growing seasons following fire to allow for proper recovery, despite the lack of empirical literature supporting this recommendation. This project was designed to determine if grazing the first growing season following a spring wildfire alters subsequent productivity and species composition of northern mixed-grass prairie. Following the April 2013 Pautre wildfire in northwestern South Dakota, 100m2 exclosures were erected in three burned pastures to simulate two growing seasons of rest. Grazing exclosures were paired with sites grazed both the first and second growing seasons following the fire and replicated across loamy and sandy ecological sites. Prior to grazing the second growing season, five 2m2 cages were placed at each grazed site to assess first-year grazing effects. Following the second growing season, productivity and species composition were determined for exclosures and cages. Productivity was greater for loamy than sandy ecological sites (loamy=2764kgha−1, sandy=2356kgha−1; P=0.0271), but was similar between grazing treatments (rested=2556kgha−1, grazed=2564kgha−1; P=0.9550). Ecological site strongly determined species composition. Loamy sites consistently contained more Pascopyrum smithii, Bouteloua gracilis and Carex duriuscula than sandy sites (30 v 0%, 18 v 8%, 4 v 1%; P=0.0004, 0.0457 and 0.0382 respectively). The effects of grazing exclusion were limited to Hesperostipa comata and the non-native Agropyron cristatum composition. H. comata was more prevalent on rested sites (22 v 15%, P=0.0096). A. cristatum experienced a grazing treatment by ecological site interaction as it was reduced by grazing on sandy sites, but was not affected on loamy sites (P=0.0226). Results do not support the notion that a two growing season rest period following fire is required in the northern mixed-grass prairie.

Native plants for roadside revegetation in Idaho

Establishing perennial plant communities on roadsides is a proactive approach to sustainable road management. The environmental and economic benefits of increasing desirable roadside vegetation include improving slope stabilization, soil conservation, and roadway safety while reducing erosion, maintenance costs, and invasive plants. This study evaluated the success of roadside revegetation on 16 sites in Idaho and on one site in adjacent southwest Montana. Study sites represent a diversity of climatic, topographic, and edaphic conditions in order to provide a variety of examples of roadside revegetation projects in 6 different ecoregions of Idaho. We measured all species’ canopy cover, including noxious weeds and other invasive plants. Of the seeded grass species, 21 of 27 established. Bluebunch wheatgrass ( Pseudoroegneria spicata (Pursh)A. Love [Poaceae]) and Idaho fescue ( Festuca idahoensis Elmer [Poaceae]) were the best-performing native grasses. Seeded grass species that consistently established but had a low mean canopy cover (2–5%) included sheep fescue ( Festuca ovina L.), western wheatgrass ( Pascopyrum smithii (Rydb.) A. Love [Poaceae]), and basin wildrye ( Leymus cinereus (Scribn. & Merr.) A. Love [Poaceae]). Seeded forbs and shrub species had low establishment success and low mean percent canopy cover. For example, no seeded forb species had more than 1% mean canopy cover and greater than 50% establishment when present in the seed mix. Seed mixes of 10 or fewer species resulted in ≥ 50% of the species establishing. Idaho noxious weeds were present in less than half of the sites (47%). Cheatgrass ( Bromus tectorum L. [Poaceae]), an invasive annual grass, occurred in 82% of the sites. These results provide species selection recommendations based on ecoregion for use in roadside revegetation projects in Idaho and portions of western Montana.

Revegetation of Medusahead-Invaded Rangelands in the Channeled Scablands of Eastern Washington

Vegetation on the Channeled Scablands of eastern Washington has been altered to a community dominated by medusahead (Taeniatherum caput-medusae [L.] Nevski). Medusahead is used by livestock but becomes unpalatable as the plant matures and seed heads develop, thus decreasing carrying capacity. The objective of this study was to determine if improved cool-season grasses could establish and persist on medusahead-infested rangelands in the region. A split-plot randomized complete block design consisting of four blocks was established at three different locations. Plots were treated with herbicides to remove all vegetation and seeded in 2010. Seeded species included introduced cool-season grass cultivars: Hycrest II crested wheatgrass (Agropyron cristatum [L.] Gaertn.), Vavilov II Siberian wheatgrass (Agropyron fragile [Roth] P. Candargy), Bozoisky II Russian wildrye (Psathyrostachys juncea [Fisch.] Nevski), and a native cool-season grass mix composed of Sherman big bluegrass (Poa secunda J. Presl), Secar Snake River wheatgrass (Elymus wawawaiensis J. Carlson & Barkworth), Bannock Thickspike wheatgrass (Elymus lanceolatus [Scribn. & J. G. Sm.] Gould), and Recovery Western wheatgrass (Pascopyrum smithii [Rydb.] Á Löve). Sherman big bluegrass was the only native species that established, and frequency was 65% at the end of the study. Hycrest II frequency was 48% at the end of the study. Vavilov II frequency was 50% at the end of the study. Sherman big bluegrass matured early in the season and had greater biomass production than Hycrest II and Vavilov II in May. The later-maturing Hycrest II and Vavilov II were similar in biomass production to Sherman big bluegrass in July. Bozoisky II had poor stand establishment and did not persist. Hycrest II, Vavilov II, and Sherman big bluegrass are forages that can be used for revegetation on the Channeled Scablands of eastern Washington.

Intermittent Growing Season Defoliation Variably Impacts Accumulated Herbage Productivity in Mixed Grass Prairie

To evaluate mechanisms by which defoliation alters grassland productivity, we examined mixed grass prairie herbage yields under recurring treatments that included hand-clipping of plots over five growing seasons at high intensity and low frequency (HILF), low intensity and high frequency (LIHF), high intensity and high frequency (HIHF), or the end of the growing season (deferred control), combined with water treatments of ambient rainfall or water addition. The study was repeated in a drier upland and mesic lowland range site. Yield was assessed as annual accumulated herbage production and, for HILF and control treatments in 2012 (year 3), evaluated separately for forbs and major graminoids. Temporal changes in the proportional yield during the growing season were also examined for the HILF and HIHF treatments. Moisture addition increased accumulated herbage, especially in the upland, and exacerbated differences among defoliation effects in select years. Productivity was greatest in the deferred controls, suggesting no treatment led to overcompensation, even with moisture addition. Among growing season treatments, yields under HILF exceeded that of the HIHF in 6 of 10 different combinations of site and year, particularly early in the study and under high moisture. Observed herbage yields suggest deferred patches of grassland may boost productivity and limit the ability of HILF defoliation to increase production, a pattern magnified by a reduction in Pascopyrum smithii in lowlands before mid-July. Accumulated herbage yield did respond favorably to HILF defoliation in uplands due to increased yields of Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths. Overall, these results suggest that any growing season defoliation reduces yields, although where defoliation is necessary at that time, production may be more likely to be maintained under HILF defoliation. More studies examining long-term growth responses to defoliation that include variation in vegetation types, environmental conditions, and defoliation regime are warranted.

Impact of grasshoppers and an invasive grass on establishment and initial growth of restoration plant species

AbstractExotic plant invasion can have dramatic impacts on native plants making restoration of native vegetation at invaded sites challenging. Though invasives may be superior competitors, it is possible their dominance could be enhanced by insect herbivores if native plants are preferred food sources. Insect herbivory can regulate plant populations, but little is known of its effects in restoration settings. There is a need to better understand relationships between insect herbivores and invasive plants with regard to their combined potential for impacting native plant establishment and restoration success. The objective of this study was to assess impacts of grasshopper herbivory and the invasive grass Bromus tectorum (cheatgrass) on mortality and growth of 17 native plant species used in restoration of critical sagebrush steppe ecosystems. Field and greenhouse experiments were conducted using moderate densities of a common, generalist pest grasshopper (Melanoplus bivittatus). Grasshoppers had stronger and more consistent impacts on native restoration plants in field and greenhouse studies than cheatgrass. After 6 weeks in the greenhouse, grasshoppers were associated with 36% mortality over all native restoration species compared to 2% when grasshoppers were absent. Herbivory was also associated with an approximately 50% decrease in native plant biomass. However, effects varied among species. Artemisia tridentata, Chrysothamnus viscidiflorus, and Coreopsis tinctoria were among the most negatively impacted, while Oenothera pallida, Pascopyrum smithii, and Leymus cinerus were unaffected. These findings suggest restoration species could be selected to more effectively establish and persist within cheatgrass infestations, particularly when grasshopper populations are forecasted to be high.

Priming seeds in aqueous smoke solutions to improve seed germination and biomass production of perennial forage species

Seeds of many forage species have dormancy, delaying germination in the field. Species from semi-arid environments may have adaptation to fire, therefore, the effects of priming seeds of common forage species in aqueous smoke solutions were studied. Seeds of eight grasses and two legumes were primed in serial dilutions of aqueous smoke solutions and then dried before germination tests. Depending on the species and concentrations of solutions, priming seeds acted independently or in interaction with light and (or) temperature to improve germination in Altai wildrye (Leymus angustus), green needlegrass (Nassella viridula), Kura clover (Trifolium ambiguum), needle-and-thread (Hesperostipa comata), northern wheatgrass (Elymus lanceolatus), orchard grass (Dactylis glomerata), plains rough fescue (Festuca hallii), Russian wildrye (Psathyrostachys juncea), and western wheatgrass (Pascopyrum smithii). Priming seeds of cicer milkvetch (Astragalus cicer) in distilled water or aqueous smoke solutions had no effect o...

Effect of Aminocyclopyrachlor on Seedling Grasses

When invasive weeds are removed with herbicides, revegetation of native species is often desirable. The extended soil activity of aminocyclopyrachlor is important for long-term weed control but could reduce recovery of native species as well. The effect of aminocyclopyrachlor applied alone or with chlorsulfuron on cool- and warm-season grass species commonly used for revegetation was evaluated. The cool-season grasses included green needlegrass, intermediate wheatgrass, and western wheatgrass, whereas the warm-season grasses were big bluestem, sideoats grama, and switchgrass. A separate experiment was conducted for each species. Aminocyclopyrachlor was applied at 91 to 329 g ha−1 alone or with chlorsulfuron from 42 to 133 g ha−1 approximately 30 d after emergence. Warm-season grasses generally were more tolerant of aminocyclopyrachlor than the cool-season grasses evaluated in this study. Switchgrass and big bluestem were the most tolerant of the warm-season species when aminocyclopyrachlor was applied at 168 g ha−1 and averaged 199 and 150% forage production, respectively, compared with the control. Green needlegrass was the most tolerant cool-season grass. Western wheatgrass was the least tolerant species evaluated because forage production only averaged 32% of the control the year after treatment and thus would not be suitable for seeding if aminocyclopyrachlor was applied. The effect of chlorsulfuron applied with aminocyclopyrachlor varied by grass species. For example, green needlegrass injury 8 wk after treatment (WAT) averaged 30 and 48% when aminocylopyrachlor was applied alone, respectively, but injury was reduced to less than 16% when aminocyclopyrachlor was applied with chlorsulfuron. However, injury on the less-tolerant intermediate wheatgrass ranged from 48 to 92% by 4 WAT when aminocyclopyrachlor was applied alone and from 60 to 86% when chlorsulfuron was included in the treatment.

Above- and below-ground responses of native and invasive prairie grasses to future climate scenarios

More intense and frequent droughts, coupled with elevated temperatures, are projected for grasslands worldwide. Although it has been suggested that alterations in temperature and precipitation will increase the success of biological invasions, studies that combine these climate change scenarios are limited. These changes in climate may increase the success of non-native, invasive plant species directly, as these species often possess traits that are favored by variable climates, or indirectly through negative impacts on native vegetation or alterations in soil microbial communities, such as arbuscular mycorrhizal (AM) fungi. The goal of our research was to assess above- and below-ground production and mycorrhizal fungal abundance of functionally similar native and invasive non-native grass species under projected climate-change scenarios. We assessed plant biomass, intra-radical AM root colonization, and relative abundance of extra-radical fungal biomass of two native (Schizachyrium scoparium (Michx.) Nash, Pascopyrum smithii (Rydb.) Á.Löve) and two invasive (Bothriochloa ischaemum (L.) Keng, Bromus inermis Leyss.) grass species subjected to increased temperature and decreased soil water availability. Regardless of temperature or soil moisture, the invasive grasses in our study displayed greater seedling growth as compared with paired native species. Invasive grasses were also generally characterized by greater intra-radical colonization by AM fungi, compared with native species. Our data suggest that invasive grasses will continue to be problematic and successfully out-compete native grasses following increased temperatures and reduced water availability, as projected by climate-change models.