Immature Seedling Growth of Two North American Native Perennial Bunchgrasses and the Invasive Grass Bromus tectorum

Pseudoroegneria spicata (Pursh) A. Löve and Elymus wawawaiensis J. Carlson & Barkworth are two native perennial grasses widely used for restoration in the Intermountain West. However, the rapid establishment and spread of Bromus tectorum L., an invasive annual grass, has led to a decline in the abundance of native perennial grasses. Proliferation of B. tectorum has been attributed to its early germination, superior cold-temperature growth, profuse root production, and high specific leaf area (SLA). To enhance restoration success, we compared B. tectorum to commercially available plant materials of two perennial rangeland bunchgrasses, P. spicata (cv. Whitmar, cv. Goldar, and Anatone Germplasm) and E. wawawaiensis (cv. Secar), for germination, seedling morphological traits, and growth rates at the immature seedling stage. We monitored germination and immature seedling growth in a growth chamber in two separate experiments, one under low (5/10°C) and the other under high (15/20°C) day/night temperatures. Compared to the average of the two perennials, B. tectorum was 93% (77%) greater at high (and low) temperature for root∶shoot length ratio, but only 14% (14%) greater for root∶shoot biomass ratio and 12% (19%) lower for SLA. This suggests that B. tectorum’s substantial investment in surface area of roots, rather than in shoot length, root biomass, or leaf area, may be responsible for the annual’s success at the early seedling stage. Compared to E. wawawaiensis, P. spicata averaged 65% (41%) higher shoot biomass, 39% (88%) higher root biomass, and 70% (10%) higher absolute growth rate, but 25% (15%) lower SLA and 15% (36%) lower specific root length (SRL) at high (and low) temperatures, respectively. Although P. spicata’s greater productivity may initially make for better seedling establishment than E. wawawaiensis, it may also prove disadvantageous in competitive or highly resource-limited environments where high SLA or SRL could be an advantage.     

Mineral Nitrogen in a Crested Wheatgrass Stand: Implications for Suppression of Cheatgrass

Cheatgrass (Bromus tectorum L.) is an exotic annual grass causing ecosystem degradation in western US rangelands. We investigated potential mechanisms by which crested wheatgrass (Agropyron cristatum L. Gaertn., Agropyron desertorum [Fisch. {Ex Link} Scult.]) suppresses the growth and invasibility of cheatgrass. Research focused on monthly mineral soil N availability and the proportional concentration of NH₄⁺-N in a crested wheatgrass community by microsite (crested wheatgrass, unvegetated interspace, shrub subcanopy) and soil depth (0–15, 15–30 cm) over a 1-yr period. Mineral soil N in crested wheatgrass microsites ranged from 0.24 to 1.66 mmol · kg^-1 and was not appreciably lower than the other microsites or other ecosystems we have measured in the Great Basin. The molar proportion of NH₄⁺-N in the mineral N pool of crested wheatgrass averaged over 85% for the year and is significantly higher than the other microsites and far greater than other plant communities we have measured in the Great Basin. We conclude that crested wheatgrass does not suppress cheatgrass by controlling mineral N below a threshold level; rather, we hypothesize that it may limit nitrification and thereby reduce NO₃^--N availability to the nitrophile cheatgrass.     

Prediction of Cheatgrass Field Germination Potential Using Wet Thermal Accumulation

Invasion and dominance of weedy species is facilitated or constrained by environmental and ecological factors that affect resource availability during critical life stages. We compared the relative effects of season, annual weather, site, and disturbance on potential cheatgrass (Bromus tectorum L.) germination in big sagebrush (Artemisia tridentata Nutt.) communities. Soil water status and temperature in the seedbed were measured continuously for 4 years on 9 big sagebrush sites in Nevada and Utah. Field plots at lower-, middle-, and upper-elevation sites were either undisturbed, or were burned, sprayed with herbicide, or both sprayed and burned. Spraying removed perennial herbaceous vegetation, whereas burning removed sagebrush. We used thermal-germination data from laboratory incubation studies of 18 cheatgrass seedlots and field soil moisture and temperature measurements to model and predict potential germination in the field plots for periods when seedbeds were continuously wet (above -0.5, -1, or -1.5 MPa) and across intermittent wet and dry periods. Season had the greatest effect on potential cheatgrass germination, followed by annual weather, and site variables (elevation and location); the effects of disturbance were minimal. Potential germination was predicted for most sites and years in spring, a majority of sites and years in fall, and few sites or years in winter. Even though disturbance has limited effects on potential germination, it can increase cheatgrass invasion and dominance by reducing perennial herbaceous species resource use and allowing increased cheatgrass growth and reproduction.     

Potential Spread of Cheatgrass and Other Invasive Species by Feral Horses in Western Colorado

The invasive grass cheatgrass (Bromus tectorum L.) presents major challenges for land management and habitat conservation in the western United States. Feral horses (Equus ferus caballus) have become overabundant in some areas of the West and can impact fragile semiarid ecosystems. Amid ongoing efforts to control cheatgrass in the Great Basin, we conducted a study to determine if feral horses contribute to the spread of cheatgrass through distribution via their feces. We collected feral horse fecal samples from Little Book Cliffs Herd Management Area in western Colorado in 2014. Fecal samples were dried, and 20 from each of 3 collection sessions were cultivated to examine germination success. Six species germinated from 18 samples (30%; mostly one plant per sample where germination occurred), including cheatgrass from 8% of samples. In a separate study we examined the diet of this same horse population using fecal plant DNA barcoding. Plant species that germinated were rare in the diet and germinated from fewer samples than expected relative to their detection in the diet. Our results suggest that feral horses could be contributing to cheatgrass propagation. Native ungulates and domestic cattle also have this potential. Although management of all large ungulates is necessary to mitigate cheatgrass spread, control of feral horse numbers is particularly necessary.     

Fire Effects on the Cheatgrass Seed Bank Pathogen Pyrenophora semeniperda

The generalist fungal pathogen Pyrenophora semeniperda occurs primarily in cheatgrass (Bromus tectorum) seed banks, where it causes high mortality. We investigated the relationship between this pathogen and its cheatgrass host in the context of fire, asking whether burning would facilitate host escape from the pathogen or increase host vulnerability. We used a series of laboratory and field experiments to address the ability of host seeds and pathogen life stages to survive fire. First, we determined the thermal death point (TDP₅₀; temperature causing 50% mortality) of seeds and pathogen propagules at two time intervals using a muffle furnace. We then measured peak fire temperatures in prescribed burns at sites in Utah and Washington and quantified seed and fungal propagule survival using pre- and postburn seed bank sampling and inoculum bioassays. Finally, we investigated the survival of both seeds and pathogen after wildfires. We found that radiant heat generated by both prescribed and wild cheatgrass monoculture fires was generally not sufficient to kill either host seeds or pathogen propagules; most mortality was apparently due to direct consumption by flames. The 5-min mean TDP₅₀ was 164°C for pathogen propagules and 148°C for host seeds, indicating that the pathogen is more likely to survive fire than the seeds. Peak fire temperature at the surface in the prescribed burns averaged 130°C. Fire directly consumed 85–98% of the viable seed bank, but prescribed burns and wildfires generally did not lead to dramatic reductions in pathogen inoculum loads. We conclude that the net effect of fire on this pathosystem is not large. Rapid postburn recovery of both host and associated pathogen populations is the predicted outcome. Postfire management of residual cheatgrass seed banks should be facilitated by the persistent presence of this seed bank pathogen.     

Cheatgrass Invasion in Salt Desert Shrublands: Benefits of Postfire Reclamation

In 1998, fires burned more than 11 330 ha of rangeland on Dugway Proving Ground in Utah's west desert. Postfire revegetation was implemented in 2 affected salt desert shrub communities (greasewood; Sarcobatus vermiculatus Hook. and black sagebrush/shadscale; Artemisia nova A. Nels; Atriplex confertifolia Torr. & Frem.) to deter cheatgrass (Bromus tectorum L.) encroachment. We monitored cheatgrass densities for 3 years after the fire in burned drill seeded, burned not-seeded, and unburned plots to assess the rate of invasion and determine the impact on cheatgrass of drill seeding perennial species. Cheatgrass invaded quickly in both shrub sites following the fires. In the greasewood site, drill seeded species germinated but did not establish. This was likely due to a combination of soil salinity and extremely dry weather conditions during the second year of the study. Drill seeded species in the black sagebrush site germinated and established well, resulting in the establishment of 16.5 perennial grasses · m^-2 and 1 356 shrubs · ha^-1. Cheatgrass densities were consistently lower in drill seeded versus not-seeded plots, although these were not always statistically different when Bonferroni comparisons were considered. The initial decrease in cheatgrass densities in drill seeded plots may have resulted from soil disturbance coupled with extremely low precipitation rather than competitive effects. Nevertheless, as seeded species mature and increase their competitive ability, we predict long-term suppression of cheatgrass in the absence of further disturbance.     

Economic Risks of Cheatgrass Invasion on a Simulated Eastern Oregon Ranch

The potential of invasive plants to alter fuel properties over time has implications for the ranchers of semiarid rangelands throughout the world. A prime example of this phenomenon is the cheatgrass (Bromus tectorum L.) invasion of the native shrub-steppe lands in Great Basin of the western United States. The purpose of this study is to develop a bioeconomic model that optimizes simulated ranch behavior given the beginning stages of cheatgrass invasion on a public forage allotment. The bioeconomic model is applied to a typical eastern Oregon 300 cow-calf ranch. Livestock production decisions are simulated over a 40-yr planning horizon using a multiperiod linear programming model. Results showed changes in profit-maximizing ranch management strategies in the form of decreased optimal stocking rates and forage substitution. The net present value of the simulated ranch’s income stream declined, and the probability that the ranch cannot meet its full costs of livestock production and would exit the industry increased as a result. These economic impacts were more pronounced with decreased sale price. Sensitivity analysis showed that overall results in terms of ranch behavior were specific neither to the assumed discount rate nor to the assumed percentage of cheatgrass cover (as long as this percentage is within the reference state) on the public grazing allotment. This study introduces a method for managers to quantify impacts on ranches from fuel-altering invasive plants on public lands, emphasizing the importance of including information about native and invasive forage production characteristics and wildfire frequency as a function of the state of invasion.     

Defoliation Intensity and Simulated Grazing Strategy Effects on Three C4 Rangeland Bunchgrasses

Defoliation intensity and timing are two important factors determining plants response to grazing. These factors can be managed by adjusting stocking rate and applying a grazing strategy. In a 6-yr clipping experiment conducted in northwestern Argentina, we assessed the effect of different defoliation intensities (~ 30%, ~ 50%, and ~ 70% removal of the annually produced aboveground biomass) and simulated grazing strategies (continuous grazing, two-paddock rest-rotation, three-paddock rest-rotation, dormant season grazing) on plots of three C4 native bunchgrasses (Pappophorum vaginatum, Trichloris crinita, and Digitaria californica). Response variables were mean and trend of clipped-off biomass during the 6 yr of treatments, number of inflorescences, and aboveground biomass produced on the year following treatments end (to evaluate residual effect of treatments). Results were species dependent. Mean clipped-off biomass increased with defoliation intensity in T. crinita and D. californica. However, defoliation intensity negatively affected clipped-off biomass trend in T. crinita and the production of P. vaginatum and T. crinita during “residual effect” evaluation. The three species responded positively at least in one response variable to the amount of rest periods in the grazing strategy. Our results are not fully consistent with the concept that forage production is more influenced by defoliation intensity than by grazing strategy: In two of the three species, grazing strategy presented greater impact on response variables than defoliation intensity. When significant “defoliation intensity × grazing strategy” was detected, intensity tended to be more detrimental as grazing strategy allows fewer rest periods. We observed a residual effect of treatments in the three species (generally, negative effect of defoliation intensity and positive effect of grazing strategies with more rest periods). Our results show that dormant season utilization and rest periods are beneficial for maximizing mean clipped-off biomass and ensuring clipped-off biomass trend. High defoliation intensities can maximize short-term clipped-off biomass, but it may produce negative residual effects and trends.     

Effects of Nitrogen Availability and Cheatgrass Competition on the Establishment of Vavilov Siberian Wheatgrass

Cheatgrass (Bromus tectorum L.) is the most widespread invasive weed in sagebrush ecosystems of North America. Restoration of perennial vegetation is difficult and land managers have often used introduced bunchgrasses to restore degraded sagebrush communities. Our objective was to evaluate the potential of ‘Vavilov’ Siberian wheatgrass (Agropyron fragile [Roth] P. Candargy) to establish on cheatgrass-dominated sites. We examined Vavilov establishment in response to different levels of soil nitrogen availability by adding sucrose to the soil to promote nitrogen (N) immobilization and examined cheatgrass competition by seeding different levels of cheatgrass. We used a blocked split-split plot design with two sucrose levels (0 and 360 g · m⁻²), two levels of Vavilov (0 and 300 seeds · m⁻²), and five levels of cheatgrass (0, 150, 300, 600, and 1 200 seeds · m⁻²). Seeding was conducted in fall 2003 and 2004, and measurements were taken in June 2004, 2005, and 2006. Sucrose addition decreased availability of soil nitrate but not orthophosphate. In the first year after seeding, sucrose reduced cheatgrass density by 35% and decreased both cheatgrass biomass per square meter and seed production per square meter by 67%. These effects were temporary, and by the second year after seeding, there was a sevenfold increase in cheatgrass density. As a result, the effects of sucrose addition were no longer significant. Sucrose affected Vavilov growth, but not density, during the first year after seeding. Vavilov density decreased as cheatgrass seeding density increased. Short-term reductions in N or cheatgrass seed supply did not have long-term effects on cheatgrass and did not increase Vavilov establishment. Longer-term reductions in soil N, higher seeding densities, or more competitive plant materials are necessary to revegetate areas dominated by cheatgrass.     

Comparison of Postfire Soil Water Repellency Amelioration Strategies on Bluebunch Wheatgrass and Cheatgrass Survival

Soil water repellency can limit postfire reseeding efforts and thus increase the susceptibility of a site to weed invasion. We evaluated the effectiveness of wetting agents and simulated anchor chaining for improving seedling growth and survival in water-repellent soil, for the native perennial bluebunch wheatgrass (Pseudoroegneria spicata) and invasive annual cheatgrass (Bromus tectorum). Research was performed in a glasshouse, on 20-cm-diameter soil cores that were excavated from underneath burned Utah juniper (Juniperus osteosperma) trees. The experiment was arranged as a randomized split-plot design, with the two grass species sown separately under four soil treatments: 1) no treatment (control), 2) simulated anchor chaining (hereafter referred to as “till”), 3) wetting agent, and 4) till plus wetting agent. Soil water content was highest in the wetting agent treatment, lower for till, and lowest in the control. Overall, the response of bluebunch wheatgrass and cheatgrass was similar among treatments. At the conclusion of the study, wetting agent cores had twice as many seedlings as the control, while the till and control were similar. Despite a lower number of seedlings, tilling in general resulted in the same level of biomass as the wetting agent treatment. Overall, biomass in the till and wetting agent treatments was at least twofold higher than the control. No benefit was found in applying both till and wetting agent treatments together in comparison to just applying wetting agent. Because of a lack of correlation between glasshouse and field settings the results of this study need to be interpreted with caution. Our data may indicate that if cheatgrass is not already present on the site, anchor chaining or treating the soil with wetting agent can increase establishment of seeded species.     

Impact of Native Grasses and Cheatgrass (Bromus tectorum) on Great Basin Forb Seedling Growth

Re-establishing native communities that resist exotic weed invasion and provide diverse habitat for wildlife are high priorities for restoration in sagebrush ecosystems. Native forbs are an important component of healthy rangelands in this system, but they are rarely included in seedings. Understanding competitive interactions between forb and grass seedlings is required to devise seeding strategies that can enhance establishment of diverse native species assemblages in degraded sagebrush communities. We conducted a greenhouse experiment to examine seedling biomass and relative growth rate of common native forb species when grown alone or in the presence of a native bunchgrass or an exotic annual grass. Forb species included bigseed biscuitroot (Lomatium macrocarpum [Nutt. ex Torr. & A. Gray] J.M. Coult. & Rose), sulphur-flower buckwheat (Eriogonum umbellatum Torr.), hoary aster (Machaeranthera canescens [Pursh] Gray), royal penstemon (Penstemon speciosus Douglas ex Lindl.), and Munro's globemallow (Sphaeralcea munroana [Douglas ex Lindl.] Spach ex Gray); and neighboring grass species included bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey), Sandberg bluegrass (Poa secunda J. Presl); and cheatgrass (Bromus tectorum L.). Forbs and grasses were harvested after 6, 9, or 12 wk of growth for biomass determination and calculation of relative growth rates (RGR) of forbs. Neither bunchgrass reduced biomass of any forb. RGR was reduced for royal penstemon when grown with either native grass and for Munro's globemallow when grown with bottlebrush squirreltail. Although only assessed qualitatively, forbs with vertically oriented root morphologies exhibited no reduction in RGR when grown with native grasses, compared to forbs with dense lateral branching, similar to the root morphology of native grasses. Biomass of forbs was reduced by 50% to 91% and RGR by 37% to 80% when grown with cheatgrass. Understanding native forb interactions with native grasses and cheatgrass will aid land managers in selecting effective seed mixes and making better use of costly seed.     

四种多年生禾本科牧草引种试验

为选择适于本地区栽培的高产、优质多年生禾本科牧草,于2014年至2015年在同仁县年都乎乡进行不同多年生禾草的引种试验。结果表明,四种多年生禾草都能适应本地区,但相比之下,在平均草层高度和产量方面多叶老芒麦明显高出其它三种牧草,更适宜在该地区大量种植,可以作为人工草地建设和天然草场改良的优良牧草。     

Incorporating Seeds in Activated Carbon Pellets Limits Herbicide Effects to Seeded Bunchgrasses When Controlling Exotic Annuals

Revegetation of exotic annual grass ? invaded rangeland with preemergent herbicides is challenging because seeding is delayed until herbicide toxicity has diminished, but at this time, exotic annuals can be reinvading. Incorporating seeds into activated carbon pellets may allow seeding to occur at the same time as exotic annuals are controlled with a preemergent herbicide because activated carbon can neutralize the herbicide in the microsite around seeds. I evaluated using activated carbon pellets with six species seeded at the same time imazapic was applied to control exotic annual grasses at two sites. Two of the six species establish enough at one site to evaluate the effects of pellets. These two bunchgrasses had greater density and growth (height, leaf length, number of stems and leaves) when incorporated into activated carbon pellets compared with seeded as bare seed. This demonstrates activated carbon pellets can be used to protect seeded bunchgrasses from imazapic applied to control exotic annuals.     

多年生禾本科牧草生产性能的研究

本文对河南草地８种主要优良牧草的生物学特性及经济性状进行了研究。结果表明,这些牧草适应性强,生长快,绿期长,生产性能稳定,产量高而且饲料品质好。这些研究结果为优良禾草的科学应用提供理论依据。     

多年生黑麦草愈伤组织诱导和植株再生

对多年生黑麦草Lolium perenne品种"德比"成熟种子的愈伤组织诱导和植株再生进行了探索研究.结果表明:在附加10 mg/L 2,4-D,500 mg/L CH(水解酪蛋白),0.5 mg/L 6-BA和0.5 mg/L NAA的N6培养基中愈伤诱导率最高,达85%.分化培养基以附加1 mg/L、6-BA、0.5 mg/L KT的N6培养基为最优,分化率为77. 73%.在大量元素减半的N6培养基中附加30 g/L蔗糖及0.2 mg/L NAA进行生根培养,生根率达100%.     

Shrub Microsite Influences Post-Fire Perennial Grass Establishment

Woody plants can cause localized increases in resources (i.e., resource islands) that can persist after fire and create a heterogeneous environment for restoration. Others have found that subcanopies have increased soil organic matter, nitrogen, and carbon and elevated post-fire soil temperature. We tested the hypothesis that burned sagebrush subcanopies would have increased seedling establishment and performance of post-fire seeded perennial bunchgrasses compared to burned interspaces. We used a randomized complete block design with five study sites located in southeast Oregon. The area was burned in a wildfire (2007) and reseeded in the same year with a seed mix that included non-native and native perennial bunchgrasses. Seedling density, height, and reproductive status were measured in October 2008 in burned subcanopy and interspace microsites. Non-native perennial grasses had greater densities than native species (P < 0.001) and were six times more abundant in burned subcanopies compared to burned interspaces (P < 0.001). Density of natives in burned subcanopies was 24-fold higher than burned interspaces (P = 0.043). Seedlings were taller in burned subcanopies compared to burned interspaces (P = 0.001). Subcanopy microsites had more reproductive seedlings than interspace microsites (P < 0.001). Our results suggest that under the fire conditions examined in this study, pre-burn shrub cover may be important to post-fire restoration of perennial grasses. Determining the mechanisms responsible for increased seeding success in subcanopy microsites may suggest tactics that could be used to improve existing restoration technologies.