Thomas A. Monaco

Contrasting responses of Intermountain West grasses to soil nitrogen

The mechanisms responsible for soil-N-mediated species replacement of native perennial grasses by the invasive annual grasses cheatgrass (Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae [L.] Nevski) on rangelands are not completely understood. In addition, the contributions of distinct forms of inorganic N (i.e., NH 4 + and NO 3 -) to these shifts in species composition are currently unclear. Consequently, we conducted a greenhouse experiment to test 2 hypotheses: 1) that low N availability reduces growth (root and shoot) and N allocation of invasive annual seedlings more than native perennial species, and 2) that seedling growth and N allocation of invasive annual grasses is more responsive than native perennial grasses when supplied with NO 3 - relative to NH 4 +. We grew seedlings of 2 annual grasses and the native perennial grasses bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love), and 4 populations of squirreltail (Elymus elymoides [Raf.] Swezey; E. multisetus [J.G. Smith] M.E. Jones) in separate pots and exposed them to treatments differing in N form and availability for 17 weeks. Unexpectedly, root and shoot growth of annual grasses were equal or greater than native perennial grasses under low N availability. Annual grasses took up more NO 3 - and allocated more growth and N to shoots than the perennial grasses (P < 0.05). Perennial grasses had significantly greater root:shoot dry mass ratios than the invasive annual grasses across treatments (P < 0.05). Invasive annual and native perennial grasses both had greater (P < 0.05) shoot and root mass and allocated more N to these structures when supplied with NO 3 - relative to NH 4 +. The ecological implications of these growth and N allocation patterns in response to N availability and form provide important clues regarding the specific traits responsible for differences in competitive ability between invasive annual and native perennial grasses on semiarid rangelands.

Medusahead Control with Fall- and Spring-Applied Herbicides on Northern Utah Foothills1

Medusahead is an aggressive, nonnative, winter annual grass that infests rangelands in the western United States. Its ability to rapidly spread, outcompete native vegetation, and destroy forage potential is a primary concern for landowners and land managers exposed to this weed. Prescribed burns were conducted at a low- and high-litter site in northern Utah prior to conducting experiments to evaluate the effects of fall and spring applications of sulfometuron at 39 or 79 g ai/ha and imazapic at 70 or 140 g ai/ha on medusahead and associated perennial grasses, annual and perennial forbs, and bare ground cover. Large differences in pretreatment medusahead litter between the sites resulted in less surface area burning at the low-litter site (∼10%) compared to the high-litter site (∼80%). Higher herbicide rates significantly increased medusahead control and bare ground cover; however, this rate affect largely depended on site, season, and herbicide. The low- and high-litter sites did not differ significantly in perennial grass cover 2 yr after burning. Annual forb cover was greater, but perennial forb cover was lower at the low-litter site compared to the high-litter site. Several treatment combinations were identified as having the potential to maintain greater than 50% medusahead control in the second year after herbicide applications. These results collectively demonstrate that potential exists to successfully control medusahead and produce a window of opportunity to reintroduce a greater abundance of perennial species back into the plant community via seeding. Nomenclature: Imazapic; sulfometuron; medusahead, Taeniatherum caput-medusae (L.) Nevski, #3 ELYCM. Additional index words: Prescribed fire, Bromus tectorum L., Aegilops cylindrical Host., invasive annual grass, Great Basin, revegetation, BROTE, AEGCY.

Mediterranean annual grasses in western North America: kids in a candy store

In this issue of Plant and Soil, Blank and Sforza (2007) contribute to understanding of how exotic annual grasses invade ecosystems in the western United States. Their findings, that medusahead wildrye (Taeniatherum caput-medusae [L.] Nevski) was most productive on non-invaded US soil and that plants from US-derived seeds may have evolved to utilize higher nutrient concentrations, parallel other results that suggest soils of vulnerable western US ecosystems are functionally different (i.e., more available-nutrient rich) than soils where these weeds are native and noninvasive (Blumenthal 2005; Davis et al. 2000). While it has been well established that exotic annual grasses can perpetuate their own environment by fostering increased available nutrients (e.g., Ehrenfeld and Scott 2001; Norton et al. 2003), we must remember, for the sake of ecological restoration, that initial invasiveness is caused by chronic disturbances that disrupt native nutrient and organic matter cycles and increase nutrient availability. The principal difference between western US ecosystems and those where invasive annual grasses are native is the amount of time during which chronic disturbances have occurred. In the Mediterranean region, intensive management of grass and shrubland ecosystems depleted nutrients long ago, so that native vegetation is adapted to a “here today, gone tomorrow” strategy. In ecosystems of the arid and semiarid western USA, perennial-plantdominated native nutrient cycles were disrupted by intensive land use much more recently. Chronic disturbances in the form of extensive grazing and altered fire regimes began to unlock nutrients stored in soil organic matter (SOM) for millennia. When seeds of exotic annual grasses arrived they found that the candy store was open. In this commentary, we review evidence for major shifts in ecosystem processes across the semiarid western USA and we call for more research that links results of ecological restoration efforts to the growing body of knowledge about interactions between invasive annuals and invaded environments. In western US ecosystems vulnerable to weed invasion, the consequence of almost any type of ecosystem disruption is a shift from immobilizing, Plant Soil (2007) 298:1–5 DOI 10.1007/s11104-007-9364-8

Variable Impacts of Imazapic Rate on Downy Brome (Bromus tectorum) and Seeded Species in Two Rangeland Communities

Abstract The herbicide imazapic is registered for use on rangelands and provides effective short-term control of certain invasive annual grasses. However, details about optimal application rates for downy brome and susceptibility of simultaneously seeded species are lacking. Thus, we investigated downy brome and seeded species responses to variable rates of imazapic (0, 35, 70, 105, and 140 g ai/ha) in two plant communities (salt desert shrub and Wyoming big sagebrush). In autumn 2003, plots were treated with imazapic and seeded with one of five perennial plant materials (Siberian wheatgrass [‘Vavilov’ and the experimental source Kazak]; prostrate kochia [‘Immigrant’ and the experimental source 6X], and Russian wildrye [‘Bozoisky II’]). Downy brome cover and seeded species establishment were evaluated in spring 2004 and 2006. Downy brome cover in 2004 decreased with increasing imazapic rate at both sites, although more so at the Wyoming big sagebrush site. In 2006, no difference in downy brome cover existed among herbicide rates at the Wyoming big sagebrush site. At the salt desert shrub site, the high rate of imazapic reduced downy brome cover by about 25% compared to untreated plots. ‘Vavilov’ Siberian wheatgrass was the only seeded species with lower downy brome cover in 2006 than 2004. Seeded species establishment increased with imazapic rate in the salt desert shrub community, but in the Wyoming big sagebrush community it peaked at intermediate rates and declined at higher rates. Variation in downy brome control and seeded species establishment might have been associated with differences in precipitation, soil organic matter, and disturbance history between sites. Overall, imazapic was useful for helping establish desirable perennial species, but unless downy brome is reduced below a critical threshold, favorable precipitation can return sites to pretreatment levels within two years. Nomenclature: Imazapic; downy brome, Bromus tectorum L. BROTE; Siberian wheatgrass, Agropyron fragile (Roth) P. Candargy; Russian wildrye, Psathyrostachys juncea (Fisch.) Nevski; prostrate kochia, Bassia prostrata (L.) A. J. Scott; Wyoming big sagebrush, Artemisia tridentata Nutt. var. wyomingensis (Beetle & Young) S. L. Welsh. Nomenclature of all plants follow the USDA–NRCS PLANTS database (http://plants.usda.gov/).

Forage nutritional characteristics of orchardgrass and perennial ryegrass at five irrigation levels

the major contributors to NDF (Fisher et al., 1995). Laboratory measures of NDF are correlated with volunAs water resources become limiting, the need to produce stable tary intake (Casler and Vogel, 1999). Fisher et al. (1995) amounts of highly nutritional forage increases. An understanding of how levels of irrigation affect crude protein (CP), digestible neutral reported that energy is closely related to the digestibility detergent fiber (dNDF), in vitro true digestibility (IVTD), and neutral of NDF (dNDF) in forage grasses. Grant (2002) redetergent fiber (NDF) is critical in pasture forage management. Cultiported that NDF digestion can range from 2 to 20% vars of orchardgrass (Dactylis glomerata L.) and perennial ryegrass h 1 in dairy cows (Bos taurus). Oba and Allen (1999) (Lolium perenne L.) were established under a line-source irrigation reported that an increase in forage dNDF resulted in system to evaluate the effect of five water levels (WLs) and three increased dry matter intake and milk yield. They further harvest dates on concentrations of CP, dNDF, IVTD, and NDF. concluded that for every 1% unit increase in dNDF, Perennial ryegrass forage had higher CP, dNDF, and IVTD and lower NDF concentrations than orchardgrass at all harvest dates and within there was a 0.18-kg increase in dry matter intake and a WLs. The most notable trend in nutritional value across WLs was 0.03-kg increase in body weight in dairy cows. Selection the near linear increase in CP ranging from 175 g kg 1 at the wettest for increased CP and in vitro dry matter digestibility WL to 217 g kg 1 at the driest WL. Digestible NDF ranged from 709 in cool-season grasses has resulted in subsequent yield to 757 g kg 1 at corresponding WLs. These trends were particularly reductions in smooth bromegrass (Bromus inermis evident later in the growing season. Orchardgrass maturity (early vs. Leyss.) and reed canarygrass (Phalaris arundinacea L.) late) had little effect on forage nutritional characteristics across WLs. (Casler, 1998; Casler and Vogel, 1999). Combined over WLs, tetraploid perennial ryegrass cultivars averaged higher concentrations of CP, IVTD, and dNDF and lower NDF values Hall (1998) found that maximum forage nutrition was compared with diploid cultivars. In general, as water stress increased, achieved when orchardgrass, smooth bromegrass, and forage nutritional value (i.e., CP and dNDF) increased. reed canarygrass were harvested at 35to 45-d intervals. In another study (Turner et al., 1996), increased CP and lower NDF concentrations were observed under early I in maximizing productivity of irrigated pasand frequent defoliation compared with a hay managetures has escalated with the increased restrictions ment system for festulolium [Xfestulolium braunii (K. on grazing public lands in the western USA. Under Richt) A. Camus], orchardgrass, and prairie grass (Broadequate irrigation, cool-season grass pastures repremus catharticus M. Vahl). Similarly, CP in stockpiled sent some of the most productive grazing lands throughforage of 11 cool-season grasses declined by 55% from out the West (Bateman and Keller, 1956). Increasing June to September (Suleiman et al., 1999). Under the human population and droughty growing conditions same line source, orchardgrass cultivars had higher dry place additional demands on available irrigation water. matter yield and increased water use efficiency than As a result, producers are required to use less water perennial ryegrass cultivars (Jensen et al., 2001, 2002). while trying to maintain stable amounts of highly nutriA line-source irrigation system was developed to evaltious forage. Historically, germplasm improvement in uate plant growth under a gradient of WLs (Hanks et orchardgrass and forage-type perennial ryegrass has foal., 1976). This system has been used to study the recused on forage traits, disease resistance, and agronomic sponses of cool-season grasses to controlled irrigation adaptation to temperate areas (Balasko et al., 1995; levels (Johnson et al., 1982; Asay and Johnson, 1990; Christie and McElroy, 1995; Jung et al., 1996; Casler et Asay et al., 2001; Jensen et al., 2001; Waldron et al., al., 2000). 2002). Literature is limited regarding the effects of irriForage nutrition can be measured by the relative pergation on forage nutritional characteristics under reformance of animals when forage is fed to livestock. peated harvesting. Animal performance is highly influenced by nutrient Objectives of this study were to study the trends in concentration, intake, and digestibility (Buxton et al., CP, dNDF, IVTD, and NDF for nine cultivars of or1996). In the absence of feeding trials, forage nutritive value is often evaluated by measuring such characterischardgrass and seven of perennial ryegrass across an tics as CP, NDF, acid detergent fiber, IVTD, and hemiirrigation gradient. A secondary objective was to evalucellulose (Pavetti et al., 1994). Cell wall constituents are ate the effect of ploidy level in perennial ryegrass and maturity in orchardgrass on any observed differences USDA-ARS, Forage and Range Res. Lab., Utah State Univ., Logan, and trends in forage nutritive value across the irrigaUT 84322-6300. Joint contribution of the USDA-ARS and the Utah tion gradient. Agric. Exp. Stn. Journal Paper no. 7468. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the USDA or Utah State Univ. Received Abbreviations: CP, crude protein; dNDF, digestible neutral detergent 13 May 2002. *Corresponding author (kevin@cc.usu.edu). fiber; IVTD, in vitro true digestibility; NDF, neutral detergent fiber; NIRS, near infrared reflectance spectroscopy; WL, water level. Published in Agron. J. 95:668–675 (2003).

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

Abstract 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. tectorums substantial investment in surface area of roots, rather than in shoot length, root biomass, or leaf area, may be responsible for the annuals 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. spicatas 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.

Linking Plant Spatial Patterns and Ecological Processes in Grazed Great Basin Plant Communities

Abstract Observational studies of plant spatial patterns are common, but are often criticized for lacking a temporal component and for their inability to disentangle the effect of multiple community-structuring processes on plant spatial patterns. We addressed these criticisms in an observational study of Great Basin shrub-steppe communities that have been converted to a managed grazing system of planted crested wheatgrass (Agropyron cristatum [L.] Gaertn.) stands. We hypothesized that intraspecific interference and livestock grazing were important community-structuring processes that would leave unique spatiotemporal signatures. We used a survey-grade global positioning system to quantify crested wheatgrass spatial patterns along a chronosequence of stands that differed only in time since planting (9–57 yr), as well as in a 57-yr-old grazing exclosure to examine pattern formation in the absence of grazing. Three replicate survey plots were established in each stand, and a total of 6u200a197 grasses were marked with a spatial error of ≤u200a2 cm. The data were analyzed using L-statistics in program R, and hypothesis testing was conducted using Monte Carlo simulation procedures. We detected fine-scale regularity, frequently considered a sign of interference via resource competition, in all stands including the exclosure. Coarser-scale aggregation, which we attributed to the effects of prolonged grazing disturbance, was only detected in the oldest grazed stand. Our results suggest that interference acts over finer spatial and temporal scales than grazing in structuring these stands, reinforcing the importance of interference in semiarid communities. Analysis of exclosure data suggests that, in the absence of grazing, crested wheatgrass stands organize into a statistically regular pattern when primarily influenced by interference. In the presence of prolonged grazing, crested wheatgrass stands become more heterogeneous over time, likely a result of seedling mortality via disturbance by cattle.

Stress-induced metabolic differences between populations and subspecies of Artemisia tridentata (sagebrush) from a single hillside

Abstract Big sagebrush or Artemisia tridentata Nutt. ssp. vaseyana grows at slightly higher, cooler, and drier sites than does A. tridentata ssp. tridentata . The two sagebrush subspecies and natural hybrids between them are found along an elevational gradient in Salt Creek Canyon, near Nephi, UT, USA, where the parent populations are separated by 85xa0m in elevation and 1.1xa0km along the transect. In 1993, three gardens were established with seedlings from five populations from different elevations planted in each garden. Physiological measurements of carbon isotope ratios, chlorophyll fluorescence, and respiratory heat and CO 2 production show adaptation to the site of origin. When transplanted to foreign sites, stress was noted. Sagebrush has persistent leaves that are metabolically active all year. Seasonal changes in temperature promote metabolic responses in sagebrush that differ with population and garden.

Sulfosulfuron effects on growth and photosynthesis of 15 range grasses

We conducted greenhouse experiments to compare photosynthetic and growth responses of 2 invasive annual grasses (downy brome = Bromus tectorum L. and medusahead = Taeniatherum caput-medusae (L.) [Nevski]), 6 caespitose grasses, and 7 rhizomatous grasses to the herbicide sulfosulfuron (1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea). Our objectives were to identify general patterns of species responsiveness and test the hypothesis that sulfosulfuron induced reduction in photosynthetic activity and shoot growth would be more pronounced in small relative to larger plants. Small plants in a spring experiment and large plants in a summer experiment were treated with sulfosulfuron (70 g ai ha -1 ). Wildryes and bromes were consistently injured; whereas, 5 of the 7 wheatgrasses were not susceptible to sulfosulfuron. Rhizomatous grasses generally experienced greater damage from sulfosulfuron than caespitose grasses. These results suggest that sulfosulfuron would provide a useful rangeland management tool to control unwanted invasive annual grasses without significantly hindering growth and physiology of desirable rangeland grasses.

Evaluation of elemental allelopathy in Acroptilon repens (L.) DC. (Russian Knapweed)

Although Acroptilon repens (L.) DC. (Russian knapweed) is known to concentrate zinc (Zn) in upper soil layers, the question of whether the elevated Zn has an allelopathic effect on restoration species has not been addressed. Experiments were conducted to investigate whether soils collected from within infestations of A. repens (high-Zn) inhibit the germination or growth and development of desirable restoration species, compared to soils collected adjacent to an A. repens infestation (low-Zn). Four bioassay species [Sporobolus airoides (Torrey) Torrey (alkali sacaton), Pseudoroegneria spicata (Pursh) A. Love (bluebunch wheatgrass), Psathyrostachys juncea (Fischer) Nevski (Russian wildrye) and A. repens] were germinated in a growth chamber and grown in a greenhouse in both soils and received treatments for the alleviation of Zn toxicity (P, Fe, Fe-oxide, and soil mixing) to isolate the effects of elevated soil Zn on plant performance. Percent germination, total plant biomass, tiller and stem number, inflorescence number, and tissue metal levels were compared among soil types and treatments for each species. There was no evidence from any of the indicators measured that high-Zn soils reduced plant performance, compared to low-Zn soils. Tissue Zn levels barely approached the lower range of phytotoxic levels established for native grasses. Older plants with longer exposure times may accumulate higher Zn concentrations. S. airoides and A. repens both had higher biomass in the high-Zn soil, most likely due to increased macronutrient (N and P) availability. As the Zn levels in the soils used in this study were much higher than any levels previously reported in soils associated with A. repens, it is unlikely that the elevation of soil Zn by A. repens will hinder germination or growth and development of desirable grasses during establishment.