Evaluating the Effectiveness of Low Soil-Disturbance Treatments for Improving Native Plant Establishment in Stable Crested Wheatgrass Stands

Past seedings of crested wheatgrass (Agropyron cristatum [L.] Gaertn. and A. desertorum [Fisch. ex Link] Schult.) have the potential to persist as stable, near-monospecific stands, thereby necessitating active intervention to initiate greater species diversity and structural complexity of vegetation. However, the success of suppression treatments and native species seedings is limited by rapid recovery of crested wheatgrass and the influx of exotic annual weeds associated with herbicidal control and mechanical soil disturbances. We designed a long-term study to evaluate the efficacy of low-disturbance herbicide and seed-reduction treatments applied together or alone and either once or twice before seeding native species. Consecutive herbicide applications reduced crested wheatgrass density for up to 6 ? 7 yr depending on study site, but seed removal did not reduce crested wheatgrass abundance; however, in some cases combining herbicide application with seed removal significantly increased densities of seeded species relative to herbicide alone, especially for the site with a more northern aspect. Although our low-disturbance treatments avoided the pitfalls of secondary exotic weed influx, we conclude that crested wheatgrass suppression must reduce established density to values much lower than 4 ? 7 plants/m², a range that has not been obtained by ours or any previous study, in order to diminish its competitive influence on seed native species. In addition, our results indicated that site differences in environmental stress and land-use legacies exacerbate the well-recognized limitations of native species establishment and persistence in the Great Basin region.     

Seedling Interference and Niche Differentiation Between Crested Wheatgrass and Contrasting Native Great Basin Species

Interference from crested wheatgrass (Agropyron cristatum [L.] Gaertn.) seedlings is considered a major obstacle to native species establishment in rangeland ecosystems; however, estimates of interference at variable seedling densities have not been defined fully. We conducted greenhouse experiments using an addition-series design to characterize interference between crested wheatgrass and four key native species. Crested wheatgrass strongly interfered with the aboveground growth of Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young), rubber rabbitbrush (Ericameria nauseosa [Pall. ex Pursh] G. L. Nesom & Baird subsp. consimilis [Greene] G. L. Nesom & Baird), and to a lesser extent with bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve). Alternatively, bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey subsp. californicus [J. G. Sm.] Barkworth) and crested wheatgrass had similar effects on each other’s growth, and interference ratios were near 1.0. Results indicate that the native grasses more readily establish in synchrony with crested wheatgrass than these native shrubs, but that once established, the native shrubs are more likely to coexist and persist with crested wheatgrass because of high niche differentiation (e.g., not limited by the same resource). Results also suggest that developing strategies to minimize interference from crested wheatgrass seedlings emerging from seed banks will enhance the establishment of native species seeded into crested wheatgrass–dominated communities.     

冰草的远缘杂交及杂种分析

蒙古冰草隶属于冰草属的二倍体种，原产于内蒙古。航道冰草是从北美引进的栽培品种隶属于扁穗冰草种，亦为二倍体种，为了将蒙古冰草的优良抗性基因和航道冰草的优良品质基因相结合，进行二倍体种间的远缘杂交。杂种Ｆ１全部为二倍体，其形态学特征介于双亲之间。杂种Ｆ１ ＰＭＣ ＭⅠ的染色体平均配对构型为：２．０９Ⅰ，４．８６Ⅱ，０．４８Ⅲ，０．２４Ⅳ及０．２９Ⅴ。     

Crested Wheatgrass Defoliation Intensity and Season on Medusahead Invasion

The objective of this study was to determine the effects of crested wheatgrass (Agropyron cristatum [L.] Gaertn.) defoliation intensity and timing on medusahead density and biomass. We hypothesized that crested wheatgrass defoliation greater than 60% during the spring would provide maximum medusahead (Taeniatherum caput-medsae [L.] Nevski subsp. asperum [Simk.] Melderis; taxonomy from US Department of Agriculture) density and biomass. Eighteen treatments (six defoliation levels, three seasons of defoliation) were applied to 2-m² plots in a randomized complete block design on two sites with varying clay content. Blocks were replicated five times at each site. Plants were clipped in 2004 and 2005. Crested wheatgrass was hand clipped to defoliation levels of 0%, 20%, 40%, 60%, 80%, and 100% in the spring, summer, or fall. Density of crested wheatgrass and medusahead was sampled in June 2005 and 2006, but their biomass was harvested only in 2006. Data were analyzed with least square means analysis of variance. Over the two seasons, site had much more of an impact on medusahead invasion than either defoliation intensity or timing of defoliation. The results support previous suggestions that clayey soils favor medusahead and that perennial grasses with high biomass can resist this invasive species. On the clayey site where medusahead did persist, fall defoliation of crested wheatgrass reduced the density of this invasive species by 50% or more compared to spring defoliation. Given the developmental pattern of medusahead, the goal of any management program should be to maximize resource use by the desirable species during April to late July.     

Plant Establishment in Masticated Utah Juniper Woodlands

Juniper (Juniperus spp.) encroachment into sagebrush (Artemisia spp.)-bunchgrass communities has reduced understory cover on millions of hectares of semiarid rangelands. Mechanical masticators shred trees to restore desirable vegetation and reduce the potential for catastrophic wildfire. Mechanical mastication where juniper density is high and perennial grass cover is low brings a risk of invasive weed dominance unless perennial species are established. To determine whether juniper mastication favors annual- or perennial-grass establishment, we compared seedling emergence, tillers, and aboveground biomass of cheatgrass (Bromus tectorum L.) and Anatone bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve). Comparisons were made among hand-planted rows between and under juniper canopies of masticated and adjacent untreated control areas at three locations in Utah. Bluebunch wheatgrass had 16% (95% CI: 11–21) and cheatgrass had 10% (95% CI: 5–15) fewer seedlings emerge per row in masticated than untreated areas (P < 0.001). However, bluebunch wheatgrass had 3.2 (95% CI: 2.0–5.2) times more tillers and 1.9 (95% CI: 1.6–2.2) times more aboveground biomass per row in masticated than untreated areas (P < 0.001). Similarly, cheatgrass had 2.3 (95% CI: 1.5–3.8) times more tillers, 2.0 (95% CI: 1.7–2.4) times more aboveground biomass, and 11.4 (95% CI: 6.3–20.7) times more spikelets per row in masticated than untreated areas (P < 0.001). This increased seedling growth in masticated areas was associated with increased inorganic nitrogen and soil water compared to untreated areas. Because mastication improves the growth of both cheatgrass and bluebunch wheatgrass seedlings, it could support dominance by either annual- or perennial-life forms. To avoid cheatgrass dominance where perennial understory cover is limited and cheatgrass propagule pressure is high, mastication should be accompanied by seeding desirable perennial species such as Anatone bluebunch wheatgrass.     

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 &lsqb;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.     

Native Plant Growth and Seedling Establishment in Soils Influenced by Bromus Tectorum

The invasion of 40 million hectares of the American West by cheatgrass (Bromus tectorum L.) has caused widespread modifications in the vegetation of semi-arid ecosystems and increased the frequency of fires. In addition to well-understood mechanisms by which cheatgrass gains competitive advantage, it has been implicated in reducing arbuscular mycorrhizal fungi (AMF) abundance and taxa diversity. We evaluated this possibility at a high elevation site in a two-pronged approach. To test whether cheatgrass changed native AMF communities in ways that affected subsequent native plant growth, we grew cheatgrass and native plants in native soils and then planted native plants into these soils in a greenhouse experiment. We found that cheatgrass-influenced soils did not inhibit native plant growth or AMF sporulation or colonization. To test whether soils in cheatgrass-dominated areas inhibited establishment and growth of native plants, cheatgrass was removed and six seeding combinations were applied. We found that 14.02 ±  seedlings · m⁻² established and perennial native plant cover increased fourfold over the three years of this study. Glyphosate reduced cheatgrass cover to less than 5% in the year it was applied but did not facilitate native plant establishment or growth compared with no glyphosate. We conclude that cheatgrass influence on the soil community does not appear to contribute to its invasion success in these high elevation soils. It appears that once cheatgrass is controlled on sites with sufficient native plant abundance, there may be few lingering effects to inhibit the natural reestablishment of native plant communities.     

凤头鸭胚性反转建立及性别候选基因的表达

试验通过对鸭胚注射芳香化酶抑制剂(AI)和β-雌二醇(E2)构建性反转模型,观察其性腺外观形态变化,并荧光定量检测雌性基因P450arom、FOXL2、SF-1和雄性基因DMRT1、SOX9、AMH等6个基因在性反转和正常鸭胚中的表达情况。结果显示:芳香化酶抑制剂能促进公鸭性腺发育,母鸭表现雄化;雌二醇能促进母鸭性腺分化,公鸭表现雌化。DMRT1、SOX9、AMH表达趋势相似,AI促进基因表达使胚胎雄化;E2抑制基因表达使胚胎雌化。P450arom、FOXL2、SF-1在AI组中被抑制使胚胎雄化,在E2组中得到促进发生雌化。该研究结果为研究鸭胚性反转机制奠定理论基础。     

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.     

Enriched Topographic Microsites for Improved Native Grass and Forb Establishment in Reclamation

Low seed germination and seedling establishment are the greatest challenges for revegetation success. Topographic microsites are known to enhance seed germination and seedling establishment due to their unique soil properties and provision of shelter from elements and herbivores; soil amendments can supply organic matter and nutrients for plant establishment and growth when limited. We investigated the effect of three topographic microsites and six soil amendments and their additive effects on three disturbed grasslands in central and southern Alberta, Canada. Treatments were topographic microsites of mounds, pits, and flats, with and without amendments (erosion control blanket, hay, straw, manure, hydrogel, control) and were seeded with four native grasses and three native forb species. Seedling emergence and survival and soil temperature and water content were assessed over two seasons and plant cover over three seasons. The effect of microsites and amendments was not additive. The addition of erosion control blanket, hay, and straw to flat sites was just as productive as on topographic microsites. These amendments increased grass and forb emergence and buffered soil temperature. Mounds increased first year forb emergence and reduced over winter survival rates for grasses and forbs. Pits were not beneficial for revegetation. The effect of topographic microsites and amendments was influenced by site conditions.     

Response of Bluebunch Wheatgrass and Medusahead to Defoliation

Our objective was to determine the short-term response of bluebunch wheatgrass and medusahead to defoliation of wheatgrass designed to stimulate regrowth through tillering. We hypothesized that defoliating bluebunch wheatgrass by 20% at the 3 to 3.5 leaf stage followed by a 50% defoliation at peak standing crop would increase its tillering and biomass production. Consequently, we expected a reduction of the density and biomass of medusahead over that of bluebunch wheatgrass defoliated 50% at peak standing crop. Treatments included four initial medusahead densities (200, 333, 444, 600 plants · m^-2) created by hand-pulling and three defoliation regimes factorially arranged (12 treatment combinations) in a randomized complete-block design and replicated four times at two sites. In 2006 and 2007, defoliation was accomplished by hand-clipping bluebunch wheatgrass 1) by 50% once at peak standing crop (late June); 2) by 20% at the 3 to 3.5 leaf stage, then again to 50% at peak standing crop (mid May, late June); or 3) plants were not clipped. Density was sampled in 2006 and 2007, and biomass was harvested only at Star Mountain (near Riverside, Oregon) in 2007 because Warm Springs (near Drewsey, Oregon) was burned by a wildfire before final 2007 data could be collected. In 2006, no treatments applied at either site detectably altered the number of tillers produced by bluebunch wheatgrass nor did they affect bluebunch wheatgrass density or biomass in 2007 at Star Mountain. Changes in medusahead density were not detected in 2006, but this annual invasive grass increased in density and biomass in 2007 at Star Mountain in plots receiving two defoliations. The relatively short growing period caused by summer drought and the relative intolerance of bluebunch wheatgrass to grazing make the twice-over grazing an unlikely practice for arid rangelands in the western United States. In fact, it could possibly increase the risk of annual grass invasion.     

朱鹮铜绿假单胞菌的分离与初步鉴定

从发病死亡朱鹮肝、脾中分离出一株革兰阴性杆菌,经生物学特性试验和生理生化试验鉴定为铜绿假单胞菌.该菌对小鼠有很强的致病性,药物敏感性试验对氯霉素、氧氟沙星、环丙沙星、氧哌嗪青霉素、氟哌酸等抗菌药物高度敏感;对先锋噻肟、氨苄青霉素、复方新诺明等抗菌药物有耐药性.     

朱鹮引种繁殖试验研究

为了建立不同地区朱种群和加快繁殖 ,2 0 0 2年从洋县引种朱 6 0只到秦岭北麓 ,用人工孵化育雏和亲鸟自然孵化育雏相结合的方法 ,并加强幼鸟管理 ,对其中 14对繁殖朱进行了 2年观察研究。结果显示当年产卵 45枚 ,受精卵 35枚 ,受精率 77.78%,出雏 32只 ,成活2 6只 ,成活率 81.2 5%(2 6 / 32 )。 2 0 0 3年产卵 46枚 ,受精卵 40枚 ,受精率 86 .95%,出雏 35只 ,成活 34只 ,成活率 97.1%(34 / 35)。其中 ,2 0 0 2 ,2 0 0 3年亲鸟自然孵化 ,受精率分别为88.89%和 10 0 %,成活率均为 10 0 %,亲鸟自然孵化育雏优于人工孵化育雏     

Establishment of Native Species in Soils From Russian Knapweed (Acroptilon Repens) Invasions

Russian knapweed (Acroptilon repens [L.] DC.), an exotic perennial forb, has invaded many native ecosystems in western North America. Russian knapweed's success is attributed to allelopathy, extensive tap rooting, zinc accumulation in soils, and a lack of North American predators. Revegetation following chemical control slows exotic reestablishment, but the impacts of Russian knapweed-invaded soils on the establishment of native forbs and shrubs have not been determined. In a greenhouse experiment, we monitored the establishment of two native forbs, Indian blanketflower (Gaillardia aristata Pursh) and purple prairie clover (Dalea purpurea Vent.) and two native shrubs, winterfat (Krascheninnikovia lanata [Pursh] A.D.J. Meeuse & Smit syn. Ceratoides lanata) and Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis [Hook.] Nutt.) in soils obtained from three Russian knapweed invasions and adjacent noninvaded areas. We analyzed soils collected near Greybull and Riverton, Wyoming, and Greeley, Colorado, for cation exchange capacity, organic matter, electroconductivity, pH, and total nitrogen, carbon, and plant-available potassium, zinc, manganese, copper, and phosphate. We documented seedling emergence of the four natives and Russian knapweed every two days for 14–17 weeks, harvested seedlings biweekly to assess their growth, and determined their zinc accumulation. All species established in invaded soil and seedlings were larger in invaded than in noninvaded soils. Invaded rangeland soils had greater organic matter (8.6% and 1.1% in invaded vs. 2.5% and 0.4% in noninvaded soils) and lower pH (7.4 in invaded versus 8.0 noninvaded soils). Zinc concentrations in invaded soils (from 0.15 to 6.56 mg · kg^-1) were not high enough to limit plant growth. Reports that Russian knapweed is a hyper-accumulator of zinc are not supported by our seedling data, which suggests that previously invaded soils may not limit native seedlings.     

朱鹮低致病性禽流感病毒的分离与鉴定

为了掌握朱鹮禽流感病毒流行情况,利用鸡胚分离方法从病死朱鹮脑组织标本中分离出禽流感病毒毒株,并将所分离的病毒进行血凝试验、血凝抑制试验、鸡胚最小致死量平均死亡时间(MDT)、半数致死量(LD50)及1日龄鸡脑内接种致病指数(ICPI)试验.结果表明,所分离的病毒均能够凝集鸡、肉鸭、绵羊、山羊、猪、人、兔等的红细胞,且这...     

朱鹮种群现状及自然迁移规律

从就地保护、易地保护、再引入三方面,系统总结了1981～2008年间朱鹮拯救与保护工作取得的主要成就,并对野生朱鹮种群自然迁移规律进行了系统研究,提出了野生朱鹮种群自然迁移与季节变化密切相关,并针对迁移后的种群保护工作出现的新问题,提出了建议和保护对策。     

Relationship Between Seed Mass and Young-Seedling Growth and Morphology Among Nine Bluebunch Wheatgrass Populations

To better match plant materials to ecological sites for the purpose of rangeland seedling establishment, we examined the relationship between seed size and growth and morphological traits in young seedlings of bluebunch wheatgrass (BBWG) (Pseudoroegneria spicata [Pursh.] Á. Löve), a perennial Triticeae bunchgrass native to the Intermountain West. Traits examined included onset of germination, seedling biomass traits, and seedling surface-area traits. We grew seeds of nine BBWG populations that varied for seed size and were produced in a common environment under 2 contrasting d/n temperature regimes (20/15°C; 10/5°C). Lighter-seeded populations germinated and initiated shoots earlier. Heavier-seeded populations displayed high levels of biomass-related traits (e.g., shoot and root biomass and shoot length), while lighter-seeded populations displayed high levels of surface area ? related traits (e.g., specific leaf area and specific root length [SRL]). Correlations between seed size and young-seedling traits were mostly similar under the two temperature regimes. However, root length ? related traits showed more positive correlations with seed size under the low-temperature regime, which is more similar to actual field-emergence conditions during early spring. P-24, a light-seeded population, originated from the most arid site and exhibited the highest SRL at low temperature, while T-17t, a heavy-seeded population, originated from the most mesic site and exhibited moderate SRL. Three populations used for rangeland revegetation, “Whitmar,” “Goldar,” and Anatone Germplasm, all exhibited low seed mass and high SRL. However, only Anatone displayed high root-to-shoot length ratio under both temperature regimes, perhaps explaining its wide and successful use in rangeland seedings.     

一例朱鹮雏鸟皮下气肿的诊治

动物皮下气肿成因复杂,鸟类(禽类)的皮下气肿常见于体内气囊破裂所致。德清县珍稀动物繁育研究中心2012年首次出现了1例人工饲养的朱鹮雏鸟在15日龄时发生皮下气肿。该气肿位于右侧大腿处,内部充气,气泡内未见其他病变。根据其临床症状,推测可能是由于患雏与其他雏鸟嬉戏打斗过度的充气,或受到撞击等原因使气囊破裂。诊断为右侧腹或后胸气囊破裂,引发皮下气肿。鉴于临床上穿刺排气效果不显著,以及开创排气易引起细菌感染等因素,本病例采用了自然恢复的治疗方式,将患雏转入安静环境,避免外界干扰,加强防护,减少剧烈运动,实行隔离饲养等措施,15日后气肿变小,25日后气肿消失。该病例的诊治及病因的推测,为珍稀鸟类临床上该病的防治提供了方法。