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.     

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.     

蓝茎冰草种子产量与施氮量和密度互作的模型分析

通过3因素5水平二次通用正交旋转组合设计方案,建立回归模型,进行解析、寻优和频数分析。结果表明:各试验因素对蓝茎冰草(Pascopyrum smithii)种子产量影响的大小顺序为施氮量(X₂)>植株密度(X₁)>喷施PP 333(X₃);施氮量与植株密度的互作效应对种子产量的作用为协同效应;同时得出了3因素对种子产量的优化配比方案:植株密度429.4~450×10⁴株/hm²,施氮量160~164.9kg/hm²,喷施PP 333量0.197~0.233 a.i.kg/hm²。     

Short-Term Response of Two Beneficial Invertebrate Groups to Wildfire in an Arid Grassland System,United States

Rangeland invertebrates contribute greatly to biodiversity and provide important services including pollination, pest control, and nutrient cycling. As wildfire frequency increases across these areas of the United States, it is imperative to understand how these disturbances affect beneficial invertebrate communities. We examined bee (Hymenoptera), spider (Araneae), and vegetative communities 1 yr before and 1 yr after a large wildfire swept across an intact grassland in eastern Oregon. Several sites were left unburned after the fire, and a before-after-control-impact study design was used to assess changes within the communities. Fire had no effect on bee or spider abundance, or spider diversity or richness; however, fire significantly increased native bee diversity and richness. In addition, composition of both native bee and spider communities differed significantly between burned and unburned areas 1 yr after the fire. Sheet web spiders (Linyphiidae) and several bee species (primarily large, generalist species) were associated with burned sites. Invasive annual grass and biological soil crust cover decreased significantly in burned sites, but maximum vegetation height and litter cover did not differ significantly among treatments. Forb abundance increased in burned sites; however, species richness of forbs in burned and unburned sites did not differ significantly 1 yr after the fire. Several forbs were indicative of burned areas including non-native species, such as Douglas’ knotweed (Polygonum douglasii) and Russian thistle (Salsola tragus), and native species such as Canadian horseweed (Conyza canadensis), hoary tansyaster (Machaeranthera canescens), and tall willowherb (Epilobium brachycarpum). This study demonstrates that both invertebrate and plant communities show strong short-term responses to wildfire, and our results can be used to inform management of rare habitat and biodiversity in rangelands impacted by wildfire in arid grasslands.     

宁夏盐池干旱风沙区膜荚黄芪种植效益及黄芪栽培技术

2011—2013年,宁夏盐池县科学技术局引进并应用黄芪种植成熟技术,在盐池干旱风沙区扬黄灌区、十六堡旱沙地进行了膜荚黄芪的种植试验,在取得较好经济效益的同时,又结合当地气候和土壤条件总结出了黄芪的栽培技术,以期使膜荚黄芪能够在同类地区推广应用。     

Long-Term Livestock Exclusion in an Arid Grassland Alters Vegetation and Soil

Changes in soil and vegetation due to livestock grazing are occurring in arid lands throughout the world. The most extreme cases result in desertification, which is seen as largely irreversible, because of altered soil properties. To understand better how long-term livestock removal affects soil properties and vegetation, we compared water-infiltration rates, soil bulk density, and perennial grass cover inside and outside a long-term livestock exclosure in an arid grassland site in southeastern Arizona, United States. The site had not been desertified at the time of this study. Exclusion of livestock for 40 yr was associated with lower bulk density and higher water infiltration in both the dry and wet seasons. Perennial grass cover was higher and two native grasses, Eragrostis intermedia and Bouteloua hirsuta were significantly more common (P < 0.05) in the ungrazed area. These findings parallel our results from a desertified site and suggest that changes in soil physical properties associated with long-term livestock removal are not an artifact of desertification and can take place in a system that has remained in a grassland state. Our data suggest that, although significant changes in species composition have occurred, this grassland is relatively resilient to substantial changes in soil physical properties.     

高寒山区旱作条件下细茎冰草生产性能测定

通过3年的测定结果表明,细茎冰草Agropyron trachycaulum cv.Slender在青海东部农业区的高寒山区旱作条件下,可以安全越冬,越冬率为86%～90%,第2和3年的平均干草产量分别为3 856.6,5 386.7 kg/hm2,籽实产量分别为897,1 150 kg/hm2,生育期133～140 d,属中、晚熟多年生优良禾本科牧草品种,适合在海拔为2 750 m左右的旱作条件下种植,具有良好的推广前景.     

牧草、饲料作物生产在三元种植结构生产体系中的作用

由于种植结构不合理 ,直接导致资源浪费 ,二元种植结构本身难以发挥农业生态系统的整体功能 ,更难以适应现代农业可持续发展的要求。而三元种植结构是适应我国当代食物结构的改革 ,发展优质高效农业总体布局的重大举措之一。三元种植结构 ,改变了由农作物生产转变成籽实生产和牧草、饲料作物生产相结合 ,籽实生产也一部分转为饲料用粮生产 ,牧草及饲料作物生产可大大提高转化率和消化率 ,直接为畜牧业提供优质、廉价的饲料资源。通过优质、高效的畜产品转化 ,实现农牧生产的高效率和高效益。培育了新的经济增长点 ,同时增加农业系统中的生物…     

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.     

Soil Moisture Enhancement Techniques Aid Shrub Transplant Success in an Arid Shrubland Restoration

In arid and semi-arid environments, where low and unpredictable rainfall is typical, establishment of perennial vegetation can be enhanced with modest increases in soil moisture. We evaluated methods for promoting shrub transplant establishment. We transplanted approximately 1 000 3-mo-old seedlings in April 2004, 2005, and 2006, using a full-factorial design with combinations of three treatments: addition of mycorrhizae spores to the root zone, addition of a hydrogel to the root zone, and placement of a wood obstruction south of the plant. We planted three shrubs: big sagebrush (Artemisia tridentata Nutt. ssp. tridentate), four wing saltbush (Atriplex canescens [Pursh] Nutt.), and rubber rabbitbrush (Ericameria nauseosa [Pall. ex Pursh] G.L. Nesom & Baird ssp. nauseosa) in a 1.2-ha area. The summer months of 2004 and 2006 were dry, leading to low survivorship (< 1%). With higher rainfall in summer 2005, transplant survivorship was ～18%. For the 2005 transplants, A. tridentata had the highest survivorship after one growing season (31.0%), followed by A. canescens (20.6%) and E. nauseosa (6.9%). Placing a wood obstruction near the plant was significant in the statistical model to describe short-term overall transplant survival and survival of A. tridentata. Placing hydrogel in the root zone also explained short-term overall transplant survival, as well as survival of E. nauseosa. However, by 4.5 yr after transplanting, there was no significant treatment effect on survival. Thus, for transplanting shrub seedlings on arid or semi-arid sites, we recommend some form of resource enhancement technique to increase short-term survival. In this experiment, both the obstruction and hydrogel treatments were effective. We recommend the obstruction treatment since slash is often readily available onsite, has low labor requirements and cost, and it increased transplant survival of A. tridentata, a species of conservation concern; however, other treatments may be appropriate for individual species.     

Restoration of Sagebrush in Crested Wheatgrass Communities: Longer-Term Evaluation in Northern Great Basin

Crested wheatgrass (Agropyron cristatum [L] Gaertm. and Agropyron desertorum [Fisch.] Schult.), an introduced bunchgrass, has been seeded on millions of hectares of sagebrush steppe. It can establish near-monocultures; therefore, reestablishing native vegetation in these communities is often a restoration goal. Efforts to restore native vegetation assemblages by controlling crested wheatgrass and seeding diverse species mixes have largely failed. Restoring sagebrush, largely through planting seedlings, has shown promise in short-term studies but has not been evaluated over longer timeframes. We investigated the reestablishment of Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis [Beetle & A. Young] S.L. Welsh) in crested wheatgrass communities, where it had been broadcast seeded (seeded) or planted as seedlings (planted) across varying levels of crested wheatgrass control with a herbicide (glyphosate) for up to 9 yr post seeding/planting. Planting sagebrush seedlings in crested wheatgrass stands resulted in full recovery of sagebrush density and increasing sagebrush cover over time. Broadcast seeding failed to establish any sagebrush, except at the highest levels of crested wheatgrass control. Reducing crested wheatgrass did not influence density, cover, or size of sagebrush in the planted treatment, and therefore, crested wheatgrass control is probably unnecessary when using sagebrush seedlings. Herbaceous cover and density were generally less in the planted treatment, probably as a result of increased competition from sagebrush. This trade-off between sagebrush and herbaceous vegetation should be considered when developing plans for restoring sagebrush steppe. Our results suggest that planting sagebrush seedlings can increase the compositional and structural diversity in near-monocultures of crested wheatgrass and thereby improve habitat for sagebrush-associated wildlife. Planting native shrub seedlings may be a method to increase diversity in other monotypic stands of introduced grasses.     

Genetic Variation of An Esterase System in Sera of Dogs

Sera from 7 dog families comprising 20 parents with 48 offspring and 70 unrelated dogs of various breeds have been studied with regard to polymorphism of esterases. Isoelectric focusing in Polyacrylamide gels of pH ranges 4.2–4.9 and 4–6 revealed great variation of phenotypes. These appeared as complex band patterns always with more than 8 zones. Treatment with an organophosphorous compound and ions of heavy metals strongly indicate that the majority of zones represent arylesterase (ArE) whereas some of the bands are Cholinesterase. ArE phenotypes in families together with the appearances of band patterns in the 70 unrelated dogs are in agreement with a genetic theory of 1 locus with 5 codominant alleles. These have temporarily been named ArE^D, ArE^H, ArE^K, ArE^Q and ArE^W with ArED being the most anodal phenotype and the others in logical order. The ArE^K and ArE^Q were most common but phenotypes representing the ArE^D, ArE^H and ArE^W alleles were each observed in several animals.     

盐胁迫对NHC牧草IAA、ABA、CaM及NADKase的动态变化

研究NewHy Crested Wheatgrass牧草(NHC)盐胁迫下部分胞间胞内信号分子的变化及部分耐盐机理,将为改良辽宁营口沿海产业基地NaCl型盐碱地奠定基础。以Hoagland培养液培养NHC牧草,3周后对幼苗进行NaCl溶液和土壤盐溶液胁迫处理,并测定吲哚乙酸(IAA)、脱落酸(ABA)、钙调蛋白(CaM)及NAD激酶(NADKase)活性。结果表明：在100、200 mmol/L NaCl盐及土壤盐处理条件下,IAA含量无差异,但比对照极显著升高;其他各生理指标均随浓度升高而极显著升高。由此可见,NHC牧草通过ABA和IAA含量的变化,激活钙信号系统,增加CaM含量,激活NADKase活性,调节细胞代谢活力,从而提高耐盐胁迫能力。NHC牧草耐盐临界浓度分别为土壤盐浓度200 mmol/L、NaCl浓度 300 mmol/L。同样浓度条件下,土壤盐溶液对NHC牧草的伤害比NaCl溶液更大。     

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.     

干旱地区草坪的水分管理

草坪建设是人们对生态环境、休闲健身的要求 ,是生活水准提高的重要标志。在干旱地区建设草坪具有与其它地区所不同的特点和要求 ,主要表现在冷季型草种播种、蒸发强烈、夏季需水量大、有防尘淋洗需水量和冬灌要求。从水量平衡原理出发 ,以节水型草坪建设为目标 ,提出了干旱地区草坪坪床土壤水分平衡模型 ,并根据干旱地区草坪水分管理特点 ,应用坪床土壤水分平衡模型制定了草坪水分管理的一般性策略和不同类型草坪的水分制管理模式。     

黄土高原轮作系统苜蓿土壤磷素变化特征

在长期定位试验的基础上,分析黄土高原旱地轮作系统中苜蓿（Medicago sativa）不同生长年份土壤的无机磷、有机磷形态及微生物磷的变化特征,以期为农牧区牧草有效磷素合理利用及区域管理提供依据。结果表明：种植苜蓿的土壤全磷含量与苜蓿种植年份成反比,连续种植苜蓿年份越长,土壤全磷和速效磷的含量越小。苜蓿土壤中无机磷组分以Ca-P为主,占无机磷总量的74.0%～80.0%,且Ca₁₀-P > Ca₈-P > Ca₂-P。有机磷占全磷总量的23.2%～25.4%,土壤有机磷以中活性有机磷为主,占有机磷总量的78.3%～79.5%。苜蓿的种植年份越长,土壤微生物磷含量越低。土壤微生物磷与土壤全磷、速效磷成极显著相关,故土壤微生物磷可作为土壤供磷能力的指标。     

Demography and dog-human relationships of the dog population in Zimbabwean communal lands

Dogs are Zimbabwe's primary vector for rabies, and the majority live in communal lands (traditional agropastoralist rural areas). In 1994, a household questionnaire survey was conducted to provide baseline data on the demography and dog-human relationships of the dogs in the communal lands. The survey showed that all the dogs were owned, and there was no evidence of a feral population. They were unrestricted and semi-dependent on people. The numbers of dogs per capita varied little in each communal land, resulting in higher dog densities in communal lands with higher human densities, and indicating that people were not intolerant of dogs at higher densities. The population turnover was rapid: the life expectancy of the dogs was 1.1 years, the mean age 2.0 years, and 71.8 per cent died in their first year. The population was heavily skewed towards juveniles, with 40.8 per cent aged less than 12 months. Despite the high juvenile mortality, the population was growing by 6.52 per cent per annum. It was estimated that in 1994 there were 1.36 million dogs in communal lands.     

不同放牧率对草原植物与土壤C、N、P含量的影响

本文研究不同放牧率对草原植物土灌系统中C、N、P含量的影响。结果表明,对照区地上生物量和0～60m土层的总根量显著大于各放牧处理(P＜0.01),而放牧处理间差异不显著(P＞0.05)。对照区和1.33只羊/hm²处理植物的C含量显著大于4只羊/hm²和6.67只羊/hm²,而后两个处理的N、P含量较高。4只羊/hm²处理的C/N和C/P最小。6.67只羊/hm²处理已使根系和根系中的N素明显向表层聚集。对照区0～10cm土层土壤有机C含量显著大于各放牧处理,而各放牧处理间差异则不显著。土壤有机C,N含量与报系生物量成显著正相关。0～10cm土层中无机N在4只羊/hm²处理中最大。土壤微生物量C、P含量在6.67只羊/hm²处理中显著降低,其它处理间差异不显著。其中4只羊和6.67只羊/hm²处理的微生物N含量较高。