呼伦贝尔草原野生牧草青贮中优良乳酸菌的分离及鉴定

本研究对呼伦贝尔草原牧草青贮饲料中的乳酸菌进行了分离、鉴定,旨为筛选出优良乳酸菌菌株。以4个地区不同群落牧草的青贮饲料为试验材料,并采用传统微生物学鉴定方法及16S rRNA序列分析对分离得到的乳酸菌菌株进行了鉴定。菌株DME53为草乳杆菌,DMG108为干酪乳杆菌,DMC80为植物乳杆菌,DMG138为短乳杆菌,DMG139为戊糖片球菌;其中菌株DMG138为异型发酵乳酸菌,其余4株菌均为同型发酵乳酸菌。除DMG139在40和45 ℃下生长微弱外,其余菌株均在5~45 ℃不同温度条件下, 3.0%和6.5% NaCl培养液中良好生长。除菌株DME53在pH 3.0下不能生长外,其余菌株均在pH 3.0~8.0条件下良好生长或微弱生长。菌株DMC80具有产酸能力较强、发酵速率较快、耐酸、耐低温等特性,可作为制备适用于呼伦贝尔地区青贮饲料菌制剂的优良菌株。     

The invasive weed Ventenata dubia is a host of Barley yellow dwarf virus with implications for an endangered grassland habitat

Ventenata dubia (African wiregrass), a winter annual weed, is a non‐native species invading grasslands, rangelands and pastures throughout the USA. Limited information is available on its suitability as a host to pathogens and insects in its invaded range. The barley/cereal yellow dwarf virus (B/CYDV) complex occurs ubiquitously in Poaceae species. In non‐managed grasslands, BYDV infection influences competitive dynamics between native and invasive grasses and facilitates invasion by non‐native annual weeds. The Palouse prairie of south‐eastern Washington and northern Idaho, USA, is an endangered ecosystem. Surveys of V. dubia in Palouse prairie and neighbouring Conservation Reserve Program (CRP) habitats were conducted to determine whether B/CYDV viral species are present. Laboratory tests examined the suitability of V. dubia to host BYDV‐PAV and serve as an inoculum source. Plant growth and weight parameters were measured to gauge the impact of BYDV‐PAV on V. dubia. Infection of V. dubia in Palouse prairie and CRP habitats with two species of BYDV, PAV and SGV, was detected for the first time. The ability of BYDV‐PAV to infect V. dubia in the laboratory and transmission from infected V. dubia to barley were demonstrated. BYDV‐PAV‐infected V. dubia showed reductions in plant height, number of leaves and tillers per plant, and above‐ground dry weight, suggesting that V. dubia is sensitive to BYDV. Results demonstrate that V. dubia is a host to BYDV and may serve as a virus inoculum source with potential implications for its management, competitive dynamics between invasive and native grasses and future conservation of endangered grasslands.     

New experimental hosts of Barley yellow dwarf virus among wild grasses,with implications for grassland habitats

Barley yellow dwarf virus (BYDV), an economically important virus, infects small grain cereal crops and over 150 other Poaceae species. BYDV infection plays an important role in competition among grasses in non‐managed systems, but many grasses remain unexamined as potential BYDV hosts. This study examined grass species that have not been reported as BYDV hosts but are commonly encountered in non‐managed grasslands throughout the United States and Canada. Laboratory inoculations with BYDV‐PAV using the aphid vector Rhopalosiphum padi were performed to examine the ability of 13 grass species and barley to be infected with the virus; eight of the grass species were not documented previously as virus hosts. Serological and molecular assays were used to confirm BYDV‐PAV infection. Plant height, number of leaves, number of tillers and weight were recorded to evaluate susceptibility or sensitivity to BYDV. Infection with BYDV was experimentally achieved for the first time on Achnatherum lettermanii, Achnatherum occidentale, Achnatherum thurberianum, Danthonia intermedia, Poa fendleriana, Sporobolus airoides and Sporobolus cryptandrus, but not on Alopecurus pratensis and Elymus wawawaiensis. Infection was confirmed in Bromus inermis, Elymus elymoides, Poa bulbosa, Poa secunda and Hordeum vulgare, which served as controls. BYDV infection caused reductions in plant height on P. bulbosa and P. fendleriana. BYDV‐infected P. secunda had more leaves per plant compared to healthy plants of the same species. BYDV‐infected A. lettermanii exhibited reduced dry weight in both below‐ground and above‐ground tissue. These findings have implications for the management and conservation of grassland habitats.     

The role of community composition in grassland response to two methods of exotic forb removal

Invasive plants can seriously threaten biodiversity and ecosystem function. Thus, controlling the abundance and mitigating the deleterious effects of invasive plants is imperative. The effectiveness of removal methods could vary based on potential damage to non‐target species and on the ecological context of invasion. For example, species‐poor communities might benefit disproportionately from invasive removal because they tend to be more heavily invaded than species‐rich communities. In this study, we tested the efficacy of two common methods of invasive plant control, hand removal and 2,4‐D herbicide application, against the invasive forb, Galium verum. We further tested whether the community response to G. verum removal varied across communities that differed in native grass richness (one, three or six species) and composition. Grass diversity did not interact with G. verum removal to influence any response. Instead, hand removal and herbicide application each reduced G. verum stem density by >50% relative to controls. Furthermore, hand removal of G. verum increased species richness by 25% relative to controls and herbicide‐sprayed plots. Despite this benefit, hand removal is labour‐intensive and impractical for large areas. These results also suggest that applying herbicide may control G. verum spread without substantially reducing forb diversity in invaded tallgrass prairie. Thus, herbicide application may be most suitable for grasslands with low native forb diversity, especially in managed grasslands and pastures where maintaining native forb diversity is a lower priority than maintaining high grass productivity.     

COMPUTED TOMOGRAPHIC FEATURES OF INCISOR PSEUDO‐ODONTOMAS IN PRAIRIE DOGS (CYNOMYS LUDOVICIANUS)

Maxillary incisor pseudo‐odontomas are common in pet prairie dogs and can cause progressive respiratory obstruction, while mandibular pseudo‐odontomas are rarely clinically significant. The aim of this retrospective cross‐sectional study was to describe CT features of maxillary and mandibular incisor pseudo‐odontomas vs. normal incisors in a group of pet prairie dogs. All pet prairie dogs with head CT scans acquired during the period of 2013–2015 were included. A veterinary radiologist who was aware of final diagnosis reviewed CT scans and recorded qualitative features of affected and normal incisors. Mean density values for the pulp cavity and palatal and buccal dentin were also recorded. A total of 16 prairie dogs were sampled (12 normal maxillary incisors, 20 confirmed maxillary incisor pseudo‐odontomas, 20 normal mandibular incisors, 12 presumed mandibular incisor pseudo‐odontomas). Maxillary incisors with confirmed pseudo‐odontomas had a significantly hyperattenuating pulp and dentin in the reserve crown and apical zone, when compared to normal maxillary incisors. Pseudo‐odontomas appeared as enlargements of the apical zone with a globular/multilobular hyperattenuating mass formation haphazardly arranged, encroaching on midline and growing caudally and ventrally. Presumed mandibular incisor pseudo‐odontomas had similar CT characteristics. In 60% of prairie dogs with maxillary incisor pseudo‐odontomas, the hard palate was deformed and the mass bulged into the oral cavity causing loss of the palatine bone. The common nasal meatus was partially or totally obliterated in 81.8% of prairie dogs with maxillary pseudo‐odontomas. Findings supported the use of CT for characterizing extent of involvement and surgical planning in prairie dogs with pseudo‐odontomas.     

黄土高原典型草原区草地土壤种子库的动态分析

采用野外调查取样和室内试验相结合的方法,研究了黄土高原典型草原区草地土壤种子库的物种组成、密度、时空格局和物种多样性等特征。结果表明,（1）土壤种子库中共统计到37个物种,隶属于16科,其中禾本科、菊科、唇形科、豆科和毛茛科的植物占优势。（2）从返青期到枯黄期,种子库中豆科、禾本科、堇菜科所占比例呈下降趋势,唇形科和菊科所占比例明显提高,种子库的密度也显著提高。（3）种子库中种子数量在垂直分布上呈现出由表层土壤向深层逐层减少的变化规律;在水平分布上的变化规律为：封禁〉放牧;阴坡〉阳坡;下坡〉中坡〉上坡。（4）封禁地土壤种子库中的Margalef丰富度和Shannon--Wienner指数都高于放牧地,Pielou均匀性指数低于放牧地。从返青期到枯黄期,封禁地和放牧地土壤种子库的Margalef丰富度、ShannonWienner指数、Pielou均匀性指数都呈下降趋势。     

Restoring grassland biodiversity: Sowing low-diversity seed mixtures can lead to rapid favourable changes

We studied the effect of sowing low-diversity seed mixtures (containing 2-3 competitive grass species) on the regeneration of vegetation on croplands previously used as alfalfa fields. In four permanent plots in 10 restored fields (four with alkali and six with loess seed mixture) the cover of flowering plants was recorded and phytomass was measured between 2006 and 2008. We asked three questions: (i) How fast will weedy, short-lived species decrease in abundance during secondary succession enhanced by sowing low-diversity seed mixtures? (ii) Can weeds be suppressed by sowing competitive native grasses, followed up by management by mowing? (iii) Can succession towards the target native grasslands be accelerated by sowing only low-diversity seed mixtures compared to set-aside old field succession? Our results showed that in just two years a vegetation dominated by perennial grasses has developed, which successfully prevented the establishment of weed species. These results suggested that sowing seeds of two or three competitive grass species is an effective tool to eliminate weed domination and to lead towards the restoration of species poor grasslands with grass domination such as alkali grasslands. However, the developed dense perennial grass cover and the accumulated litter may hamper the immigration of specialist species characteristic to reference grasslands. Therefore, the restoration of species-rich grasslands requires the facilitation of the immigration of grassland specialist species by further management (grazing, mowing and/or hay-transport).     

Burning and Climate Interactions Determine Impacts of Grazing on Tallgrass Prairie Systems

Tallgrass prairie may respond differently to prescribed burning and subsequent preferential grazing, termed pyric herbivory, under variable climate conditions. This 6-yr study (2011−2016) compared tallgrass prairie pastures that were subjected to burned and unburned conditions while exposed to grazing under differing climate conditions in the Southern Great Plains of the United States. The study area consisted of six pastures, three burned and three unburned. Each burned pasture was further divided into three patches and subjected to a 3-yr rotational burning cycle. The Enhanced Vegetation Index (EVI) derived from Landsat 7/8 (EVI_LS) and Moderate Resolution Imaging Spectroradiometer (MODIS, EVI_MOD) was used to indicate vegetation production depending on size of pastures. On the basis of EVI_LS, most burned patches (11 of 18) had lesser production (overall difference of 3%) than unburned patches within the same pasture. The differences were larger (13%) in a drought yr (2011) compared with normal (3% in 2013) and wet (<1% in 2015) yrs. The distribution of precipitation controlled EVI_LS for periods during and after grazing. The burned patches tended to have lower EVI_LS during grazing periods than the unburned patches within the same pasture, probably because of selective grazing of newly grown grass in recently burned patches. In contrast, the differences in EVI_LS between during and after grazing periods were mostly (78%) smaller in burned than unburned patches. However, more variations in EVI_LS existed among pasture comparisons due to landscape heterogeneity. Similar results were observed with EVI_MOD. Overall, results demonstrated that pyric herbivory management and climate determine the impacts of grazing on tallgrass prairie systems. The contrasting seasonal forage availabilities in burned and unburned patches, indicated by different seasonality of EVI, also suggests that patch burning might better balance the quantity and quality of the grass available for cattle grazing.