Morphological and physiological responses of the invasive weed Isatis tinctoria to contrasting light, soil-nitrogen and water   总被引：1，自引：0，他引：1  

T A MONACO  D A JOHNSON  & J E CREECH† 《Weed Research》2005,45(6):460-466

We evaluated the morphological and physiological responses to contrasting above- and below-ground resources for the invasive weed, Isatis tinctoria L. (dyer's woad). Plants were grown under low and high levels of light [shade (50% of ambient) and full sun], soil water (50 and 100 mL day⁻¹), and soil nitrogen (N) (0 and 20 mg N kg⁻¹ soil) in 8 L pots in 63 day glasshouse experiments conducted during winter and spring. Soil-N enrichment did not increase any of the growth variables (shoot and root dry mass, shoot:root ratio, leaf area, and specific leaf area) or physiological variables (stomatal conductance and ¹³C discrimination) in either experiment. The absence of plasticity in response to changes in soil-N supply suggests that I. tinctoria may survive and persist in nutrient-poor conditions by having low-N requirements, low-N productivity, or both. In contrast, plants compensated for shaded conditions by altering leaf area, specific leaf area, and shoot:root ratio to improve light capture. We discuss the potential mechanisms whereby response to these variable resources may be associated with a series of adaptations that favour the ability to tolerate and colonize harsh, nutrient-poor conditions, as well as invade shaded and undisturbed sites.  相似文献   

RADIOGRAPHIC SENSITIVITY AND NEGATIVE PREDICTIVE VALUE FOR ACUTE CANINE SPINAL TRAUMA     

JENNIFER KINNS  WILFRIED MAI  GABRIELA SEILER  ALLISON ZWINGENBERGER  VICTORIA JOHNSON  ANA CÁCERES  ALEJANDRO VALDÉS-MARTÍNEZ  TOBIAS SCHWARZ 《Veterinary radiology & ultrasound》2006,47(6):563-570

The objectives of this study were to establish the sensitivity and negative predictive value of radiography for acute spinal osseous lesions in the canine trauma patient, and to evaluate the interobserver variability in radiographic assessment of the spine in traumatized dogs. This was a retrospective multiple observer blinded study. The study population included 30 canine patients that presented following acute trauma, with clinical signs attributable to the spinal column. Radiography and computed tomography (CT) were performed in all cases. Radiographic interpretation was performed independently by four observers with different experience levels who were blinded to clinical information (other than trauma) and the CT results. CT studies were interpreted by a further three radiologists who formed a consensus opinion on the presence of specific osseous lesions. Using the CT results as a gold standard, the sensitivities and negative predictive values of radiography for specific osseous lesions were calculated. Interobserver agreement was also evaluated. Radiography was found to have only a moderate sensitivity for fractures (72%) and subluxations (77.5%). Low negative predictive values were found for the presence of vertebral canal narrowing (58%) and fracture fragments within the vertebral canal (51%). Interobserver agreement was only moderate to fair for most lesion types. In conclusion, radiography cannot be used to reliably rule out potentially unstable acute vertebral lesions in the canine trauma patient, and further imaging is therefore often indicated in the patient with a high risk of such injuries.  相似文献   

INTRACRANIAL SUBARACHNOID HEMORRHAGE FOLLOWING LUMBAR MYELOGRAPHY IN TWO DOGS     

REBECCA A. PACKER  ROBERT L. BERGMAN  JOAN R. COATES  STEPHANIE C. ESSMAN  KEVIN WEIS  DENNIS P. O''BRIEN  GAYLE C. JOHNSON 《Veterinary radiology & ultrasound》2007,48(4):323-327

Intracranial subarachnoid hemorrhage is a rare but serious complication of lumbar puncture in humans. Possible sequelae include increased intracranial pressure, cerebral vasospasm, or mass effect, which can result in dysfunction or brain herniation. We describe two dogs that developed intracranial subarachnoid hemorrhage following lumbar myelography. In both dogs, myelography was performed by lumbar injection of iohexol (Omnipaque). Both the dogs underwent uneventful ventral decompressive surgery for disk herniation; however, the dogs failed to recover consciousness or spontaneous respiration following anesthesia. Neurologic assessment in both dogs postoperatively suggested loss of brain stem function, and the dogs were euthanized. There was diffuse subarachnoid hemorrhage and leptomeningeal hemorrhage throughout the entire length of the spinal cord, brain stem, and ventrum of brain. No evidence of infectious or inflammatory etiology was identified. The diagnosis for cause of brain death was acute subarachnoid hemorrhage. Our findings suggest that fatal subarachnoid hemorrhage is a potential complication of lumbar myelography in dogs. The cause of subarachnoid hemorrhage is not known, but may be due to traumatic lumbar tap or idiosyncratic response to contrast medium. Subsequent brain death may be a result of mass effect and increased intracranial pressure, cerebral vasospasm, or interaction between subarachnoid hemorrhage and contrast medium.  相似文献   

Onset of immunity in salmonid fry vaccinated by direct immersion in Vibrio anguillarum and Yersinia ruckeri bacterins   总被引：3，自引：0，他引：3  

K. A. JOHNSON  J. K. FLYNN  D. F. AMEND 《Journal of fish diseases》1982,5(3):197-205

Abstract. The fry of several salmonid species were vaccinated by direct immersion in either Yersinia ruckeri or Vibrio anguillarum bacterin and the level of protective immunity was determined by the survival of fish after bath challenge with virulent organisms. The immersion time for effective vaccination was obtained within 5 s and protective immunity was demonstrated within 5 days at 18°C and within 10 days at 10°C. The minimum size at which maximum protective immunity occurred was between 1.0 and 2.5 g. Immunity appeared to be a function of size and not age, but differences in response among several species were indicated. In fish under 1.0 g, the level of protective immunity could be increased using a more concentrated bacterin. The results were similar with both bacterins.  相似文献   

Regional Economic Diversity and Diversification     

PAUL B. SIEGEL  THOMAS G. JOHNSON  JEFFREY ALWANG 《Growth and change》1995,26(2):261-284

ABSTRACT Regional scientists have long attempted to develop meaningful definitions and measures of economic diversity and diversification, and to establish functional relationships between diversity, diversification, and economic performance. The multiplicity of definitions and measures explains, in part, the confusion about these relationships. A framework that sorts out the overlaps, contradictions, and gaps of the various definitions and measures IS needed. Such a framework would explicitly address the question, “What is the relationship between a region's changing economic structure and performance?” In this paper it is suggested that an input-output model that incorporates elements of portfolio theory be used as the integrating framework for analysis.  相似文献   

On biochemical origins and optical activity     

FOX SW  JOHNSON JE 《Science (New York, N.Y.)》1956,124(3228):923-925

  相似文献   

Forage production by two Lotus species as influenced by companion grass species     

A. HOPKINS  T. M. MARTYN  R. H JOHNSON  R. D. SHELDRICK  R. H. LAVENDER 《Grass and Forage Science》1996,51(4):343-349

A small-plot experiment was carried out with grass-lotus (Lotus spp.) swards on a lowland (185 m) clay-soil site in S-W England. Two species of lotus (Lotus corniculatus cv. Leo and L. pedunculatus, syn, L. uliginosus, cv. Maku) were each sown at 10 kg seed ha^?1 with lour grass species each at two grass-seed rates: Festuca pratensis at 6 or 3 kg ha^?1 and Phleum pratense, Agrostis capillaris and Poa pratensis at 4 or 2 kg ha^?1. Assessments were made over three harvest years (1992–94). during which no fertilizers were applied. Mean total herbage dry matter (DM) harvested from cv. Leo swards was 90 t ha^?1 in year 1, 8–9 t ha^?1 in year 2 and 4 0 t ha^?1 in year 3. and from cv. Maku swards 6–6 t ha^?1 in year 1. 8–9 t ha^?1 in year 2 and 3–9 t ha^?1 in year 3. Highest three-year mean total yields were with F. pratensis as the companion grass (7–4 t ha^?1 year^?1), followed by Phleum pratense (7–0 t ha^?1), A. capillaris (6–9 t ha^?1) and Poa pratensis (6–2 t ha^?1). The lower grass-seed rate resulted in a greater proportion of lotus in the total harvested DM in year I. The higher grass-seed rate resulted in higher yields from F. pratensis swards in year 1, but there were no significant effects for other species or in subsequent years. Lotus as a proportion of harvested DM declined from about 70% in year 1 to about 20% in year 3. The mean DM yield of lotus herbage in years 1, 2 and 3, respectively, was 5–5, 2–8 and 0–8 t ha^?1 from cv. Leo swards, and 4–0, 3–3 and 0–8 t ha^?1 from cv. Maku swards. Lotus herbage was of higher digestibility from cv. Leo [digestible organic matter (DOM) of 661 g kg^?1 of lotus DM] compared with cv. Maku (551 g kg^?1 DM). Mean N content of lotus herbage was 35 g N kg^?1 DM. Digestibility of companion grass herbage was highest for Phleum pratense (557 g kg^?1 DM) and lowest for A. capillaris (493 g kg^?1 DM). It is concluded that lotus may be an alternative legume to white clover for low-input, low-fertility situations. However, further research is needed to evaluate its performance on different sites and under different management regimes, particularly grazing, and to overcome the apparent problems of its persistence.  相似文献   

Variation in cold tolerance in Festuca rubra L.     

S. McHUGH†  M. O. HUMPHREYS‡  T. McNEILLY  M. S  JOHNSON 《Grass and Forage Science》1988,43(3):305-312

A laboratory assessment was made of cold tolerance in seven cultivars and one natural population of red fescue, overwintered at lowland (30 m a.s.I.) or an upland (300 m a.s.l.) site.
After 5 months overwintering, plants were exposed under laboratory conditions to seven freezing temperatures, –7, –9, – 10, – 11, – 12, – 13 and – 15°C and + 2°C as control. Thawed tillers were grown in soil in glasshouse, and tiller survival and growth recorded after 28 days. Cold tolerance was estimated using LT50 values.
Tiller mortality increased with decreasing freezing temperature, with almost all tillers surviving at – 7°C and almost all dying at – 15°C. Cold hardening at the overwintering site markedly affected survival, plants overwintered at the upland site having significantly greater survival than those overwintered at the lowland site. All samples were affected to similar extent by overwintering site. The samples Aber Valley, Hawk, Merlin, Polar, and Dawson were significantly more cold tolerant than Jupiter, S59, and Highlight. Tiller production data closely resembled those for tiller survival.
For upland situations, eultivars or natural populations other than the currently recommended S59 have better cold tolerance, and may provide useful genetic resources for breeding cultivars for uplands use.  相似文献   

CONTRAST-ENHANCED COMPUTED TOMOGRAPHY AS A PREOPERATIVE INDICATOR OF VASCULAR INVASION FROM ADRENAL MASSES IN DOGS     

RYAN M. SCHULTZ  ERIK R. WISNER  ERIC G. JOHNSON  JENNIFER S. MACLEOD 《Veterinary radiology & ultrasound》2009,50(6):625-629

The purpose of this study was to determine if contrast-enhanced computed tomography (CT) accurately reflected vascular luminal invasion by adrenal masses in dogs. Medical records of 15 dogs with 17 adrenal masses that underwent preoperative CT imaging were reviewed. Presence or absence of vascular invasion was confirmed by surgery or necropsy/histology. Vascular invasion was identified correctly using contrast-enhanced CT in 11/12 dogs. The sensitivity and specificity of contrast-enhanced CT for vascular invasion compared with surgery or necropsy was 92% and 100%, respectively. The positive predictive value and negative predictive value of contrast-enhanced CT was 100% and 90%, respectively. The accuracy was 95%. In one dog, invasion of the phrenicoabdominal vein was not identified on CT images. Six of eight masses with vascular invasion where a histologic diagnosis was obtained were malignant. Four of four pheochromocytomas invaded adjacent vasculature. Contrast-enhanced CT provided accurate preoperative assessment of adrenal masses. Vascular invasion by adrenal masses in this study occurred by way of the lumen of the phrenicoabdominal vein with subsequent intraluminal extension into other veins, rather than by erosion through vessel walls.  相似文献   

Behaviour of adult Pacific lamprey in near‐field flow and fishway design experiments     

M. L. KEEFER  S. R. LEE  E. L. JOHNSON  M. L. MOSER 《Fisheries Management and Ecology》2011,18(3):177-189

Abstract An experimental fishway was used to examine adult Pacific lamprey, Lampetra tridentata (Gairdner), behaviour in a series of attraction and passage‐performance tests. Among all experiments, lamprey oriented to the fishway floor and walls and were attracted to both ambient and concentrated flow. When confronted with high‐velocity areas (vertical‐slot and submerged‐orifice weirs), many lamprey failed to pass upstream. However, lamprey were able to find and take advantage of low‐velocity refuges when they were provided. Lamprey climbed shallow‐ and steep‐angled ramps when attraction cues were sufficient and other passage routes were restricted. The combined results demonstrated the passage challenges that fishways designed and operated for salmonids present to non‐salmonid species. They also highlight the importance of evaluating trade‐offs between fishway attraction and passage efficiency. The experiments were integrated with tagging studies and development of lamprey‐specific passage structures, a research combination that provided an effective template for fishway performance evaluations.  相似文献