Photosynthate distribution patterns in cherrybark oak seedling sprouts     

Lockhart BR  Hodges JD  Gardiner ES  Ezell AW 《Tree physiology》2003,23(16):1137-1146

We used 14C tracers to determine photosynthate distribution in cherrybark oak (Quercus pagoda Raf.) seedling sprouts following release from competing mid-story vegetation. Fall acquisition of labeled photosynthates by seedlings followed expected source-sink patterns, with root and basal stem tissues serving as the primary sinks. Four months after the seedlings had been labeled with 14C, they were clipped to induce sprouting. First-flush stem and leaf tissues of the resulting seedling sprouts were the primary sinks for labeled photosynthates stored in root tissues. Second-flush stem and leaf tissues, and first-flush stem and leaf tissues the following growing season, were not primary sinks for labeled photosynthates stored in root tissues despite the high radioactivity in root tissues. Root tissues appeared to deposit photosynthates in a layering process whereby the last photosynthates stored in new xylem were the first to be depleted during the initiation of a growth flush the following spring. There were more labeled photosynthates in roots of released seedling sprouts compared with non-released seedling sprouts, indicating increased vigor of released seedling sprouts in response to greater light availability. In contrast, stem and source leaf tissues of non-released seedling sprouts contained greater percentages of labeled photosynthates compared with released seedling sprouts, indicating either greater sink strength or poorly developed xylem and phloem pathways that created inefficiencies in distribution to root tissues. The 14C distribution coefficients confirmed the distribution patterns and provided additional information on the important sinks in released and non-released cherrybark oak seedling sprouts.  相似文献   

DIHYDROXY-STEARIC ACID AND VITAMIN K DEFICIENCY     

Lockhart EE  Sherman H  Harris RS 《Science (New York, N.Y.)》1942,96(2502):542-543

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NUTRITIVE VALUE OF THE MEXICAN TORTILLA     

Cravioto RO  Anderson RK  Lockhart EE  DE P Miranda F  Harris RS 《Science (New York, N.Y.)》1945,102(2639):91-93

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Soil quality and financial performance of biodynamic and conventional farms in new zealand   总被引：3，自引：0，他引：3  

Reganold JP  Palmer AS  Lockhart JC  Macgregor AN 《Science (New York, N.Y.)》1993,260(5106):344-349

Biodynamic farming practices and systems show promise in mitigating some of the detrimental effects of chemical-dependent, conventional agriculture on the environment. The physical, biological, and chemical soil properties and economic profitability of adjacent, commercial biodynamic and conventional farms (16 total) in New Zealand were compared. The biodynamic farms in the study had better soil quality than the neighboring conventional farms and were just as financially viable on a per hectare basis.  相似文献   

Preliminary biochemical observations of fishes inhabiting an acidified lake in Ontario,Canada     

W. L. Lockhart  A. Lutz 《Water, air, and soil pollution》1977,7(3):317-332

Blood serum and other tissues of white suckers (Catostomus commersoni) and other species of fish have been examined in a preliminary effort to understand losses of fish from acid lakes. Maturing females of highly acid George Lake failed to show the normal degree of increase in serum Ca over males captured in the same location. Elevated serum Ca was always observed in females, relative to males, from non-acid locations when maturation stages were similar. A number of body tissues were examined to determine whether the distributions of Ca or other elements were altered and the only striking change evident in fish from George Lake was their high Mn content. Bone in particular was examined for N, Na, Mg, P, K, and Ca and no evidence of demineralization was found. Other tests such as hemoglobin indicated that an anticipated adaptive response to asphyxia was absent. Our results indicate that potential mechanisms of fish losses such as asphyxia and starvation are unlikely to have been significant, however, they do not firmly establish any alternate mechanism. As a working hypothesis we suggest that Ca dynamics may limit ovarian development and that absorption of this metal at exchange surfaces may be impaired.  相似文献   

Current and historical inputs of mercury to high-latitude lakes in Canada and to Hudson Bay     

W. L. Lockhart  P. Wilkinson  B. N. Billeck  R. V. Hunt  R. Wagemann  G. J. Brunskill 《Water, air, and soil pollution》1995,80(1-4):603-610

Sediment cores collected from several lakes in northern Canada have been analyzed for mercury and several other chemical contaminants. Sites ranged from the Experimental Lakes Area of northwestern Ontario, north to Cornwallis Island, and west to the southern Yukon. Cores were sliced at sites of collection and individual slices were freeze dried and analyzed for Pb-210 and Cs-137 to estimate average time intervals of deposition. The earliest date estimated by Pb-210 was about 1850, and mercury concentrations in some lakes were clearly increasing before then, assuming no vertical movements of mercury within the sediments. Extrapolation of dates downward to deeper slices, assuming a constant sedimentation rate, indicated that in some lakes mercury inputs increased slowly even in the 1500's, more rapidly after 1750, and more rapidly yet over the current century. These increases are interpreted as increased fluxes of mercury to the lakes as a result of long-range transport of atmospheric mercury, since there are no local industrial sources of mercury. Slices taken near the bottom of a core are taken to estimate the geological component while elevations in excess of that in surface slices are taken to represent contamination from fallout. This partitioning suggests that sediments in the eastern Northwest Territories are dominated by pollution, while those from the western Northwest Territories are influenced more by their geological settings. Two cores from Hudson Bay suggest that mercury is increasing there too, but has not yet exceeded geological sources. Mercury shows little or no tendency to decline in the most recent slices; indicating that inputs of mercury remain at or near their historical maxima. Given relatively high and continuing inputs of mercury to northern lakes it seems likely that some portion of that mercury may find its way into the food chain, hence the long-term prospect is for increasing levels of mercury in northern fish.  相似文献   

Collection of Atomic Bomb Debris from the Atmosphere by Impaction on Screens     

Blifford IH  Lockhart LB  Baus RA 《Science (New York, N.Y.)》1956,123(3208):1120-1121

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Tree species exhibit complex patterns of distribution in bottomland hardwood forests     

Luben D. Dimov  Jim L. Chambers  Brian Roy Lockhart 《Annals of Forest Science》2013,70(8):813-823

?Context

Understanding tree interactions requires an insight into their spatial distribution.

?Aims

We looked for presence and extent of tree intraspecific spatial point pattern (random, aggregated, or overdispersed) and interspecific spatial point pattern (independent, aggregated, or segregated).

?Methods

We established twelve 0.64-ha plots in natural bottomland hardwood stands in the southeastern USA.

?Results

Spatial point pattern analyses (Ripley’s K, L, and L ₁₂) indicated that, when species were combined, trees were frequently aggregated and less commonly overdispersed. Plots with larger trees were more likely to exhibit overdispersion, confirming a shift to this pattern as trees grow. The intraspecific pattern of cherrybark oak and water oak was either aggregated or random. Sweetgum was aggregated on all plots and always at smaller distances (less than 5 m) than the two oak species. Intraspecific overdispersion was very rare. Interspecific segregation among the two oak species was more commonly observed (six plots) than aggregation (one plot). Cherrybark oak and sweetgum were segregated at some scale on seven of the 12 plots and aggregated on only two plots.

?Conclusion

The results from the analyses suggest that strong interspecific competition may result in segregation of trees from different species, while weaker intraspecific competition may lead to aggregations of conspecifics.  相似文献   

Détection du sugarcane bacilliform badnavirus au Maroc par le test du Western blotting     

Nadif  M. Elyachioui  I. Elhadrami  B.E.L. Lockhart 《EPPO Bulletin》1999,29(1-2):179-181

Depuis la découverte du sugarcane bacilliform badnavirus (SCBV) au Maroc, plusieurs études ont été réalisées au niveau du Centre Technique des Cultures Sucrières en collaboration avec l'Université de Minnesota (US) afin d'améliorer son niveau de détection et renforcer les mesures de contrôle aussi bien au niveau de la grande culture qu'au niveau de la quarantaine. L'étude présentée dans cet article montre la possibilité de détecter le SCBV par la technique du Western blotting et permet aussi la comparaison entre les résultats de cette technique et ceux de l'ELISA.  相似文献   

Temporal aspects of the epidemic of bovine spongiform encephalopathy in Great Britain: individual animal-associated risk factors for the disease     

Stevenson MA  Wilesmith JW  Ryan JB  Morris RS  Lockhart JW  Lin D  Jackson R 《The Veterinary record》2000,147(13):349-354

The objectives of this study were first to determine the cumulative incidence of bovine spongiform encephalopathy (BSE) in the British cattle population from July 1986 to June 1997, secondly, to identify individual animal-associated risk factors that influenced the age of onset of clinical signs in confirmed BSE cases, and, thirdly, to assess the effectiveness of the measures introduced to control BSE during the epidemic. The analyses were based on the population of British cattle at risk, derived from agricultural census data collected between 1986 and 1996, and BSE case data collected up to June 30, 1997. The unit of interest was individual adult cattle recorded on annual agricultural censuses between June 1986 and June 1996. Univariate and multivariate survival analysis techniques were used to characterise the age of onset of clinical signs. In total 167,366 cases of BSE were diagnosed in Great Britain up to June 30, 1997. The cumulative incidence of BSE between July 1986 and June 1997 was 1.10 (95 per cent confidence interval [CI] 1.09 to 1.10) cases per 100 adult cattle at risk. Cattle from the South east, South west and Eastern regions of England had 4.26 to 5.96 (95 per cent CI 4.15 to 6.14) times as great a monthly hazard of being confirmed with BSE as cattle from Scotland. Compared with cattle born before June 1985, those born between July 1987 and June 1988 had 22.5 (95 per cent CI 22.1 to 22.8) times the monthly hazard of being confirmed with BSE, whereas those born in the 12 months after July 1988 had only 7.39 (95 per cent CI 7.24 to 7.54) times the monthly hazard of being confirmed with BSE. This reduction in hazard was directly attributable to the ban on the use of ruminant protein as a feed instituted in July 1988. Successive cohorts from 1989 to 1991 experienced further reductions in the hazard of experiencing BSE. The additional decrease in hazard observed for the 1990 cohort may be attributed to the effect of the Specified Bovine Offal ban instituted in September 1990.  相似文献