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391.
392.
Soil enzyme activities in the rhizosphere of field-grown sugar beet inoculated with the biocontrol agent Pseudomonas fluorescens F113 总被引:3,自引:0,他引:3
D. C. Naseby Y. Moënne-Loccoz J. Powell F. O‘Gara J. M. Lynch 《Biology and Fertility of Soils》1998,27(1):39-43
Pseudomonas fluorescens F113, which produces the antimicrobial compound 2,4-diacetylphloroglucinol, is a prospective biocontrol agent. Soil enzyme
activities were used to investigate the ecological impact of strain F113 in the rhizosphere of field-grown sugar beet. There
were distinct trends in rhizosphere enzyme activities in relation to soil chemistry [determined by electro-ultrafiltration
(EUF)]. The activities of enzymes from the P cycle (acid phosphatase, alkaline phosphatase and phosphodiesterase) and of arylsulphatase
were negatively correlated with the amount of readily available P, whereas urease activity was positively correlated with
the latter. Significant correlations between nutrient levels determined by EUF and enzyme activities in the rhizosphere were
obtained, highlighting the usefulness of enzyme assays to document variations in soil nutrient cycling. Contrary to previous
microcosm studies, which did not investigate plants grown to maturity, the biocontrol inoculant had no effect on enzyme activities
or on soil chemistry in the rhizosphere. The results showed the importance of using homogenous soil microcosm systems, also
employed in previous work, for risk assessment studies, whereby the effects of inherent soil variability were minimised, and
effects of the pseudomonad on soil enzymology could be detected.
Received: 3 February 1997 相似文献
393.
The phase velocities of Rayleigh waves increase more rapidly with distance from the East Pacific Rise (EPR) axis than is predicted by models of conductive cooling of the lithosphere. Low velocities near the axis are probably caused by partial melt at depths of 20 to 70 kilometers in a zone several hundred kilometers wide. The lowest velocities are offset to the west of the EPR. Wave propagation is anisotropic; the fast direction is approximately perpendicular to the ridge, parallel to the spreading direction. Anisotropy increases from a minimum near the axis to 3 percent or more on the flanks. 相似文献
394.
Predatory dinosaur remains from madagascar: implications for the cretaceous biogeography of gondwana 总被引:1,自引:0,他引:1
SD Sampson LM Witmer CA Forster DW Krause PM O'Connor P Dodson F Ravoavy 《Science (New York, N.Y.)》1998,280(5366):1048-1051
Recent discoveries of fossil vertebrates from the Late Cretaceous of Madagascar include several specimens of a large theropod dinosaur. One specimen includes a nearly complete and exquisitely preserved skull with thickened pneumatic nasals, a median frontal horn, and a dorsal projection on the parietals. The new materials are assigned to the enigmatic theropod group Abelisauridae on the basis of a number of unique features. Fossil remains attributable to abelisaurids are restricted to three Gondwanan landmasses: South America, Madagascar, and the Indian subcontinent. This distribution is consistent with a revised paleogeographic reconstruction that posits prolonged links between these landmasses (via Antarctica), perhaps until late in the Late Cretaceous. 相似文献
395.
L. M. Kawchuk D. R. Lynch G. C. Kozub G. A. Nelson F. Kulcsar D. K. Fujimoto 《American Journal of Potato Research》1998,75(6):235-243
The expression of foliar and tuber bacterial ring rot (BRR) symptoms in 108 cultivated potato genotypes inoculated withClavibacter michiganensis subsp.sepedonicum was examined in field experiments during 1986 to 1996. Considerable variation in the incidence of foliar BRR symptoms was observed in all plant cultivars, ranging from no detectable symptoms to complete necrosis of the leaves. Similar variability was observed in the incidence of tuber BRR symptoms, and severity of tuber symptoms ranged from no detected symptoms to complete breakdown of the vascular ring that extended throughout the tuber. A decline in the incidence and severity of tuber, but not foliar symptoms, was observed in the later years of the study (P<0.05). Foliar and tuber BRR symptoms generally were positively correlated (P<0.01) prior to 1993 but not in subsequent years (P>0.05) when tuber symptoms declined. Strong correlations were observed between the incidence and severity of foliar BRR symptoms (r=0.41, P<0.01) and between the incidence and severity of tuber BRR symptoms (r=0.96, P<0.001). During the 11 year period, no BRR symptoms were observed in 2,620 uninoculated control plants. 相似文献
396.
- 1. 309 Great Barrier Reef Marine Park recreational fishers were surveyed to examine recreational catch and harvest of elasmobranchs and to explore recreational fishers' handling behaviour and attitudes.
- 2. Elasmobranchs represented 6% of fishers' total catch of all fish (including released individuals), and 0.8% of fishers' total harvest (i.e. retained individuals) across all survey days. The majority of elasmobranchs caught by fishers were released, primarily because they were perceived as being inedible.
- 3. Recreational fishers' self‐reported handling and release behaviour for elasmobranchs is largely consistent with ‘best practice’ guidelines except that fishers had low use of circle hooks and barbless hooks, and a significant proportion (33%) reported using stainless steel hooks.
- 4. Most fishers had positive attitudes towards elasmobranchs, placing high importance on releasing sharks and rays in good condition (86%), high value on their existence (84%), and low value on catching them (63%).
- 5. Results indicate that post‐release mortality is probably the largest source of recreational fishing mortality of elasmobranchs in the Great Barrier Reef. Future research should be targeted at obtaining better estimates of species‐specific post‐release mortality levels, understanding how post‐release survival can be increased by changing fishing techniques or fisher behaviour, and developing more effective methods of engaging fishers in elasmobranch conservation. Copyright © 2009 John Wiley & Sons, Ltd.