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241.
Anne Daebeler Paul LE Bodelier Zheng Yan Mariet M Hefting Zhongjun Jia Hendrikus J Laanbroek 《The ISME journal》2014,8(12):2397-2410
Ammonium/ammonia is the sole energy substrate of ammonia oxidizers, and is also an essential nitrogen source for other microorganisms. Ammonia oxidizers therefore must compete with other soil microorganisms such as methane-oxidizing bacteria (MOB) in terrestrial ecosystems when ammonium concentrations are limiting. Here we report on the interactions between nitrifying communities dominated by ammonia-oxidizing archaea (AOA) and Nitrospira-like nitrite-oxidizing bacteria (NOB), and communities of MOB in controlled microcosm experiments with two levels of ammonium and methane availability. We observed strong stimulatory effects of elevated ammonium concentration on the processes of nitrification and methane oxidation as well as on the abundances of autotrophically growing nitrifiers. However, the key players in nitrification and methane oxidation, identified by stable-isotope labeling using 13CO2 and 13CH4, were the same under both ammonium levels, namely type 1.1a AOA, sublineage I and II Nitrospira-like NOB and Methylomicrobium-/Methylosarcina-like MOB, respectively. Ammonia-oxidizing bacteria were nearly absent, and ammonia oxidation could almost exclusively be attributed to AOA. Interestingly, although AOA functional gene abundance increased 10-fold during incubation, there was very limited evidence of autotrophic growth, suggesting a partly mixotrophic lifestyle. Furthermore, autotrophic growth of AOA and NOB was inhibited by active MOB at both ammonium levels. Our results suggest the existence of a previously overlooked competition for nitrogen between nitrifiers and methane oxidizers in soil, thus linking two of the most important biogeochemical cycles in nature. 相似文献
242.
Diving behaviour and foraging location of female southern elephant seals from Patagonia 总被引:1,自引:0,他引:1
C. CAMPAGNA B. J. LE BOEUF S. B. BLACKWELL D. E. CROCKER and F. QUINTANA 《Journal of Zoology》1995,236(1):55-71
Our aim was to describe the free-ranging diving pattern and to determine the location of foraging of pregnant female southern elephant seals, Mirounga leonina , from Peninsula Valdes, Argentina. This colony is unusual in two respects: it is removed from deep water by a broad shallow shelf (345–630 km wide), and colony numbers have been increasing in recent years in contrast to numbers from other southern hemisphere colonies that are stable or in decline. Microprocessor controlled, geolocation-time-depth recorders were deployed on four females, recording a total of 15,836 dives (270 dive days) during the period February to April, 1992. Departing seals crossed the continental shelf quickly (54–5–62–1 h) and did not show signs of foraging until reaching deep water, due east of the colony in the South Atlantic Ocean. Diving was virtually continuous (93% of the time underwater) with overall mean (±S.D.) rates of 2.5±0.2 dives/h, mean dive durations of 22.8 ± 7.1 min (maximum dive duration = 79 min) with 1.6±0.6min surface intervals between dives, and dive depths of 431±193m (maximum dive depth = 1,072 m). The diving pattern of females from Patagonia is similar to that of seals from colonies where numbers are decreasing (Macquarie stock) or are stable (South Georgia Island). Our subjects did not, however, feed in or south of the Antarctic Polar Front, or in cold waters along the Antarctic coast, where seals from declining or stable colonies forage. 相似文献
243.
PATRICK BERREBI GHISLAINE CATTANEO-BERREBI NATHALIE LE BRUN 《Biological journal of the Linnean Society. Linnean Society of London》1993,48(4):319-333
Natural hybridization of Barbus barbus and B. meridionalis has been demonstrated in southern France. A genetical study (isozyme electrophoresis) of these species and their hybrids revealed the characteristics of hybridization. Ten enzyme markers and five morphological parameters were used to distinguish between the two parent species. Enzymatic divergence between the parent species included fixed allelic differences at certain loci and reduction in enzymatic activity, including the silencing of certain genes. A morphological study revealed a good correlation between the isozyme markers and morphological characters. Backcrosses were observed and this raises the question of the integrity of the parent species. 相似文献
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G. W. LE MOAL P. LERAY A.-C. ROUDOT D. THOUVENOT V. VASSEUR 《Journal of Rapid Methods and Automation in Microbiology》1998,6(2):143-156
This paper describes an image analysis method to detect and locate Salmonella colonies grown on Petri dishes, on two different media. The colonies are described using their common feature characteristics: black center surrounded by a clear halation. Morphological image analysis functions are preferred to gray levels because of the color inhomogeneity of the background even under optimal lighting. The results obtained show the good ability of this method for detecting and locating but further work is needed to validate it on a greater number of Petri dishes. 相似文献
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There is scope for land‐use changes to increase or decrease CO2 concentrations in the atmosphere over the next century. Here we make simple but robust calculations of the maximum impact of such changes. Historical land‐use changes (mostly deforestation) and fossil fuel emissions have caused an increase in atmospheric concentration of CO2 of 90 ppm between the pre‐industrial era and year 2000. The projected range of CO2 concentrations in 2100, under a range of emissions scenarios developed for the IPCC, is 170–600 ppm above 2000 levels. This range is mostly due to different assumptions regarding fossil fuel emissions. If all of the carbon so far released by land‐use changes could be restored to the terrestrial biosphere, atmospheric CO2 concentration at the end of the century would be about 40–70 ppm less than it would be if no such intervention had occurred. Conversely, complete global deforestation over the same time frame would increase atmospheric concentrations by about 130–290 ppm. These are extreme assumptions; the maximum feasible reforestation and afforestation activities over the next 50 years would result in a reduction in CO2 concentration of about 15–30 ppm by the end of the century. Thus the time course of fossil fuel emissions will be the major factor in determining atmospheric CO2 concentrations for the foreseeable future. 相似文献
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