For the in situ measurement of nitrogen fixation in lake sediments, we developed a method which assures the rapid saturation with acetylene of the whole enzyme pool in the sediment and maintains near intact physical, chemical and biological environment a t the water-sediment interface. On the basis of seasonal measurements, the annual nitrogen fixation in the sediment was estimated in four types of shallow water ecosystem: the Keszthely Basin, Lake Balaton: 4.7 g N m-2; Koros backwater reservoir: 6.5 g N m-2; a polycultural fishpond: 0.49 g N m-2; and a liquid manure oxidation fishpond: 0.61 g N m-2. The amount of nitrogen fixed in the sediment of the Keszthely Basin was close to the fixation in the water column, while that fixed in the sediment of Koros backwater reservoir was considerably greater.A multiple regression analysis was made on the basis of synoptic studies on the vertica,l distribution of nitrogen fixation in the sediment, the pH, Eh, and concentrations of organic N, NH,-N, N03-N, and N02-N in the interstitial water. The results indicate that nitrogen fixation is related to the depth, the NH,-N concentration, and the redox potential. The vertical distribution of nitrogen fixation cannot be explained in every case by the densities and distributional patterns of the Azotobacter and Clostridium populations. No correlation was observed between nitrogen fixation and total organic-C in lake sediment. A surprisingly close correlation was found between plankton primary production and the sedimentary nitrogen fixation in these lakes ( r =0.85, y=4.5XO.85). Short-term (4 h) in vitro studies revealed a glucose mediated increase of nitrogen fixation, but there was no NH,-N inhibition detected during this short incubation period.
The present study was performed in order to examine the effect of using marjoram extract as a natural growth promoter on performance and intestinal bacteria of broiler chickens. Marjoram extract was prepared by the maceration method. Then, an in vitro trial was conducted to determine the antibacterial activity of marjoram extract against six bacterial strains. The results of the antibacterial disk diffusion test showed that marjoram extract has a high inhibitory effect against both Gram-positive and Gram-negative bacteria. Later on, an in vivo feeding trial was done using 90 dayold Ross broiler chicks. The chicks were divided into two groups of three replicates each. The first group served as a control without any supplementation while the second group was supplemented with marjoram extract as a growth promoter. The results showed that addition of marjoram extract led to a significant (p<0.05) improvements in final live body weight, total weight gain and total feed intake of broiler chickens. On the other hand, the relative weights of internal organs were not affected by marjoram extract supplementation. The total aerobic intestinal bacteria count of the broilers fed the marjoram extract supplemented diet was significantly lower (p<0.01) than that of the control group. The overall results suggest that marjoram extract could successfully be used as a natural growth promoter alternative to antibiotic in broilers' diets.
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