E. I. Naumova

Assimilation of biological nitrogen by European beaver

Nitrogenase activity, the abundance of diazotrophic bacteria, the structure and functional characteristics of the complex of microorganisms, and the content of nitrogen and carbon were determined in the contents of the gastrointestinal tract of the European beaver. A high nitrogen-fixing activity in the large intestine correlated with an increase in nitrogen content in the chyme upon its transfer over the gastrointestinal tract. It is assumed that microbial nitrogen fixation plays a major role in nitrogen nutrition of the European beaver.

Some specific features of nitrogen fixation in the digestive tract of the European beaver (Castor fiber).

452 The European beaver ( Castor fiber L. (1758)) is an important component of aquatic and bog ecosystems; in the European part of Russia, its population density reaches nine animals per kilometer of the coastline [1]. Because of beaver activity (the so-called beaver dams), specific landscapes appear that differ from the surrounding ones in some parameters, in particular, the nitrogen content. As determined by Canadian specialists, nitrogen concentration in the water of a beaver dam and in bottom deposits exceeds that in water bodies unaffected by beavers by factors of 30 and 1000, respectively [2]. The accumulated nitrogen is retained in deposits for as long as 72 years and has long-term influence on these ecosystems.

Effect of Deficiency of Dietary Nitrogen on Cellulose Digestibility and Nitrogen-Fixing Flora Activity in Sibling Vole Microtus rossiaemeridionalis

The effect of feed composition on nitrogen-fixing activity of the symbionts living in the digestive tract of sibling vole Microtus rossiaemeridionalis was experimentally studied. In the control, the rodents were allowed to select any of three feeds: protein-rich, protein-free with low cellulose content, and protein-free with high cellulose content. The voles consumed the food in a proportion corresponding to 16% of protein and about 6% of cellulose. Exclusion of the protein-rich food considerably increased cellulose consumption (up to 12%) and digestibility (from 35 to 64%). The changes in the consumed feed composition were reflected in localization of nitrogenase activity in the digestive tract: the control level of nitrogen-fixing activity in the cecum was three times that in the proventriculus, while an inverse proportion was observed in the experimental groups. In all cases, the colon was the major locus of nitrogen fixation.

Specific Features of Nitrogen Transformation in the Soddy-Podsolic Soil in the Colonies of the Common Vole Microtus arvalis

The influence of common vole Microtus arvalison processes of nitrogen fixation and denitrification in the soddy-podsolic soil was studied. In the common vole colonies, the level of nitrogen fixation was reliably lower and that of denitrification higher, than in the control soil outside these colonies. Nitrogen-containing excretory products of voles accumulating in the soil are among the main factors that determine the activity of these processes.

Diazotrophic and cellulolytic component of the internal food chains in the voles Microtus rossiaemeridionalis and Clethrionomys glareolus depending on the feeding specialization.

139 Vegetative parts of plants being food for many rodents are characterized by two factors limiting their consumption, namely, low protein content and high content of hard to digest structural carbohydrates, primarily cellulose. According to the theory of diges tive strategy [1, 2], small mammals, including rodents, cannot use cellulose as a source of energy. However, several publications say that increasing of the cellulose proportion in feed allowance raises its digestion sub stantially [3].

Functional features of microbial communities in the digestive tract of field voles (Microtus rossiaemeridionalis and Clethrionomys glareolus)

The nitrogen-fixating and cellobiohydrolase activity, the nitrogen (N) and carbon (C) contents, and the number of microorganisms in the prestomach, cecum, and colon of two vole species were studied: the southern vole (Microtus rossiaemeridionalis) and the bank vole (Clethrionomys glareolus), which is characterized by a mixed type of diet. The nitrogen-fixating activity in the cecum was found to be the highest in the voles compared with the mammals studied earlier. The seasonal dynamics of both nitrogenase and cellobiohydrolase activities was registered in the southern vole. The structure of the microbial complex in the southern vole is more varied and includes microorganisms associated with plant substrates.

Isolating structures of gerbils’ digestive tract (Gerbillidae, Rhombomys, Meriones) and their functional significance

The morphology of the digestive tract of three species of gerbils characterized by different food specialization—Rhombomys opimus, Meriones tamariscinus and M. meridianus—is considered. The correlation between areas of glandular and cornified epithelium is variable and depends greatly on the type of stomach filling and distribution of food mass in it. The bordering fold and ileocecal junction is not only able to isolate the forestomach and caecum significantly but also may be a mechanism of regulation of food movement through the digestive tract. The close location of ileum’s opening to the caecum and its outlet to the colon, as well as isolation of caecum’s cavity by a circular fold, could provide direct food transit from the ileum to the colon.

Interrelation between size of body and of digestive tract organs in some myomorpha: Isometry or allometry?

Using nonparametric tests, we analyzed the weights of the digestive tract organs of 198 rodent individuals belonging to 11 species of Arvicolinae (family Cricetidae) and Murinae (family Muridae), using both fresh and fixed material, the weight characteristics of which were identical. It has been shown that no unique dependence exists between the body weight and the entire digestive tract one in Arvicolinae rodents weighing 8–73 g. It was also shown that interspecific differences in the relative mass of such a dynamic system of organs as the digestive system cannot always be regarded as a function of the body size alone.

Concentration and size distribution of plant fiber in the digestive tract of muroid rodents

The weight parameters that characterize the size and the degree of fullness of fermentation chambers (forestomach and cecum), namely, the weight of the walls and the content of these organs, and the concentration and size distribution of fibers in the chyme have been investigated in five muroid rodent species (Arvicola terrestris, Microtus oeconomus, Microtus arvalis sp., Clethrionomys glareolus, and Sylvaemus flavicollis). No distinct regularities were observed in the above-mentioned parameters of the forestomach. These parameters of the cecum were generally found to be in good agreement with the conventional concept of dietary specialization of the rodent species under investigation, but the results have provided a more precise assessment of the role of dietary fiber in the diet of free-living rodents under specific environmental conditions.

Role of microbiocenosis of the gastrointestinal tract in the nutrition of grouse

In order to assess the role of the microbiocenosis of the digestive tract of herbivorous birds in transforming poor forage, the activity of cellulolytic enzymes in all departments of the gastrointestinal tract of the black grouse (Lyrurus tetrix) and Western capercaillie (Tetrao urogallus) was studied. The functional diversity of microbial communities of different departments was also investigated. In both species of birds, nitrogenase and cellobiohydrolase activities were discovered in the digestive tract, with the maximum observed in the cecum.