Experimental and mathematical modeling of the consumer's influence on productivity of algae in a model aquatic ecosystem.

A "producer-consumer" (Chlorella vulgaris-Paramecium caudatum) closed aquatic system has been investigated experimentally and theoretically. It has been found that there is a direct relationship between the growth of the paramecia population and their release of ammonia nitrogen, which is the best form of nitrogen for Chlorella growth. The theoretical study of a model of a "producer-consumer" aquatic biotic cycle with spatially separated compartments has confirmed the contribution of paramecia to nitrogen cycling. It has been shown that an increase in the concentration of nitrogen released as metabolites of paramecia is accompanied by an increase in the productivity of microalgae.

Population dynamics of an algal-bacterial cenosis in closed ecological system.

The paper deals with microalgae-bacteria interrelationships in the "autotroph-heterotroph" aquatic biotic cycle. Explanations of why and how algal-bacterial ecosystems are formed still remain controversial. The paper presents results of experimental and theoretical investigations of the functioning of the algal-bacterial cenosis (the microalga Chlorella vulgaris and concomitant microflora). The Chlorella microbial community is dominated by representatives of the genus Pseudomonas. Experiments with non-sterile batch cultures of Chlorella on Tamiya medium showed that the biomass of microorganisms increases simultaneously with the increase in microalgal biomass. The microflora of Chlorella can grow on organic substances released by photosynthesizing Chlorella. Microorganisms can also use dying Chlorella cells, i.e. form a "producer-reducer" biocycle. To get a better insight into the cenosis-forming role of microalgae, a mathematical model of the "autotroph-heterotroph" aquatic biotic cycle has been constructed, taking into account the utilization of Chlorella photosynthates and dead cells by microorganisms and the contribution of the components to the nitrogen cycle. A theoretical study showed that the biomass of concomitant bacteria grown on glucose and detritus is larger than the biomass of bacteria utilizing only microalgal photosynthates, which agrees well with the experimental data.

Kinetic characteristics of the theoretical ecosystems with different extent of openness.

In this paper, the influence of the extent of openness of ecosystem that is defined by the dilution rate, which characterizes the extent of flowage of the pond, on the intensity of the biotic circulation in ecosystems with different regulation types, number of trophic links and extent of closing has been investigated. We considered open systems, we took into account the return of the limiting substances, such as nitrogen and phosphorous, into the cycle by degradation of detritus and products of vital functions of consumers. It was shown by the numerical calculations that the increase of the dilution rate in without recycle ecosystems leads to increase of the net primary production up to the maximum value corresponding to the two-link trophic chain (biogenic substance and producer) and then, to gradually decrease. The residual concentration of biogenic limiting substances monotone increases. Net primary production and residual concentration of biogenic limiting substances in systems with recycle with even number of links behaves similarly to that in without recycle ecosystems. In the systems with recycle with the odd number of links that values lies on the stable level. We showed that in wide range of the dilution rate the recycling of the ecosystem can highly increase the net primary production and reduce residual concentration of biogenic limiting substances. The influence of the dilution rate on numbers of links that may exist in the system was analyzed.