Exploitable results Plants/micro-organisms/artificial soil simplified ecosystem This project is based on the study of the interaction plants / micro-organisms. Experiments will consist of an ultra-simplified model of ecosystem plant-artificial soil. The first goal is to compare the growth of plants with and without micro-organisms inoculation, and with and without atmospheric CO2 enrichment. The second objective is to contribute to the understanding of the global changes in natural ecosystems and to overcome the problem of acclimatisation of plantlets after sterile in vitro culture. Special attention will be paid to the evolution of populations of micro-organisms in response to CO2 enrichment, in parallel to the effect on plant growth and development. Identification and numeration of microbial populations will be performed, specifically associated with the roots of the studied plants and particularly stimulated by CO2 enrichment, whose presence, on its own, would be responsible for the observed effects. Special attention will also be devoted to micro-organisms not known in classical symbiotic associations with plants and on microbes directly associated to the roots (rhizoplan). The expected results from the study of the response to the atmospheric CO2 rise will be: to acquire the knowhow of the plant-microbes association in simplified and controlled conditions; to repeat (Canadian) results showing a positive interaction between plant and microbes (in the absence of classical symbioses); to contribute to studies on global climate changes by comparing the response of plants alone or in association with microbes acting as a sink of assimilates and modifying the resulting effect of CO2 enrichment; and to make progress in applied methods using in vitro techniques and a non-axenic culture medium. Results The project is based on the study of interaction «plants / micro-organisms». Experiments have been consisted in an ultra-simplified model of ecosystem «plants- micro-organisms - artificial soil». The experimental work and theoretical investigations were conducted in the following directions: - the first step was to select micro-organisms able to act in co-operation with plant in the view to stimulate their growth. Two strains of Pseudomonas fluorescens and Pseudomonas sp. isolated from plant rhizosphere have been selected, in particular Pseudomonas putida (102-105 bacterial cells per ml) stimulated the growth of roots for 40-60% of their length. - the second step was to compare the interaction between wheat and rhizospheric micro-organism on nitrogen-limited and unlimited artificial soils and on phosphorous-limited and on complete artificial soils. Experiments have shown that on complete mineral medium in comparison with nitrogen limitation, inoculation of plants with bacteria enhanced plant photosynthesis activity by more than 30%, the transpiration rate by more than 50%. The organic nitrogen in the biomass was higher. However, under nitrogen deficiency, the growth characteristics of plants with and without micro-organisms did not reveal significant changes. In the case of the phosphorous parameter, the results have shown no statistically significant differences in the dry weights of plant biomass with and without phosphorous limitation. - the third step was to examine the growth of wheat seedlings with and without micro-organisms inoculation under normal or doubled concentration of atmospheric CO2. With unlimited mineral nutrition and CO2-enrichment the «plants- micro-organisms - artificial soil» system is capable of binding (involving into turnover) 40% more carbon than the «plants-artificial soil» system without microorganisms. The carbon turnover in the chamber with the CO2 enrichment plus Ps. putida inoculation involved substantially more carbon than the «plants-artificial soil» system. The biomass of produced plants represented only 64% of the carbon involved in the system with 36% of carbon in the system used through root exudates for the growth of micro-organism biomass and for their metabolism and respiration. Towards the end of the experiment the living microbial biomass was only 2% of carbon (out of 36%). Half of the carbon that passed through the microbial component has been transformed into CO2 (17%), while the other half (17%) remained in the soil as dead biomass and lysed cells. Two mathematical models on the interaction if rhizospheric micro-organisms on complete mineral medium and under nitrogen limitation and on CO2-enrichment had been constructed from the experimental data. Analysis of data showed that even though the «plants- micro-organisms - artificial soil» system increased the CO2 assimilation rate, the organic carbon destruction rate also increased, so that the balance of carbon in the system was not altered. In our opinion, elevation of carbon dioxide concentration (in the global change prospect) is not obligatory to be supposed to increase its binding in ecosystems and large interactions with other parameters, such as mineral nutrition, should be integrated. Of course, that would need more detailed investigations. Five papers were accepted and three others submitted for publication. Wyszukiwanie danych OpenAIRE... Podczas wyszukiwania danych OpenAIRE wystąpił błąd Brak wyników
