Khalaim O. Estimation of CO2 fluxes in model steppe ecosystems under altered precipitation

In the thesis the intensity of emission and absorption of CO2 by model steppe ecosystems of the Karadag Nature Reserve under altered precipitation (increasing and decreasing the natural rainfall level by 20%, 40%, and 60%) has been estimated by the chamber method with the use of an infrared gas analyzer. It has been shown that the studied ecosystem and soil CO2 fluxes react nonlinearly to altered precipitation, while gross productivity monotonically increases with an increase in the humidity level within +/- 40% of the natural level. It has been found that the studied model steppe ecosystems serve as a source of CO2 emissions, and the soil respiration is one-third of the total CO2 emissions. It has been found that seasonal fluxes of CO2 depend not only on the amount of precipitation but also on the increase of the time interval between the rains and their intensity. A scientific and methodological basis for further work on forecasting the reaction of carbon cycling of steppe ecosystems to climate change has been developed. For the first time a methodological work was done on correction of the well-known chamber gasometric method of measurement of CO2 fluxes for steppe ecosystems in the South of Ukraine: the optimal time frames for daytime measurements of CO2 fluxes and the optimal duration of data recording were established. Key words: CO2 fluxes, model steppe ecosystems, carbon cycling, altered precipitation, gross ecosystem productivity, net ecosystem exchange, ecosystem respiration, soil respiration.