6 Abstract Temperate forests serve as long term carbon storage and are affected by increasing carbon dioxide (CO2) concentration in the atmosphere. Norway spruce (Picea abies (L.) Karst.) is the most abundant conifer in the forests of the Czech Republic, therefore I studied the response of its photosynthetic aparatus to elevated CO2 concentration. The aim of my thesis was to analyze the impact of CO2 concentration on chloroplast ultrastructure in both shaded and exposed needles, focusing on the volume density of starch in the median cross-sections of mesophyll cell chloroplasts. The next aim of the study was to test whether the chloroplasts of the first subepidermal layer of mesophyll are representative for the whole needle with respect to starch volume density. The study was performed on eleven years-old Norway spruce trees that had been exposed to ambient or elevated concentration of CO2 for six years; the experiment had been carried out at the Bílý Kříž experimental station in the Beskids Mountains in cultivation chambers with automatically adjustable windows. First year needles of trees grown under abient (382-395ppm) or elevated (700 ppm) CO2 concentration were collected in October 2011. The needles were used to prepare ultrathin sections and the images of median chloroplast cross-sections were...