Thermal desorption of deuterium(D) from 8-keV D-ion irradiated beryllium(Be) above room temperature was correlated with microstructural changes during irradiation and annealing to understand the underlying mechanism of retention and trapping of D. D bubbles are formed at all examined temperatures between 300K and 873K. Large roundish bubbles above 200nm are especially formed above 573K. They remain even after annealing up to 973K. Strong retention of D by the bubbles occurs for the irradiation up to 673K.