Abstract: A tract of 20 year old Eucalyptus sp. forest in the Yaoshan Mountain of Guilin was selected as research subject for monitoring of diurnal variation of soil respiration and environmental factors in the four seasons, separately, from January to November 2013. (1) The diurnal variation of soil respiration in the forest was quite apparent, displaying a single-peak or double-peak curve. The soil respiration rate varied sharply, rising to the peak at 17:00-19:00, and dropped to the valley at 5:00-9:00, in a day in all the four seasons, which demonstrates that soil respiration was high and active during the day, but low and fluctuating within a narrow range at night. (2) Total soil respiration rate differed significantly between the seasons,（P<0.05）, displaying an order of summer > spring > autumn > winter. In terms of autotrophic respiration contribution rate, the four seasons followed an order of spring > winter > summer > autumn. (3) Soil total respiration rate, soil autotrophic respiration rate and soil heterotrophic respiration rate were significantly and positively related to soil temperature (P<0.05), and the latter could be held responsible for 64.18%, 15.43% and 83.58% of the changes in the three rates, respectively. (4) Soil total respiration rate, soil autotrophic respiration rate and soil heterotrophic respiration rate were also significantly and positively related to soil moisture content (P<0.01). Soil moisture content in a certain range could promote soil respiration.

Key words: soil respiration rate, diurnal variation, temperature sensitivity, Eucalyptus sp., Yaoshan Mountain of Guilin