Abstract: Soil respiration is the process of soil releasing CO₂. It is important to explore the dynamics of soil CO₂ and its controls for mechanistic understanding of the terrestrial carbon budget and global climate change. Using infrared sensors (Vaisala GMP252) and an automatic device, we monitored CO₂ concentration and apparent respiration rate (i.e., soil surface CO₂ flux) of a limestone soil profile with high frequency, aiming to capture the diurnal dynamics of soil CO₂ and its relationship with soil temperature, soil moisture and intense rainfall during summar. The results showed that the diurnal dynamics of soil CO₂ concentration generally exhibited singlepeak curves, with a maximum during 12:00-13:00  each day. Moreover, soil CO₂ concentration showed a V-shaped response to intense rainfall. Soil CO₂ had a positive correlation with soil temperature, but had a negative correlation with soil moisture. The equilibrium of HCO₃^-, CO₃^2- and CO₂ in the water filling in soil porespace during rainfall may have impacts on the CO₂ concentration dynamics in limestone soil due to its alkaline property. The apparent soil respiration rate had a similar diurnal variation trend as soil temperature and CO₂ concentration, showing significant correlation with temperature, while the poor correlation with soil CO₂ concentration. Soil temperature and moisture explained 45% of the variation of apparent soil respiration rate. Our results indicated that with the impacts of intense rainfall events, short-term apparent soil respiration of limestone was mainly controlled by CO₂ exchange between soil and atmosphere, which was largely dependent on environmental factors such as rainfall, soil temperature and moisture.

Key words: northern grassland, GIMMS NDVI, phenology, climate