Soil CO_2 flux to the atmosphere is a major factor affecting the global carbon cycle.The CO_2 flux between soil layers is driven by soil temperature,moisture,and substrate supply.Soil CO_2 flux and its major driving factors vary temporally and spatially within soil profiles.However,many studies have focused only on the surface soil,which is insufficient to correctly clarify the actual soil CO_2 release processes,because soil CO_2 flux is the addition of CO_2 production in each soil layer under different biological,chemical,and physical conditions.The vertical distribution of soil CO_2 flux should be considered to better understand the production processes in soil CO_2.Moreover,in the next few decades,an increasing frequency and duration of droughts is expected in subtropical regions in China as a result of global climate change.However,our understanding of the effect of drought on the vertical partitioning of soil CO_2 flux is not well known.In the present study,a throughfall exclusion experiment was established to explore the soil CO_2 flux distribution in the vertical profile in response to simulated drought at two different elevations,including a coniferous forest (CF) at 1450 m.a.s.l and an evergreen broadleaved forest (EBF) at 650 m a.s.l,in a subtropical region in southeastern China from June 2014 to December 2015.We used a CO_2 solid concentration detector to determine the CO_2 concentration at different soil depths,and measured soil CO_2 efflux from surface soils using an Li-8100 soil CO_2 automated measurement system.The soil CO_2 flux at 10,30,and 50 cm soil depths was estimated using the gradient method.The results showed that soil CO_2 concentrations from the CF and EBF plots gradually increased with soil depth.Soil CO_2 production in the 10 cm soil depths in CF and EBF for the control treatment (CK) was 53.5% and 55.7% of the total soil CO_2 production,respectively,indicating that soil CO_2 production primarily appeared in shallow soil owing to the high soil organic carbon and fine root biomass.Drought treatment significantly reduced soil CO_2 flux in each soil layer from CF and EBF.The temperature sensitivity of soil CO_2 flux decreased with increasing soil depth.Drought treatment in CF significantly decreased Q_(10) in the shallow soil (P = 0.02),but there were no significant differences in the deeper soil layers (30 cm:P= 0.30;50 cm:P = 0.23);and in EBF,drought treatment significantly decreased Q_(10) in the deeper soil (30 cm:P = 0.02;50 cm:P = 0.01),but was not significantly different in the shallow soil (P = 0.32).The asymmetric response of Q_(10) in the shallow and deep soil with simulated drought at different elevations implied that the response mechanisms of the shallow and deep soil to drought were different.