In order to reveal the significance of soil CO2 on cave environment

statistical and regression analysis were conducted on the related data of the cave environmental indexes and the overlying soil properties in 2016. The results showed that the cave air CO2 concentration and soil CO2 concentration presented the significant seasonal variation and obvious hysteresis phenomenon. The difference between summer and winter of cave air CO2 concentration corresponded with soil 2# was 793～884 mg/kg. The highest differences of soil water PCO2 and drip water PCO2 between summer and winter were 1.12 and 0.41 respectively. So the drip water PCO2 and soil water PCO2 also showed obviously seasonal variations. The lag phenomenon was shown among soil CO2

cave air CO2

drip water PCO2 and soil water PCO2

e.g.

the coefficients between soil water PCO2 of soil water and drip water were improved from 0.123 without hysteresis to 0.596 with hysteresis. Under the hysteresis

the highest total contribution of soil CO2 concentration to cave air CO2 concentration was 84.6%

higher than that without hysteresis.