Effect of Soil Moisture and Temperature on the Soil Inorganic Carbon Release of Brown Limestone Soil in the Karst Region of Southwestern China

Abstract

In order to understand the influence of environmental factors on the carbonate conversion of the Karst soil, typical brown limestone and red soil samples were collected from the Karst ecosystem, and a 100-day incubation experiment was conducted. The characteristics of inorganic carbon release from the soil under three temperature gradients (15, 25, and 35℃) and water contents (30%, 65%, and 100% WHC) were studied by adding 14C-CaCO3 for 100 d. The results showed that under the different soil moisture and temperature conditions, the maximum rate and the cumulative amount of inorganic carbon release from the soil over 100 days varied between 0.7-16.8 mg·(kg·d)-1and 5.9-29.4 mg·kg-1, respectively, in the brown limestone soil, and varied between 39.7-103.3 mg·(kg·d)-1 and 83.3-135.1 mg·kg-1, respectively in the red soil. Under drought conditions (30% WHC), the cumulative amount of inorganic carbon release was the highest for the two soils and increased with increasing temperature. At 65% WHC and 100% WHC, increasing temperature can still promote inorganic carbon release from the soil. The temperature sensitivity of the soil inorganic carbon release in the brown limestone soil is greater than that of the red soil, which is significantly affected by soil moisture. The soil pH and MBC content were remarkably increased after adding CaCO3, and the difference between the two soils was significant. The variance partition showed that temperature and soil moisture can explain 7.6% and 2.0% of the soil inorganic carbon release variability, respectively. In conclusion, warming and drought aggravate inorganic carbon release from brown limestone soil in the southwestern Karst region. Therefore, in the context of global warming and more frequent extreme precipitation events, the effects of soil moisture and temperature on inorganic carbon conversion in soil should be fully considered when studying the soil carbon cycle and its dynamic changes in southwestern Karst. This research can provide a scientific basis for further understanding the influence of climate change on the global carbon cycle.