Changes in soil profile temperature, moisture content, and CO2 concentration during the initial stages of natural vegetation restoration of abandoned farmland in karst regions

Due to the implementation of various vegetation restoration measures, vegetation recovery is remarkable in karst areas of Southwest China, which is the main region for global greening. However, the effects of natural vegetation restoration on the soil profile microenvironment, particularly in karst regions, remain largely unknown. From 2018 to 2021, we continuously monitored the soil temperatures, moisture contents, CO₂ concentrations and stable carbon isotopic compositions of the four soil profiles in the naturally restored region of Puding Karst Ecosystem Research Station to reveal their changes resulting from natural vegetation restoration for abandoned farmland in karst regions. The results showed that at the initial stage (herbaceous stage) of natural vegetation restoration, the initial weeds were gradually replaced with a single dominant species, with the C4 plants Imperata and Miscanthus becoming the main contributors to the vegetation biomass of the abandoned farmland. The soil profile temperature and moisture content decreased. The soil moisture content significantly decreased at a depth of 40 cm. The soil profile CO₂ concentration showed both increase or decrease. During the restoration from weeds to the single species Imperata, the soil CO₂ concentration increased, and the δ¹³C values gradually became positive. In comparison, during the restoration from weeds to the single species Miscanthus, the soil profile CO₂ concentration decreased, and the δ¹³C values gradually became positive. Moreover, the increase in soil porosity enhanced the carbon exchange between the soil and the atmosphere. Dominant species slow down positive succession, and artificial interventions are needed to enhance biodiversity and ecosystem stability.