Abstract: This paper studied the soil physical properties, soil CO2, soil water and spring water chemistry in a mature forest and a shrub in Nongla of Guangxi, China, as well as the relationships between the chemistry of soil water and spring water, aimed to understand the karst effect of the soil water in Nongla epikarst dynamic system. Significant differences were observed in the soil bulk density and non-capillary porosity under forest and shrub, which affected soil water content. The fixed CO2 in soil water had a significant negative correlation with soil CO2, and the free CO2 in soil water was 0 mg·m-3 in the forest and 533×103mg·m-3 in the shrub. In soil water and spring water, there was a negative correlation between pH and Ca2＋, Mg2+, and Cl- concentrations, and a positive correlation between K+, Na＋, and HCO3- concentrations and organic C content. After the eluviation of rain water, the ion concentrations in leached soil water increased greatly, and accordingly, its corrosion ability enhanced greatly. The karst process in forest environment was stable and intensive, while that in shrub environment was active but weak.

Key words: Chinese fir plantation, litter, priming effect, soil organic carbon mineralization, microbial biomass carbon.