2.1 Study site
Three sites have been chosen for field experiments based on the careful consideration of geological, geomorphic, and climatic conditions in Guizhou Province, central Southwest China (Figure 1). Table 1 shown the main geographic environment information of three experiment sites. Site A (27°15′37″N, 105°5′58″E) lies to the Northwest Guizhou, with a relatively cold and dry climate. The topography surrounding the experiment site is a typical karst valley, mostly composed of carbonate rock. Azonal yellow soil covers a large area of Site A, which varied from a few centimeters to approximately one meter in depth. Apart from a thick soil layer in the valley bottom, there is not much soil on steep slopes. The valley has a mixed coniferous and broad-leaved forest on the upper part of the hillside, and a few patchy shrub or grass cover underneath. Site B (26°33′1″N, 106°19′18″E) is located in a relatively temperate climate region in the central of Guizhou province. A field experiment of Site B was conducted in a giant karst valley. The exposed rock of the valley is relatively pure limestone, which is in contact with a thicker yellow soil above the bedrocks. Compared with Site A, Site B has various vegetation types, mostly consisted of evergreen broad-leaved forest and deciduous broad-leaved forest. The Site C (25°5′9″N, 105°19′48″E) is located in a flat karst basin and mainly outcrop rock is dolomitic limestone. As an experiment site in the southwest of Guizhou, which has a humid and warm subtropical climate. The soil around the experiment site is calcareous soil and zonal yellow soil. Due to its suitable climate and soil conditions, the vegetation of these areas is in good condition; most of them are evergreen broad-leaved forest.
These three filed experiment sites are all the typical karst valley or basin landform, and the prominent outcrops are carbonate rocks. The soil and vegetation around these experiment sites are zonal soil and vegetation in Southwest China. From Site A to Site C, the climatic condition gradually changes from a dry and cold climate to a warm and humid environment. The exogenous situation of karst dissolution in three sites is distinct, and it can be regarded as a typical representative of different karst topography in Southwest China.