Abstract:

The carbon cycle in karst area is the perfect joint combining geological process with biological process, so it is very important for accurately estimating the carbon sink effect of karstification to systemically study limestone weathering in farmlands. Taking a hydrological year as a period, corrosion experiment of the standard limestone tablets in farmland samples such as yearround flooded paddy field, seasonal rotation paddy field, vegetation plot, dry land, grassland, unutilized land and so on has been observed. Based on the limestone corrosion experiment, on the investigation of soil profiles and biomass of vegetation in the same farmlands, and on the analytical experimentation of soil and the standard limestone tablets, the characteristics of corrosion of limestone in farmland ecosystems in the area and its influence factors have been analyzed. The result shows that the corrosion ratio decreases successively from seasonal rotation paddy field, to vegetation plot, to dry land and to yearround flooded paddy field. There are obvious differences, and complex changes among corrosion ratio at different soil layers of farmlands in Sanquan Town, Nanchuan City. Karstification in farmland ecosystem in the area is more intense than that in nonfarmland ecosystems, and the average annual flux of CO2 absorbed by karstification in farmland ecosystems in the town is 163.1264×105 gC/(km2·a). The annual flux of CO2 absorbed by karstification in farmland ecosystems in the region is larger than that in nonfarmland of other areas at the same latitude. Principal component analysis shows that karstification in farmland in the region is mainly affected by the location of soil layer, the kinds of farmland, the seasonal change of farmland and the matter sources of soil in farmland ecosystem.

Key words:  farmland ecosystem, karstification, carbon sink, Sanquan Town, Nanchuan City