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Distribution of CO2 in Soil Air Affected by Vegetation in the Shilin National Park

This paper studies the CO2 distribution of soil atmosphere in the Shilin National Park. The measurement sites were chosen according to different topographic features and different vegetations. Seven measurement sites on 3 cross sections were chosen to pass through 3 karstic depressions or on the slopes of depressions. All measurement results show soils with pH values lower than 7.0 (from 5.4 to 6.6). There are 2 cases for the pH values of soil in different topographic features: the pH values of 2 profiles on the ridges or upper slopes of depressions are lower than those in the depressions; and the pH values of 2 soil profiles on the slopes of depressions are higher than those in the depressions. Most samples show relatively low humidity and CO2 contents on the ridges or slopes of depressions compared with soil profiles in the depressions. High CO2 contents occur at depths from −40 to −80 cm and high and dense grassland shows high CO2 contents in the soil atmosphere. Grass roots may grow and are distributed mainly at depths from −20 to −40 cm; while tree roots predominantly as deep as −60 cm even −80 cm. The influences of pine, cypress and eucalyptus on soil CO2 have been studied. Soil CO2 influenced by pine and cypress are generally concentrated in an area surrounding the tree with a diameter of 1 m and the strongly influenced distance is 50 cm. Eucalyptus will strongly affect the CO2 contents in an area with a diameter of 2 m, especially 1 m distant from the tree. The highest concentration of soil CO2 at a depth of −30 and 100 cm from the tree reaches 92000 ppm.