Sites in Ganryuji with mineral springs and Torijigoku with pure carbon dioxide（CO_2）springs were examined for their potential as experimental areas to study the effects of elevated atmospheric CO_2 concentration on soil-plant system. Soils in Ganryuji mineral spring was highly contaminated with mineral spring water. Torijigoku CO_2 spring emits very high concentration of CO_2（>30%）at a vent soil surface. Average CO_2 concentration in the middle part of the grassland was 500-1000ppm in the afternoon. Torijigoku was an ideal site for the assessment of elevated atmospheric CO_2 on plant responses, but the soil structure was estimated to be disturbed by mudslide under heavy rainfall or by snow melting water. It is therefore necessary that we should consider the factors, i.e. microtopography and so on, other than the high atmospheric CO_2 concentration in order to evaluate the elevated atmospheric CO_2 concentration on soil properties.