The Study On The Change Of CO₂ Release From Soil In Guanzhong And Luochuan Area

This study focuses on such areas as the southern part of Xi' an and near Lantian county. Xi'an and Lantian are in the middle part of Guanzhong plain of Shaanxi province, in the south beyond Wei River and the north beyond Qin Mountain, and on the second terrace of Wei River. The topsoil layer is usually composed of Malan loess. Because its composition is homogeneous and its construction is loose, it's the ideal layer to be studied for CO2 release. In the research areas, natural vegetation is hardly seen, but crops, artificial vegetation and secondary vegetation. This region has warm temperate and continental monsoon climate with 4 distinct seasons.The method used in this study is alkali aqua absorption. The observation, which lasted nearly from November 2002 to December 2003, shows that the amount of COa release from thick soil layer does not have the positive correlation with the change of temperature, which is different from other studies on other areas, that is to say the release amount in the daytime is lower than that at night. The change law of release amount of CO2 from thin soil layer has the positive correlation with temperature. The release amount of the thin soil layer is less than that of the thick soil layer.The research shows that the release amount from soil decrease and then rises and again decreases throughout the day and night from 8:00AM to 8:00AM next day. The release of CO2 in the soil tends to keep pace with the temperature change, however the change of the former is later than that of the latter. Usually, from 11:00 to 14:00, the least is released from the soil, and then the release amount of CO2 increases rapidly and reaches its climax around the time period from 19:00 to 23:00.About 6:00 in the morning, the amount declines apparently. The change law of release amount of CO2 from thin soil layer is different from that of thick soil layer, the release amount is great from 9:00 to 18:00, decrease from 18:00 to 21:00, is small from 21:00 to 6:00 the next day and increases after 6:00.The amount of CO2 release from soil in Guanzhong area changes all the yearround, with the highest amount in the summer, next autumn, and the lowest in the winter. Usually, the amount of CO2 release per day is found to be the highest in July, which is over 8g/m2-d, and the lowest in December, January and February, which is less than 0.5g/m2-d.Temperature is the most important factor affecting the CO2 release. Temperature plays an apparently more important part. By statistic analysis, the amount of CO2 release shows extremely obvious positive correlation with temperature with the globe becoming warm, the amount of CO2 emission will increase.The release of CO2 in the soil is sensitive to the soil layer and vegetation. The release amount of thin soil layer is apparently little than that of thick soil layer because the vegetation of thin soil layer is more than thick soil layer. The release amount of CO2 varied under the different conditions of vegetation. Generallyspeaking, there is a higher release amount of CO2 on the bare ground, but a lower amount on the woodland and grassland. It's found that t the CO2 release from the bare ground changes frequently, while it is more stable if the ground is covered by vegetation.Microorganism primarily produced the CO2 in soil. According to the change of CO2 release, it's deduced that microorganism is more active at night than in the daytime.The experiment shows vegetation plays an important role in slowing down the release of CO2 in soil and protecting the environment. The protection of vegetation and enhancement of ecosystem is one of the effective measures to curb CO2 in the atmosphere. Therefore, the restoration and construction of the forest, and enlargement of Carbon sinks on the continent is an important aspect in the environment construction from now on.