黄土丘陵区苜蓿地的土壤呼吸

土地利用的变化会影响到生态系统碳循环过程。中国退耕还林还草工程实施后，大量农田转变为林地和草地。为了摸清退耕后土壤碳排放的变化，在宁夏黄土丘陵区，对退耕苜蓿(Medicago sativa)地、农田和天然草地的土壤呼吸进行了测定。结果表明，土壤温度和土壤呼吸相关性较强，土壤水分和土壤呼吸没有显著相关性；苜蓿地、农田、天然草地的年均土壤呼吸值分别为1.60、1.03和0.85 μmol·m-2·s-1，苜蓿地土壤呼吸比农田高出55.3%，比天然草地高出88.2%;年CO2排放量分别为1 461.96、940.66和777.36 g·m-2·a-1。农田转化为苜蓿地9年后，土壤CO2排放量增加、有机碳含量下降。在黄土丘陵区退耕还草初级阶段，生态恢复措施对固碳增汇的贡献有限。

A study on the soil respiration of alfalfa field in the loess hilly region

Carbon cycle process in ecosystem can be influenced by land use change. After implementing the project of farmlands converted to woodland and grassland in China, a large volume of farmland have been changed into woodland and grassland. In order to study the change of carbon emissions after the abandoned project, soil respirations of alfalfa field (converted from farmland) grassland, and farmland were measured in the loess hilly region of south Ningxia. The results indicated that soil temperature was strongly correlated with soil respiration, and the influence of soil moisture on soil respiration was limited. Average values of soil respiration on the alfalfa field, farmland and grassland were 1.60, 1.03 and 0.85 μmol·m-2·s-1, respectively. The soil respiration of alfalfa field, compared with farmland and grassland, were 55.3% and 88.2% higher. Annual CO2 emissions of alfalfa field, farmland and the grassland were 1461.96, 940.66 and 777.36 g·m-2·a-1,respectively. We concluded that after 9 years of farmland converted into alfalfa field, soil organic carbon decreased and soil respiration increased. The contributions of increasing carbon sink in the stage of farmland converted to grassland were not good as expected.