土地利用变化对中国土壤碳储量变化的间接影响

Indirect Impacts of Land Use Change on Soil Organic Carbon Change in China

中国土壤有机碳储量及其在全球变暖背景下的变化趋势是影响全球碳循环的一个重要因素。土地利用变化对土壤有机碳储量既有直接影响,也有间接影响。一方面,土地利用变化直接改变了生态系统的类型,从而改变了生态系统的净初级生产力(NPP)及相应的土壤有机碳的输入。另一方面,土地利用变化潜在地改变了土壤的理化属性,从而改变了土壤呼吸对温度变化的敏感性系数(常用Q10表示)。在全球变暖背景下,Q10值的改变显著影响着土壤有机碳释放的强度。利用生态系统碳循环过程模型(CASA模型)反演了不同土地利用类型下的Q10值,并评价了土地利用类型的改变对土壤有机碳储量变化的间接影响。研究结果表明,林地与草地转换成耕地后将增大土壤呼吸的Q10值,此外,人类通过灌溉、氮肥的施用也能增大土壤呼吸的Q10值,从而使得全球变暖背景下土壤呼吸的碳通量有所增强。

Soil organic carbon （SOC） storage and its change trend in China is important to the global carbon cycles under the background of global warming. Land use change has both direct and indirect influences on SOC storage. On the one hand, the land use change directly modifies the original ecosystem type and then makes the net primary productivity and soil carbon input change, which directly impacts SOC storage. On the other hand, land use change modifies some physical or chemical properties of soil and thus potentially impacts the value of temperature sensitivity of soil heterogeneous respiration （ Q10 ）. Under the situation of global warming, the changed Q10 will modify the feedback intensity of soil respiration and then indirectly impacts the soil organic carbon storage. In this study, a regional process-based carbon cycle model （ CASA model） was used to estimate the Q10 values for the different land use types. Basing on the differences of Q10 among land use types, the indirect impacts of land use change on soil organic carbon storage was assessed. The results showed that the land use changes from grassland or forest to cropland will increase the value of Q10. Furthermore, the human activities, such as utilizing of irrigation and nitrogenous fertilizer will also increase the values of Q10. So, the land use change and human activities will potentially increase soil carbon releasing under the situation of global warming and then will indirectly impact soil organic carbon storage.