海北高寒草甸土壤有机碳同位素组成及C3/C4碳源的变化

通过对高寒嵩草草甸土壤剖面不同深度(0～5cm，5～15cm，15～25cm，25～35cm，35～50cm，50～65cm)有机碳稳定性碳同位素的测定发现，土壤有机碳稳定性同位素(δ^13C)随土壤深度的增加而变大。表层土壤(0～5cm，定义为现代土壤)的δ^13C值最小，基本上接近现代植被的碳同位素特征。在土层5～10cm深度以下(粗略地定为古土壤)，土壤有机碳稳定性同位素骤然上升，与表层土壤的同位素特征明显不同。考虑到影响土壤碳同位素的诸多因素，通过稳定性碳同位素的质量平衡模型计算，得出初步结果：来自C4(或CAM)植物的碳源随土壤深度的增加而增大。进一步推测，该地区植被可能经历由C4植物占优势的群落向C3植物占优势的群溶演化的过程。在这个过程中，大气碳同位素的变化和土壤有机质的形成过程(有机质淋溶过程)等也会引起土壤碳同位素的升高，因此质量平衡模型可能会过多地估算C4组分，而低估C3组分。

Stable Carbon Isotopic Composition in Soil Organic Carbon and C3/C4 Source Variations at the Haibei Alpine Meadow

Stable carbon isotopes of organic matter originated from different soil layers (0～5 cm, 5～15 cm, 15～25 cm, 25～35 cm, 35～50 cm, 50～65 cm) were investigated in the Haibei Alpine Meadow Ecosystem Research Station of the Chinese Academy of Sciences. The preliminary results indicated that δ13C values of soil organic matter increased with increased soil depth. δ13C of soil organic carbon in 0～5 cm layer showed the lowest value, -25.09‰; while 50～65 cm soil layer possessed the lower δ13C value, -13.87‰. Based on mass balance model of stable isotopes, it was proposed that the percentage of C4 carbon source tend to increase with increased soil depth. The preliminary study indicated that alpine meadow might have undergone a successive process from C4-dominated community to C3-dominated one. However, changing δ13C values in atmospheric CO2 overtime and different processes of soil organic carbon formation (or eluviation) might somewhat contribute to increasing δ13C values. In this case, mass balance model would underestimate C3 community and overestimate C4 community.