中文摘要：

对比研究中国半干旱-湿润气候区的黄土有机碳同位素（δ13CTOC）变化的控制因素及其所揭示的植被演替过程,能够为认识这些地区植被变化规律提供新的依据.迄今,秦岭以南亚热带地区土壤δ13CTOC与植被和气候之间的关系及其与黄土高原地区的联系还不清楚.本研究选取末次间冰期以来黄土高原的镇北台、西峰、洛川,以及秦岭地区的洛宁和长江下游的镇江等5个代表性黄土剖面,对其δ13CTOC进行对比分析.结果表明,湿润区黄土δ13CTOC在间冰期偏正,在冰期偏负,可以反映季风强度的变化.末次间冰期以来湿润气候条件下黄土沉积区的植被是以C4草本为主的C4/C3混合的草地.温度满足一定条件后,季风降水变化可能是控制半湿润-湿润区黄土沉积上覆C3/C4植物丰度变化的主要因素.

英文摘要：

Comparative studies of environmental factors and vegetation changes deduced from the organic matter stable carbon isotopic composition （δ13CToc） of the loess deposit in semiarid to humid regions would provide clues to understand the vegetation dynamics, in particular under the future climatic changes. However, the relationships between soil organic carbon isotopic composition and vegetation or climate in the subtropical climate areas south of the Qinling Mountains remain unclear. In this study, we selected five loess deposit sections across semiarid to humid climates since the beginning of the last interglacial period at Zhenbeitai, Xifeng, Luochuan which have been reported by other researchers and Luoning （34°25＇ 56.6″N, 111039＇ 23.0″E）, Zhenjiang （32°12＇N, 119°39＇E） in this study to investigate the paleoclimatic and vegetation implication of the δ13CToc. Luoning section located in the temperate sub-humid zones and is 3.8m in depth. The bottom of the Luoning section is about 60ka. Zhenjiang section located in the subtropical humid zones and is about 8m in depth. The bottom of Zhenjiang section is about 130ka. Loess samples were taken at 10cm interval in Luoning section and 20cm interval in Zhenjiang section. The results showed that δ13CToc in Luoning section ranges from -21.8‰ to -19.0‰ and -20.2‰ on average. The δ13CToc have a good correlation with the magnetic susceptibility, and the high values of δ13CToc （-20.2‰- -19.0‰） corresponds to paleosols layers, low values （-21.8‰--20.2‰） corresponds to loess layers. Values of δ13CToc in Zhenjiang section ranges from -21.2‰ to -15.6‰ and -18.0‰ on average. The δ13CToc also have a good correlation with the magnetic susceptibility and high values of δ13CToc （-18.0‰-- 15.6‰） corresponds to paleosols layers, low values （-21.2‰--18.0‰） corresponds to loess layers. Since last interglaciation （Zhenbeitai and Luoning from the last glaciation） the proportions of C4 plant is 12% in Zhenbeitai, 1