中文摘要：

末次冰期以来陆地植被中C3／C4植物相对丰度变化及其驱动因素是当前古生态古气候研究中的重要内容．本文利用雷州半岛北部下录和屋山两处泥炭沉积有机碳同位素组成（δ13Corg）重建了该区域末次冰期以来C3／C4植物相对丰度演化历史，并探讨了其可能的驱动因素．结果表明，在MIS-3阶段初期，屋山地区的植被以C3和C4混合植被为主，在此后的MIS-3阶段绝大部分时期，下录和屋山地区的植被主要为C3植被，在个别时段C4植物也曾一度有所扩张；在MIS-2阶段，下录地区c，植物含量显著降低，区域植被以C4植物为主；在全新世初期，下录地区的C3植物含量呈现出增加趋势，气候环境变得有利于C3植物生长．对比研究表明，由于在末次冰期乃至冰期最盛期阶段，雷州半岛地区的气温下降幅度可能仅在5～8℃左右，温度足以满足C3／C4植物的生长需要，从而使得受东亚夏季风强度直接影响的降水增多或减少成为控制本区域C3／C4植物相对丰度变化的主导因素．此外，大气CO2浓度可能对该地区C3／C4植物相对丰度变化也具有一定的影响．

英文摘要：

The relative abundance of C3/C4 plants since the Last Glacial Age and its possible driving mechanisms are the key con- tents in the fields of paleoecology and paleoclimate research. Here we present a new organic carbon isotope （ δ13 Corg ） time series of peat sediments, spanning from 61000 cal a B.P. to 10000 cal a B. P. , derived from the northern Leizhou Peninsula. To better understand the past vegetation responses to the climatic and environmental changes, we estimated the relative abundance of C3 and Ca plants using the δ13 Cotg records and compared them with other climatic records. The estimated results indicate that the vegeta- tions in the study region were mainly composed of mixture of both C3 and Ca plants in the early stage of MIS-3. During the rest of the MIS-3, C3 plants were dominant, although C4 plants expanded to a certain extant during certain periods. During the MIS-2, the relative abundance of C3 plants decreased significantly and C4 plants expanded greatly. At the beginning of the Holocene, the proportion of C3 plants seemed to increase gradually. Variations of the relative abundance of C3 and C4 plants in the northern Le- izhou Peninsula was similar to the pattern of East Asian monsoon intensity reconstructed from the stalagmites records, suggesting that the East Asian monsoon intensity accompanied with the changes in monsoonal precipitations exerted a very strong control on the relative abundance of C3 and C4 plants. It is likely that the temperature threshold, which is normally an important factor in high latitudes, may be less important in influencing the relative abundance of C3 and C4 plants in tropical southern China. The atmospheric CO2 concen- tration may also partly superimpose some influences on the variations of relative abundance of C3 and C4 plants at orbital scale.