Aliphatic des-A-triterpenes,the degradation products of pentacyclic triterpenes have been tentatively assigned in samples taken from a 963-cm-thick peat sequence from the Hani region of Northeast China using gas chromatography-mass spectrometry(GC-MS)in order to understand and identify these des-A-triterpenes response to climate and ecology.The study indicates that aliphatic des-A-triterpenes are abundant in the Hani peat bog.The high relative abundance of the total des-A-triterpenes mainly occurs at the Holocene periods and is corresponding to the low sedimentation rate.The mechanism of des-A-triterpenes accumulation is not consistent with the previous studies.It is proposed that the biological community is also one influence factor.The obvious stage variations of the total des-A-triterpenes in the whole sequence reveal the different biological(microbes and plants) processes and responses,possibly revealing the four large replacements of biological community and functional composition in the swamp environment over the 16000 cal a BP.The low total des-A-triterpenes values occur at about 10200,8700,7700,6600,4480-3940 and 3040 cal a BP,reflecting the multiple millennial micro-environment oscillations under the macro-environment of the swamp during the Holocene.The ratios of diene and monoene des-A-triterpenes(DT/MT),des-A-lupane and diene and monoene des-A-triterpenes(DL/(DT+MT)),ratios ofindividual compounds exhibit vertical opposite to the total des-A-triterpenes. Namely,these ratios are high during the last deglaciation and late Holocene whereas they are low at other periods,indicating different compounds have different responses to micro-environment and microbial activities.This study discusses the diversity of biological community and biological functional composition response to micro-environment,which not only provides the complement in Northeast China,but also bears important fundamental information for the implication to ecological environment in the future.
We report the results of a comparative study of n-alkane biomarkers and pollens in lacustrine and peat deposits at Dingnan, Jiangxi Province in southern China, and discuss the likely causes for the dis-crepancy in the interpretations of the n-alkane biomarker and pollen records in terms of climate and vegetation change. The results show that past changes in climate and vegetation revealed by the n-alkane record are not always consistent with the pollen assemblage record in the whole section. Biomarkers do not permit direct identification of the plant family and/or genus and mainly record compositions of local plant remains, while pollens mainly reflect the regional vegetation change. Bio-markers and pollen records complement each other, providing a better picture of local and regional environments. Furthermore, biomarkers are more sensitive than pollen to climatic and vegetational change. Several climatic events are clearly identified by the n-alkane biomarker proxies, such as C31/(C27+C29+C 31) ratio and can be correlated to the North Atlantic Heinrich event, B/A, YD and two dry-cool events during the early Holocene such as the periods of 9850 to 9585 cal a B.P. and 8590 to 7920 cal a B.P. These events are consistent with those found in the surrounding regions, suggesting that the regional climate was coupled with global-scale abrupt climatic events. Our results suggest that biomarker and pollen data can record the more detailed climate and vegetation information, thus im-proving the resolution and precision of vegetation and climate reconstruction.
