The Distributions Of Microbial GDGTs And Its Climate Implications In Peat Deposit Of Ruoergai

Lipid biomarker contains rich information and can sensitively record the detailed information of climate. They have been widely applied to the research of the global change. The research of lipid biomarker in the global climate change is been focused on the higher plants, algae and other ecosystem members of the upper system whereas the microbial ecosystem research is lacking. Microbial lipids can record environmental change on basis of variations of their structures and compositions. In recent years, a series of climate and environmental indicators have been established through the research of GDGTs in oceans, lakes and soil. However, little research on peat microbial lipids and its climate and environmental significance is unclear. Compared to other sediments, peat is characterized by high resolution, abundant organic matter, rich biological communities and powerful ecological functions. Additionally carbon storage of peat in terrestrial ecosystems is the most. These provide very favorable conditions to carry out the work of peat microbial lipids. The study of the Tibetan Plateau peat has achieved many significant results in vegetation and the climate evolution, but the work of ancient microbial lipids is still lacking, it is necessary to carry out the research. This dissertation will focus on microbial lipids from the shallow peat of Ruoergai region in the northeastern Tibetan Plateau.The different compounds and structures of Ruoergai peat GDGTs have been first detected by LC-MS/MS. The distribution characteristics of peat GDGTs and the structure and changes of microbial communities have been discussed, and environmental indicators based on oceans, lakes and soil have been applied to the peat for evaluating the applicability of the different climatic indicators in the peat deposition environment. The relationship between the different climate indicators has been discussed, this provided valuable information for exploring the application of peat GDGTs in climate change. The main findings are as follows.(1)The Ruoergai peat deposit is abundant in GDGTs compounds, of which bGDGTs accounts for79.7%and93.1%of the total GDGTs compounds, more than the archaea iGDGTs content of5to6times. The main types of bGDGTs are bGDGT-I and bGDGT-Ⅱ, followed by bGDGT-Ⅲ. The main types of iGDGTs are GDGT-0and archaeol, followed by GDGT-1～GDGT-3and a very low content of crenarchaeol and crenarchaeol’(2) The main microbial communities are bacteria, the changes of the relative content of the microbial communities are relationship to the changes of peat pH. With more alkaline in the environment, the relative content of archaea are higher whereas the relative content of the bacteria are lower.(3) Methanogenic archaea is the main group of archaea communities. GDGT-0and archaeol as the effective proxies of methanogenic archaea have been verified. This will provide a tool to earth’s cycle of methane biological.(4) Crenarchaeol is mainly derived from ammonia-oxidizing crenarchaeota. The content of crenarchaeol in Ruoergai peat is very low. This shows that ammonia-oxidizing crenarchaeota is not suitable to survive in the acidic and hypoxic environment.(5) The MAT values obtained through TEX86have large errors with the measured values. Therefore, TEX86does not apply to establish the environment indicators in Ruoergai peat. The BIT index of Ruoergai peat is close to1, the BIT value increases with the pH values increases.(6) The pH, MAT, MAP and other climate indicators recorded by the shallow peat of Ruoergai were obtained by bGDGTs environmental factor formula. The changes in pH of Core1and Core2profile are range of5.2to6.5and6.0to6.8. The MAT average value of Core1and Core2profile are respectively0.1℃and2.0℃. The changes in MAP of Core1and Core2profile are range of439～800mm and437～783mm. These values of climate indicators are relatively close to field test results or the environmental record of Ruoergai weather station in recent decades. It can be considered that the bGDGTs series of climate indicators can generally reflect regional climate signals. This indicates that GDGTs of peat deposit has strong applicability and potential applications in high-resolution reconstruction of the terrestrial environment.