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The discipline of "Bio-Organic Geochemistry" is a cross research field between biogeochemistry and traditional organic geochemistry, which focuses on geochemical processes related to the biosynthesis of organic molecules (particularly lipids) by (micro) organisms, organic matter production by primary producers, degradation of organic matter by microbial processes recorded by retainable lipid biomarkers, and organic proxies for studies of paleo-climate, paleo-environments, paleoecology and Earth evolution. This field aims to go beyond the traditional petroleum-oriented Organic Geochemistry by integrating with biogeochemical concepts concerned mostly with biomolecules from cellular material such as DNA and lipids. A formal Chinese organization in Bio-Organic Geochemistry was established in 2012 when the first conference was held in Guangzhou. This organization has witnessed rapid growth over the past six years with focused research addressing organic proxies in paleoclimate and paleoenvironmental applications, with particular rapid development in glycerol dialkyl glycerol tetraethers-derived proxies. Most progresses in China so far are made following or paralleling the international trend in biogeochemical studies. Things have begun to change with China's ambitious initiatives in several bio-geo programs such as the Ocean Deep Drilling Program of China, the Microbial Hydrosphere Program, the Deep Carbon Observatory, and the Microbiome Program. Looking forward in the 21st Century, the growing Chinese research community in Bio-Organic Geochemistry faces grand opportunities and challenges as Chinese scientists propel themselves toward global research frontiers. [ABSTRACT FROM AUTHOR]

Glycerol dialkyl glycerol tetraethers (GDGTs) in lake sediments are useful biomarkers for the continental paleoclimatic reconstruction. However, the environmental controls on the distribution of these compounds, in particular the 6-methyl isomers of bacterial branched GDGTs (bGDGTs), in the lakes with contrasting pH, are still unknown, hindering their application for paleo-reconstructions. Here, we investigated the environmental impacts on the distribution of GDGTs in 17 alkaline lakes and 1 acid lake in China. It was found that the dissolved oxygen content in water column may have an impact on the distribution of archaeal isoprenoid GDGTs (iGDGTs) by causing the change in archaeal communities. The ratio of GDGT-0/crenarchaeol increases with decreasing oxygen content, indicating that the relative abundance of anaerobic methanogenic archaea or Miscellaneous Crenarchaeotic Group (MCG) vs. aerobic Thaumarchaeota is controlled by the oxygen content dissolved in water of these lakes. Thaumarchaeota are likely to contribute only a small proportion of iGDGTs in the relatively oxygen-depleted lakes, and thus TEX is not suitable for the reconstruction of the surface temperature of these lakes. The abundance ratio of iGDGTs to bGDGTs ( R) appears to show no relationship with water pH in all the lakes, but exhibits a significant positive correlation with the water depth of the acid Lake Qinghai in Tengchong. As expected, the methylation degree of bGDGTs (MBT′) was found to correlate with both mean annual air temperature (MAT) and water pH, and the cyclization degree of bGDGTs (CBT) correlates only with water pH in these lakes. However, the MBT′, an index to measure the methylation degree of 5-methyl bGDGTs, exhibits no relationship with MAT, whereas MBT′, the methylation degree of 6-methyl bGDGTs, was found to correlate significantly with MAT. This is opposite to the situation observed in the global soils, pointing to a different adaptation of bGDGT-producing bacteria to environmental variables or different microbial sources of bGDGTs in these lakes. The relative abundance of 6- vs. 5-methyl bGDGTs is controlled by pH in these lakes, similar to that observed in worldwide soils. Hence, the isomer ratio (IR) of 6-methyl bGDGTs or CBT′ can be used as a proxy for water pH, although they might be influenced by other environmental factors including temperature in the lakes with a narrow range of pH. [ABSTRACT FROM AUTHOR]

The distributions of microbial tetraether lipids, i.e. glycerol dialkyl glycerol tetraethers (GDGTs), were investigated in a variety of Chinese soils featured by a wide range of pH values in different climate zones. The bacterial branched GDGTs and archaeal isoprenoid GDGTs were found to be widely distributed in Chinese soils and their relative abundance was controlled primarily by soil pH. The bacterial bGDGTs usually dominate over archaeal iGDGTs in abundance when the soil pH is below 8.0. However, archaeal iGDGTs become dominant and the abundance of halophilic archaea characterized by GDGT V without cyclopentyl ring increases dramatically in the alkaline soil with pH greater than 8.0. The relative abundance of archaeal iGDGTs to bacterial bGDGTs was defined here as RAI index. The RAI index decreases with elevated soil pH and a linear correlation is found between them, indicating that the relative abundance of archaeal iGDGTs to bacterial bGDGTs increases with increased pH. The RAI index thus could be a novel proxy of the pH values of paleosol. The terrestrial input index, BIT (Branched and Isoprenoid Tetraethers Index), decreases with increased soil pH, suggesting that soil pH should be taken into consideration when the terrestrial contribution to marine sediments is estimated by BIT index. Moreover, the TEX86 index cannot be used to reconstruct sea surface temperature in the sediments featured by a large terrestrial input. [ABSTRACT FROM AUTHOR]