Gram-negative bacterial 3-hydroxy fatty acids (3-OH-FAs) 20 biomarkers are widespread in a variety of environments including both marine 21 and terrestrial sediments (including speleothems). In this study we analysed 22 the hydroxylated membrane lipids of 26 soil samples from an altitudinal 23 transect of Shennongjia Mountain (Mt.) in central China to study the 24 environmental factors controlling the relative distribution of 3-OH-FAs. Our 25 results show that both the ratio of the summed iso and anteiso to the total 26 amount of normal 3-OH-FAs (RIAN), and the ratio of summed iso and anteiso 27 to the total amount of all 3-OH-FAs (Branched Index) were primarily related to 28 the pH of soil (R 2 = 0.70 and 0.70, respectively). Additionally, the anteiso to 29 normal 3-hydroxy fatty acids ratio of the C15 and C17 homologues (RAN15 and 30 RAN17) shows a significant negative correlation with mean annual air 31 temperature (MAAT) (R 2 =0.51 and 0.48, respectively). When comparing the 3-32 OH-FA based indices with established glycerol dialkyl glycerol tetraether 33 (GDGT) based indices from the same soil samples, the RIAN and Branched 34 Index show strong linear correlations with the cyclisation ratio of branched 35 tetraethers (CBT) (R 2 = 0.77 and 0.74, respectively), and the RAN15 and RAN17 36 show negative correlations with the MBT/CBT-MAAT (MBT, methylation index 37 of branched tetraethers) (R 2 = 0.61 and 0.36, respectively). Our new field-based 38 correlations demonstrate the physiological response of Gram-negative bacterial 39 cell membranes to the external environment and suggest that 3-hydroxy fatty 40 3 acids can be applied in palaeoenvironmental studies to estimate past MAAT 41 and soil pH.

To achieve a sufficient understanding of the spatial dynamics of terrestrial climate variability, new proxies and networks of data that cover thousands of years and run up to the present day are needed. Here we show the first Gram-negative bacterial 3-hydroxy fatty acid (3-OH-FA) based temperature and hydrological records from any palaeoclimate archive globally. The data, covering the last 9 ka before present (BP), are generated from an individual stalagmite, collected from Heshang Cave, located on a tributary of the Yangtze River, central China (30°27′N, 110°25′E; 294 m). Our results indicate a clear early-to-middle Holocene Climatic Optimum (8.0-6.0 ka BP) followed by a long-term monotonic cooling and increasing variability over the last 0.9 ka BP. The hydrological record shows two relatively long wet periods (8.8-5.9 ka BP and 3.0-0 ka BP) and one relative dry period (5.9-3.0 ka BP) in central China. We show that 3-OH-FA biomarkers hold promise as independent tools for palaeoclimate reconstruction, with the potential to deconvolve temperature and hydrological signals from an individual stalagmite.

Mendez-Millan et al., 2010). In order to acclimatize to the specific conditions of peatlands (waterlogged, nutrient poor and partly anoxic and acidic), plants develop shallow but flourishing root systems (Rydin and Jeglum, 2006), which can contribute high amount of lipids to peat deposits. To date, only Pancost et al. (2002) noted the root-derived lipids from peat-forming plants.A number of studies have reported the lipid compositions of peatland plant communities (Ficken et al., 1998;Nott et al., 2000;Pancost et al., 2002;Nichols et al., 2006). These communities were distributed in Europe and North America, while the results in other regions were not available in the literature to the best of our knowledge. In addition, except for the peat moss (Sphagnum species) shrubs are abundant in the above bogs. In contrast, the Dajiuhu Peatland is characterized by Sphagnum palustre and various herbaceous plants. It is, therefore, worth assessing the lipid composition of the plant community in such an herb peatland. The n-alkane distributions of several moss species (S. palustre, Aulacomnium palustre, Polytrichum commune and Hypnum revolutum) from the area have been previously reported by Huang et al. (2010 (Received November 16, 2010; Accepted April 30, 2011) The main aim of this study was to assess the free lipid composition of plant community in a Chinese peatland. Twelve plant species from the Dajiuhu Peatland were analyzed for the compositions of n-alkanes, n-fatty alcohols and sterols in leaves and roots. The lipid compositions are significantly different between root and leaf for most plants. In some cases, the roots yield more long chain n-alkanes and n-alkanols than the leaves of the corresponding plant. The long chain nalkanes of the roots in half of the plant species are characterized by a higher C max (homologue with the maximum concentration) relative to the leaves. The root-derived sterols and steroidal ketones may be important sources for corresponding compounds within the peat. Because of the different lipid compositions of roots and leaves, more attention should be paid to root-derived lipids for investigations of the lipid composition and their source assessment in soils and terrestrial sediments, where root-derived organic matter can be an important source. The contribution of root-derived lipids may be especially important in peatlands, where acidic and/or anoxic conditions in the subsoil limit the degradation of organic matter and the contribution of leaf litter.