Firm Roots in Tibetan Soil

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Soil Organic Matter Fractions under Different Vegetation Types in Permafrost Regions along the Qinghai-Tibet Highway, North of Kunlun Mountains, China

As a key attribute of soil quality, soil organic matter(SOM) and its different fractions play an important role in regulating soil nutrient cycling and soil properties.This study evaluated the soil carbon(C) and nitrogen(N) concentrations in different SOM fractions(light– and heavy fractions,microbial biomass) under different vegetation types and analyzed their influencing factors in continuous permafrost regions along the Qinghai-Tibet Highway in the North of Kunlun Mountains, China.Soil samples were collected in pits under four vegetation types — Alpine swamp meadow(ASM), Alpine meadow(AM), Alpine steppe(AS) and Alpine desert(AD) — at the depth of 0-50 cm.The vegetation coverage was the highest at ASM and AM, followed byAS and AD.The results indicated that the concentrations of light fraction carbon(LFC) and nitrogen(LFN), and microbial biomass carbon(MBC)and nitrogen(MBN) decreased as follows: ASM > AM >AS > AD, with the relatively stronger decrease of LFC,whereas the heavy fraction carbon(HFC) and nitrogen(HFN) concentrations were lower in AS soils than in the AD soils.The relatively higher proportions of LFC/SOC and MBC/SOC in the 0-10 cm depth under the ASM soils are mainly resulted from its higher substrate input and soil moisture content.Correlation analysis demonstrated that aboveground biomass, soil moisture content, soil organic carbon(SOC) and total nitrogen(TN) positively correlated to LFC, LFN, HFC, HFN, MBC and MBN, while p H negatively correlated to LFC, LFN, HFC, HFN, MBC and MBN.There was no relationship between active layer thickness and SOM fractions, except for the LFC.Results suggested that vegetation cover, soil moisture content, and SOC and TN concentrations were significantly correlated with the amount and availability of SOM fractions, while permafrost had less impact on SOM fractions in permafrost regions of the central Qinghai–Tibet Plateau.

Branched tetraether lipids in Chinese soils:Evaluating the fidelity of MBT/CBT proxies as paleoenvironmental proxies

The ubiquitous occurrence of branched glycerol dialkyl glycerol tetraethers(br GDGTs) in soils has allowed development of new proxies for reconstruction of past climate and environment. The methylation and cyclization degrees of br GDGTs, expressed as MBT and CBT, respectively, are reported to be mainly controlled by mean annual air temperature(MAAT) and soil p H. However, the br GDGT-derived temperatures and soil p H scatter widely when data from different environmental conditions are considered. In this study, we collected over 300 soil samples from China, which are representative of humid(Xishuangbanna, Guangzhou, and Shanghai), semi-arid(Dongying) and semi-arid/arid(Lanzhou, Tibetan Plateau) regions. Collectively we have the most extensive dataset that broadly characterizes the distribution of br GDGTs according to climate zones in China. The overall data demonstrate that the MBT/CBT derived temperatures better match the measured MAATs in humid and non-alkaline regions than those from regions of low MAP(<400 mm/yr) and above neutral soil p H(>7.0–7.5). Similarly, CBT describes soil p H much better in humid and non-alkaline soils than in semi-arid/arid and alkaline soils; the semi-arid/arid and alkaline soils tend to show a positive correlation between soil p H and CBT, which contradicts that in the humid and non-alkaline soils. While soil p H, MAAT and mean annual precipitation(MAP) are dominating factors controlling the br GDGT distribution across all climate zones, conductivity, total organic carbon and total nitrogen, as well as soil water content can also play an important role locally. Removing br GDGT-II resulted in a revised CBT index that provides more accurate estimation of p H, especially in semi-arid/arid and alkaline soils. The overall Chinese dataset demonstrates that continental air temperature derived from br GDGT-proxies can vastly deviate from real measurements and should be used with extreme caution in paleo-climate or-environment studies.

Distribution of GDGTs in lake surface sediments on the Tibetan Plateau and its influencing factors

Quantitative paleotemperature records are vital not only for verifying and improving the accuracy of climate model simulations, but also for estimating the amplitude of temperature variability under global warming scenarios. The Tibetan Plateau(TP) affects atmospheric circulation patterns due to its unique geographical location and high elevation, and studies of the mechanisms of climate change on the TP are potentially extremely valuable for understanding the relationship of the region with the global climate system. With the development of biomarker-based proxies, it is possible to use lake sediments to quantitatively reconstruct past temperature variability. The source of Glycerol Dialkyl Glycerol Tetraethers(GDGTs) in lake sediments is complex, and their distribution is controlled by both climatic and environmental factors. In this work, we sampled the surface sediments of 27 lakes on the TP and in addition obtained surface soil samples from six of the lake catchments. We analyzed the factors that influence GDGT distribution in the lake sediments, and established quantitative relationship between GDGTs and Mean Annual Air Temperature(MAAT). Our principal findings are as follows: the majority of GDGTs in the lake sediments are b GDGTs, followed by crenarchaeol and GDGT-0. In most of the lakes there were no significant differences between the GDGT distribution within the lake sediments and the soils in the same catchment, which indicates that the contribution of terrestrial material is important. i GDGTs in lake sediments are mainly influenced by water chemistry parameters(p H and salinity), and that in small lakes on the TP, TEX_(86) may act as a potential proxy for lake p H; however, in contrast b GDGTs in the lake sediments are mainly controlled by climatic factors. Based on the GDGT distribution in the lake sediments, we used proxies(MBT, CBT) and the fractional abundance of b GDGTs(f_(abun)) to establish calibrations between GDGTs and MAAT, respectively, which potentially provide the basis for paleoclimatic reconstruction on the TP.