147 / 2025-04-09 17:20:20

Effects of different dry and wet paleoclimatic conditions on the occurrence of organic carbon: A case study of peat and loess

peat; Loess; dry and wet paleoclimate; Geological lipids

Theme 4: Microbial and Biogeochemical Evolution through Time > Session 4e: Microbial Lipid Biomarkers and Their Isotopes in Environment, Biology, and Evolution

As two key processes on the surface of the earth, the carbon cycle and the water cycle are closely linked, which together affect global carbon storage and climate change. Understanding how hydrological conditions act on carbon storage patterns is critical to understanding the carbon cycle and its potential impact on climate in the context of global change. Traditionally, a humid environment has been thought to be conducive to organic carbon accumulation, but new research suggests that refractory bound organic matter formed by the combination of microbial lipids and soil minerals under drought conditions may be more conducive to long-term preservation.

In this paper, we focused on loess and peat, two typical media in the context of dry and wet paleoclimates, selected samples covering the key periods of dry and wet transitions, extracted free and bound lipids by different methods, analyzed the change characteristics of microbial organic carbon in the two media, and compared the differences in carbon storage forms between the two media, so as to provide theoretical support for the understanding of the water-carbon cycle and the prediction of climate change.

The results show that: (1) Although the distribution of plant-derived n-alkanes in loess and peat is different, the proportion and trend of free state and bound state are similar, and they are basically not affected by the change of dry and wet paleoclimate. (2) In loess, archaeal cell membrane lipids tend to exist in a bound state during extreme drought, indicating that archaea obtain a water-containing microenvironment by tightly binding with minerals. However, the proportion of binding states of bacterial cell membrane lipids varies significantly with dry and wet, and the A series and III.5ME series tend to be more bound in drought time. (3) The form of lipid occurrence in the cell membrane of archaea in peat changed greatly, the bound GDGT-0 increased during drought, and the crenarchaeol decreased, reflecting the adaptation strategies of archaea to the environment with different ecological needs. The bacterial a series and the III.5ME series also tended to bind during drought. (4) Compared with loess and peat, the proportion of peat-bound organic matter increased more significantly during the drought period, but the change of dryness and wetting had a greater impact on the transformation of bacterial cell membrane lipids to bound state in loess, resulting in a decrease in the accuracy of microbial proxy indicators.

In summary, this study reveals the specific effects of dry and wet paleoclimatic conditions on specific forms of organic carbon occurrence, highlights the complexity of microbial and mineral interactions under extreme climate conditions, and provides a new perspective for in-depth understanding of carbon cycle mechanisms and prediction of future climate change. These findings not only improve our understanding of the dynamics of the carbon cycle, but also provide a scientific basis for assessing the impact of climate change on ecosystems and formulating coping strategies. Future research should further explore the evolution of microbial community structure under different climatic conditions and its long-term effects on the carbon cycle, so as to more accurately predict and respond to climate change challenges.