Changes in archaeal ether lipid composition in response to agriculture alternation in ancient and modern paddy soils

Paddy soil is the consequence of human activity, which has exerted significant anthropogenic impacts on the global carbon cycle in recent earth history, particularly through the production of microbial methane from paddy soils. However, the anthropogenic impact of rice fields on the distribution of methanogenic archaea and methane emission during human history is poorly documented. Isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) are unique biomarkers for archaea, which can be used to examine changes in climate and environment during human evolution. This study aimed to reconstruct archaeal communities and evaluate how they might have been impacted by human activities during the development of two paddy soil profiles that recorded a cultivation history of over 6300 years in Zhejiang Province, southeastern China. Variations in archaeol, GDGT-0 and crenarchaeol strongly suggest that archaeal ether lipids deeply buried in the ancient paddy soil profiles are mainly fossil records rather than contemporary signals. Cluster analysis based on GDGT compositions revealed two major groups of GDGTs corresponding to different soil types, reflecting the shift of archaeal communities from Thaumarchaeota to methanogens. The archaeal ether lipid-based proxies (MI, archaeol/crenarchaeol and GDGT-0/crenarchaeol) related to methane-producing archaea varied remarkably in different soil types associated with the anthropogenic management. These proxies had significantly higher values in the buried paddy soils than currently cultivated paddy soils, implying that the earlier anthropogenic flooding may have resulted in considerable methane emission from paddy soils in southeastern China. (C) 2019 Elsevier Ltd. All rights reserved.