[A-CG46] Biogeochemical Cycles in Land Ecosystem

[ACG46-P08] Soil CO₂ release increase and microbial community shift under dry-wet cycles: Comparison of surface soils and buried humus layers

*Yuri Suzuki¹, Hirohiko Nagano¹, Kazuki Suzuki¹, Syuntaro Hiradate², Jun Koarashi³, Mariko Atarashi-Andoh³, Yukiko Abe³, Masataka Nakayama⁴ (1.Niigata University, 2.Kyushu University, 3.Japan Atomic Energy Agency, 4.Tottori University)

Keywords:Soil microbe, Greenhouse gases, Amplicon sequence, Extreme weather

Recent observations of decreased precipitation frequency and increased intensity are expected to intensify dry-wet cycles (DWC), significantly increasing soil microbial respiration-derived carbon dioxide (CO₂) emissions. Soil microbes play an important role in the dynamics of greenhouse gases, such as methane (CH₄) and nitrous oxide (N₂O). However, there is still much uncertainty in fluctuations in soil microbial communities under DWC, and differences between soils have not been fully clarified. In this study, to elucidate the effect of differences in soil nutrient conditions on microbial community fluctuations under DWC, we conducted incubation experiments using 10 surface soils collected from six forest and grassland sites in Japan, along with 2 surface soils and 2 buried humus layer soils with low carbon availability collected from a forest in Hokkaido. The experimental conditions consisted of control without moisture fluctuation and DWC treatment, where soils were subjected to drying and rewetting for one cycle of 28 days. Microbial community composition was analyzed by targeting bacterial 16S rRNA genes and fungal ITS regions in soil samples taken at the start and end of the incubation experiment. In the surface soils, microbial community composition of bacteria, archaea, and fungi varied not only among soils, but among water treatments. Additionally, in all soils, DWC resulted in common changing patterns with an increase in Actinobacteria relative abundance, a decrease in Acidobacteria for bacteria and archaea, and a decrease in Mortierellomycota for fungi. Furthermore, the total CO₂ emissions during the incubation were significantly higher in the DWC treatment than in the controls in all soils. In the four soils from Hokkaido, CO₂ emissions increased in the DWC treatment at the end of the experiment, and similar microbial community fluctuations to those in the surface soils were observed. However, differences in microbial community composition between the controls and the DWC treatments were particularly pronounced in the buried humus layer, where significant increases in Gammaproteobacteria were observed, showing different patterns of change compared to the surface soils. Furthermore, based on the PICRUSt2 estimation using bacterial 16S rRNA gene sequencing data, the relative abundance of nitrification-related genes involved in N₂O production and genes related to CH₄ production, showed greater changes due to DWC in the buried humus layer than in the surface soils in the Hokkaido four soils. The expected DWC intensification in the future may significantly alter soil microbial communities, particularly in soils with low carbon availability, such as buried humus layers, potentially affecting not only CO₂ emissions but also CH₄ and N₂O dynamics.