4.4. Bathyarchaeia co-occurred with methanogens and ammonia oxidizers
Genomic analysis suggested that Bathyarchaeia may play a crucial role in global carbon and nitrogen cycling (Zhou et al. 2018). In this study, we found the interactions between Bathyarchaeia and other archaea were very complex, and Bathyarchaeia play an important role in the construction of the archaeal network (Fig. 5a). The co-occurrences of Bathyarchaeia and acetate methanogens, including Methanosarcinia and Methanobacteria , were also found in other environmental habitats. These results suggest thatBathyarchaeia can be involved in carbon cycling by producing acetate for the heterotrophic microbes and acetoclastic methanogens, and acetate might be the bridge associating the interactions betweenBathyarchaeia and Methanosarcinia (Xiang et al. 2017; Zou et al. 2020). The co-occurrences of Bathyarchaeia and hydrogen Methanogens were also found in paddy soils in this study. These results suggested that Bathyarchaeia might be involved in carbon cycling differently and play a crucial role in the carbon cycle in arable soils.
Bathyarchaeia also frequently co-occurred with members ofNitrososphaeria (Fig. 5d), which is consistent with the results of the global meta-analysis (Xue et al. 2023). Nitrososphaeria is a group of ammonia-oxidizing archaea highly abundant in rice rhizosphere soil with fertilization (Tang et al. 2019). Ammonia oxidizing archaea plays an important role in the soil nitrogen cycle, catalyzing the first step of the ammonia oxidation process (Baker et al. 2020). Genomic studies suggest that Bathyarchaeia may be involved in the nitrogen cycle, and genes involved in ammonia and urea production were found in Bathyarchaeial MAGs (Pan et al. 2020). Thus,Bathyarchaeia was suggested as a transfer station for nitrogen compounds in the global nitrogen cycle (Pan et al. 2020). Additionally, the metagenomic analysis showed that Nitrososphaeraceae contain genes involved in urea degradation, indicating that Bathyarchaeiamay interact with Nitrososphaeraceae via urea production and transformation (Wu et al. 2021). Agricultural systems depend on significant nitrogen fertilizer inputs for farm yield; therefore, the role of Bathyarchaeia in agricultural soils on the nitrogen cycle warrants further research.
We also found that Bathyarchaeia indicated higher niche overlap with other archaea than other archaea. Higher overlap means higher association with other microorganisms, whereas no higher competition was found in paddy soils. This view is supported by network analysis thatBathyarchaeia plays a crucial role in the structure of a network (de Boer & Prins 1990; Holt 1987). In the future, more research is needed to investigate the ecological function of Bathyarchaeia in paddy soils.