Denitrifying anaerobic methane oxidizing in global upland soil: Sporadic and non-continuous distribution with low influence

Both the distribution and contribution of denitrifying anaerobic methane oxidation (damo) have been extensively reported in enrichment culture and aquatic ecosystems; yet, the role of damo in upland soil remains unclear. In the present study, this role of damo bacteria in global upland soils was investigated via isotope tracing technique, quantitative PCR assay, and clone library construction, targeting both 16S rRNA and functional pmoA genes. Using samples from the surface (0-20 cm, n = 148) and deep soil profiles (from 0 to 70-6300 cm, n = 160), the damo bacterial distribution seemed to be sporadic in surface soils and non-continuous in soil profiles. The moisture content of the upland soils seems to be the key factor to influence damo occurrences. Among soil profiles with higher moisture content, the highest damo bacterial abundance of 4.62 x 10(6) copies g(-1) soil was detected at 180-200 cm depth in Xingtai, China. Both a shift of damo bacterial community structure was observed with depth as well as strong temporal heterogeneity within surface soils. Damo activity (0.18 nmol C g(-1) h(-1)) was only detected in the summer surface soil (0-20 cm) of Xingtai. The global distribution of damo in upland soils indicates that upland soils are not favorable environments for the occurrence of damo processes, and the potential role of damo in upland soils might have a limited contribution to the global CH4 cycle.