Comammox bacteria and ammonia oxidizing archaea are major drivers of nitrification in glacier forelands.

• Succession of soil ammonia oxidizing microorganisms during glacier degradation. • Nitrification related gene abundance tended to increase with glacier retreat. • Comammox were the most abundant group of ammonia oxidizers in glacier forelands. This study investigated the abundance of comammox bacteria and canonical ammonia-oxidizing bacteria (AOB) and archaea (AOA), and their relative contribution to nitrification along a chronosequence of deglaciated forelands. The results showed that nitrification related gene abundance tended to increase with glacier retreat, with comammox bacteria and AOA appearing to be the most critical drivers for soil nitrification rates. These findings provide new evidence for the presence of comammox bacteria in glacier forelands and enhance our understanding of the niche differentiation of canonical nitrifier and comammox bacteria. [ABSTRACT FROM AUTHOR]