Dual-Domain Primary Succession of Bacteria in Glacier Forefield Streams and Soils of a Maritime and Continental Glacier

Glaciers retreat rapidly and create newly exposed terrestrial and aquatic habitats in glacier forefields, where primary succession proceeds synchronously in glacier forefields. Here, we introduced the "Dual-Domain Primary Succession" concept to examine the parallel yet distinct primary succession processes in soil and stream ecosystems within glacier forefields, by focusing on Hailuogou Glacier and Urumqi Glacier No.1 in China. Findings showed that soil bacterial communities exhibited higher α-diversity with a decreasing pattern in Hailuogou Glacier, in contrast to Urumqi Glacier No.1, which displayed lower and unimodally distributed α-diversity along the glacier forefield chronosequence (GFC). A similar pattern emerged in streams, except for an increasing α-diversity trend in Urumqi Glacier No.1 stream along the GFC. Additionally, α-diversity in streams changed more rapidly than in soils for Hailuogou Glacier, but more slowly for Urumqi Glacier No.1. Along GFC, both soil and stream bacterial communities experienced spatial variations, primarily due to species turnover. The succession of community composition was evident at the OTU level, with each module in the co-occurrence network consisting of OTUs enriched at specific successional stages. A substantial number of OTUs shared between paired soil and stream samples showed a decreasing trend along the GFC, while β-diversity increased. The results suggested that bacterial communities have a similar succession pattern but in different pace between soil and stream while having distinct successional trajectories between the studied glaciers. This study highlighted the "Dual-Domain Primary Succession" in glacier forefields, but further studies with more glaciers are necessary to make broader generalizations.