Microbial succession and glnA gene enrichment from supraglacial debris to recently deglaciated forefields

Debris-covered glaciers represent unique and ecologically significant cryo-ecosystems that are rapidly evolving under climate change pressures. These environments, characterized by their supraglacial debris layers, create distinct habitats that support specialized microbial communities and influence nutrient cycling processes. Despite their importance in high-altitude regions, the microbial-driven nitrogen cycling mechanisms that facilitate ecosystem development following glacier retreat remain insufficiently understood.We conducted a comprehensive investigation along the debris gradient of the rapidly receding Hailuogou Glacier on the southeastern Tibetan Plateau. Our multidisciplinary approach integrated full-length 16S rRNA and ITS amplicon sequencing with metagenomic analysis to characterize bacterial and fungal communities and their functional potential for nitrogen cycling. Sampling spanned from supraglacial zones through proglacial areas to recently deglaciated forelands, capturing the complete ecological transition from ice-covered to vegetated environments.Our results demonstrate a clear successional pattern in microbial community structure and function. Bacterial diversity showed a significant increase toward the glacier terminus, while fungal diversity exhibited a substantial decline following plant establishment in the foreland. Metagenomic analysis revealed a crucial functional shift in nitrogen cycling pathways: genes associated with nitrification and denitrification (including amoA, nirK, and nosZ) predominated in barren supraglacial debris. Conversely, the key ammonium assimilation gene glnA (glutamine synthetase) showed significant enrichment in proglacial debris, with further increases observed following pioneer plant colonization.The observed enrichment of ammonium assimilation genes suggests a sophisticated microbial adaptation strategy in response to glacier retreat. This functional shift from nitrogen loss pathways to nitrogen assimilation and conservation mechanisms represents a crucial ecological transition that likely facilitates early soil formation and supports primary succession in nutrient-poor environments. The differential response patterns between bacterial and fungal communities highlight their distinct ecological roles in these evolving ecosystems. The identified patterns of microbial succession and functional gene enrichment offer valuable insights for predicting the ecological trajectories of high-altitude cryo-ecosystems under ongoing climate change.