Carbon and nitrogen control hyphae-mediated bacterial dispersal and partner recruitment in glacier forefield soils

Bacteria can disperse along fungal hyphae, using them as “highways” to cross physical discontinuities in soil (e.g. air-filled pores) and potentially to traverse microsites with suboptimal conditions such as oxygen- or nutrient-limited zones. While laboratory studies have resolved mechanistic aspects of hypha-associated bacterial motility, the ecological and resource-dependent context of this interaction, and its relevance for soil C and N dynamics, remains poorly understood. We address this gap by combining (1) laboratory experiments manipulating carbon and nitrogen sources to test how nutrient regime shapes the dispersal of fungal–bacterial co-communities from mid-Arctic glacier forefield soils (Greenland), and (2) a one-year field colonization experiment in glacier forefields of Greenland, Iceland, and Austria, tracking colonization of initially barren sediments in specially designed columns across geologies and soil development stages.

In the laboratory, distinct C/N combinations promoted exploratory growth by different fungi, with communities dominated by Mucor, Actinomortierella, and Syncephalis. Co-dispersing bacterial communities also shifted with nutrient regime, dominated by Flavobacterium, Janthinobacterium and Pseudomonas. Bacterial diversity transported along hyphae increased under inorganic N supply (ammonium or nitrate) relative to cellulose amendment without added N, indicating that fungal nutritional status and N availability can modulate partner recruitment during dispersal. Field observations complemented these results by revealing how hypha-associated colonization unfolds under natural conditions across contrasting forefields.

Together, our findings show that fungal physiology and nutrient status structure hypha-associated bacterial partnerships and suggest that hypha-mediated translocation can influence microbial community assembly during early soil formation, with implications for C/N acquisition strategies in heterogeneous soils.