Determining the nutritional importance of common mycelial networks in a desert truffle mycorrhizal symbiosis for soil nitrogen redistribution

In semi-arid soils, limited water and nitrogen (N) restrict biological activity and plant growth. As aridity increases, understanding mycorrhizae’s role in supporting plant communities and mitigating desertification is critical, especially that of common mycelial networks (CMN) linking an individual fungus with roots of multiple plants of the same or different species, impacting establishment, succession, and resilience. Although CMN research has been extensive in temperate forests and grasslands, its importance in semi-arid environments is still uncertain. This study aimed to determine whether CMN shared by semi-arid-adapted plants can assist in redistributing N from nutrient-rich sites to poor ones. We hypothesize CMN are an essential mechanism responding to spatial soil nutrient heterogeneity in semi-arid areas, aiding plant establishment and survival. Complementary controlled experiments were conducted using compartmentalized mesocosms where only mycelia could mobilize nutrients, examining CMN 15 N redistribution and whether plant age/size affects directionality. We used Helianthemum almeriense as the host plant forming an ectendomycorrhiza with the mycorrhizal fungus Terfezia claveryi . Experiments revealed 15 N translocation to sink compartments at varying levels, with higher translocation where plants were present. Moreover, 15 N contribution to plant N pools was significantly higher in 1-month-old seedlings versus adult plants. Under controlled conditions, hyphae appear as an effective conduit for N redistribution. The results provide initial evidence that CMN may help to redistribute N between rich and poor sites in semi-arid regions. Furthermore, the CMN may contribute to the survival of new mycorrhizal seedlings developing in desert truffle plantations or wild areas. This, in turn, advances knowledge on maintaining these ecosystems over time. • First evidence of a common mycelial networks (CMN) redistributing nitrogen and facilitating significant N uptake in semi-arid adapted plants • Under controlled conditions, N translocation to sink compartments varies with plant presence, indicating active roles of CMN in N redistribution • Mycelial networks effectively move N, suggesting CMN are vital for seedling survival and desert truffle ecosystems • Seedlings linked by CMN showed a higher relative growth rate, benefiting disproportionally from N transfer compared to adult plants