Tracing the spatial extent and lag time of carbon transfer from Picea abies to ectomycorrhizal fungi differing in host type, taxonomy, or hyphal development

We used five mature Picea abies continuously labeled with ¹³C-depleted CO₂ in a broadleaf-dominated Swiss forest to assess the spatial extent and lag time of carbon fluxes to ectomycorrhizal fungi differing in hyphal development and host association. We traced labeled carbon into ectomycorrhizal sporocarps collected for two seasons at different distances from labeled Picea. Picea-derived photosynthate reached conifer-specific sporocarps up to 6–12 m away and reached other sporocarps only 0–6 m away. At 0–6 m, genera of lesser hyphal development acquired more Picea-derived photosynthate than those of greater hyphal development, presumably from preferential fungal colonization of inner root zones by the former genera. Correlations of sporocarp δ¹³C with daily solar radiation integrated for different periods indicated that carbon fluxes from Picea to sporocarps peaked 17–21 days after photosynthesis. Thus, these results provided rough estimates of the spatial extent and temporal lags of carbon transfer from Picea to ectomycorrhizal fungi.