The Spatial Extent of Carbohydrate Sharing in the Wood-Wide Web Varies with Climate and with Taxonomy of Ectomycorrhizal Fungi : Insights from the Swiss Forest FACE

∙ To assess how belowground mycorrhizal networks may share resources, we used δ¹³C, δ¹⁵N, and C/N measurements to calculate spatial and temporal dynamics of carbohydrate and amino acid movement through ectomycorrhizal networks of mature trees.

∙ Canopies of 14 deciduous trees were continuously labeled with ¹³C-depleted CO₂ from 2001-2005 (Swiss Forest FACE) and the ¹³C label traced into ectomycorrhizal sporocarps.

∙ Sporocarps derived 69±5%, 30±6%, and 16±7% of their carbon from labeled trees in the elevated (beneath labeled trees), 0-6 m, and 6-12 m distances, respectively. Sporocarp δ¹³C correlated positively with C/N under elevated CO₂ and negatively elsewhere, reflecting that high-δ¹³C carbohydrates from surrounding trees contributed to sporocarps under elevated CO₂ and low-δ¹³C carbohydrates from elevated CO₂ trees contributed to sporocarps elsewhere. Sporocarp δ¹⁵N increased in Cortinarius with decreasing δ¹³C, suggesting that greater hyphal growth with elevated CO₂ sequestered ¹⁵N-depleted N from sporocarp formation. Sporocarp log_e C/N decreased during the 2004 growing season and the contribution of ¹³C-depleted carbon from elevated CO₂ plants decreased at the 0-6 m and 6-12 m distances, suggesting decreased carbohydrate availability and network transport that year. In contrast, sporocarp log_e C/N increased during the 2005 growing season and the contribution of ¹³C-depleted carbon from elevated CO₂ plants increased at the 0-6 m distance, suggesting increased carbohydrate availability and network transport that year. Relative to other taxa, elevated CO₂ reduced C/N by 15% and ambient CO₂ increased C/N by 5% in taxa exclusively associated with deciduous trees, suggesting increased carbohydrate sharing by the deciduous-associated taxa.

∙ These patterns indicated that 1) carbohydrates (high C/N), not amino acids (low C/N), were preferentially transferred between regions differing in source δ¹³C, 2) sporocarp C/N reflected yearly plant productivity, 3) network transport was influenced by climate, and 4) taxonomy influenced transport dynamics belowground.