Figure legends
Fig. 1. Experimental design. (a) We grew two host plants ofMedicago truncatula in an elongated box divided into three compartments by nylon mesh. The focal plant grew in the focal compartment and was inoculated with Rhizophagus irregularisstrain A5 (A5). The partner plant grew in the partner compartment and was inoculated with either A5, R. irregularis strain B12 (B12) orRhizophagus aggregatum (Agg). Only the central compartment was supplied with phosphorus (P) in the form of apatite. (b) We grew two host roots of in-vitro Daucus carota on a rectangular plate. The focal host root grew in the focal compartment, and was inoculated with A5. The partner plant grew in the partner compartment and was inoculated with either A5, B12 or Agg. The fungal hyphae from both root systems could cross over the plastic barrier into the central compartment, but the plastic barrier prevented the diffusion of nutrients. We imaged the central compartment in three locations (black squares) to study fungal architecture. (c) Side view of anin-vitro plate in which the central compartment was covered with a cellophane sheet to allow for 2D fungal imaging. (d) Side view of anin-vitro plate without cellophane sheet. The fungal hyphae could cross over the plastic barrier into the medium of the central compartment. We then added quantum-dot apatite to the partner compartment to quantify the transfer of quantum-dot tagged apatite from partner roots across the fungal network and into focal roots.
Fig. 2. Boxplot of intraradical colonization of focal roots and ratio of intraradical colonization of focal plant to partner plant in the whole plant greenhouse experiment. (a) Lower intraradical colonization of focal roots when the fungal network was composed of less-related, non-selfing fungal strains. (b) Focal and partner were colonized equally when network was composed of one strain (A5-A5), there was higher colonization of the focal root when there was a non-selfing partner fungus. Black dotted line indicates a 1:1 ratio. Box-plots with different letters indicate significant difference (p < 0.05), top and bottom of the box indicate the first and third quartile, and the whiskers indicate the minimum and maximum values. n A5 = 8, n B12=9,n Agg=9.
Fig. 3. Boxplots of extraradical fungal abundance and extraradical to intraradical investment ratio in the root organ cultures (a) Total extraradical fungal abundance (sum of all three compartments) is significantly influenced by the fungal strain in the partner compartment, with higher fungal abundance when the network is less related. (b) We found a bias towards intracellular growth when networks were selfing (A5-A5), but more extracellular growth when networks were not selfing. Box-plots with different letters indicate significant difference (p < 0.05), top and bottom of the box indicate the first and third quartile, and the whiskers indicate the minimum and maximum values. n A5=12,n B12=11, n Agg=17.
Fig. 4. Physical architecture of extraradical network . Extraradical mycelium in the fungus-only compartment is plotted from the partner compartment barrier (left) (a), (d), (g) to the center (right) (c), (f), (i), for the three partner fungal strains. (a)-(c) A5 grows a denser and more complex network towards the center of the central compartment, increasing the surface area and theDm . (d)-(f) B12 decreases in density and complexity towards the center of the central compartment. (g)-(i) Agg shows the highest density and complexity near the partner compartment and the least towards the center of the central compartment.
Fig. 5. Boxplots of fungal network efficiency and dry root weight of root organ cultures (a) Quantum-dot-apatite (QD) transfer to the focal roots was less efficient when associated with a less-related fungal network. n A5=12,n B12=8, n Agg=12. (b) We found that the total root mass (focal + partner root) was lower when the fungal network was less related. n A5=12,n B12=12, n Agg=17. Box-plots with different letters indicate significant difference (p < 0.05), top and bottom of the box indicate the first and third quartile, and the whiskers indicate the minimum and maximum values.