Question

For decades, proponents of the 'mycorrhizal cooperation' model argued that subterranean networks of fungal hyphae connecting disparate trees act as communal pipelines, actively redistributing carbon from mature canopy trees to shaded understory seedlings to enhance collective forest resilience. However, recent critical syntheses demonstrate that much of the empirical evidence cited for this bidirectional sharing relies on laboratory isotopic pulse-chase experiments where carbon tracers ($^{13}\text{C}$ or $^{14}\text{C}$) were tracked in closed soil cores without adequately isolating fungal uptake from plant uptake. When fungal mycelium is physically separated from root tissue using micro-mesh barriers that allow hyphae but exclude root contact, the measurable net carbon flux into the receiving seedling's structural tissues drops to levels indistinguishable from background transpiration uptake. This indicates that the fungal partner primarily sequesters carbon within its own biomass as an energetic fee for mineral transfer, rather than routing it altruistically between plant hosts. Furthermore, in mature stands where tree-to-tree connections were verified via genetic microsatellite markers, carbon transfer rates correlated strictly with the physiological sink strength of the receiving root tips rather than any programmatic egalitarian distribution. Thus, apparent resource transfer across common mycorrhizal networks reflects the byproduct of competing individual sink-source gradients and selfish fungal resource allocation rather than cooperative communal buffering.

Based on the passage, which of the following assertions are logically supported inferences? (Select all that apply)