Transfer of 13 C between paired Douglas-fir seedlings reveals plant kinship effects and uptake of exudates by ectomycorrhizas.

Processes governing the fixation, partitioning, and mineralization of carbon in soils are under increasing scrutiny as we develop a more comprehensive understanding of global carbon cycling. Here we examined fixation by Douglas-fir seedlings and transfer to associated ectomycorrhizal fungi, soil microbes, and full-sibling or nonsibling neighbouring seedlings. Stable isotope probing with 99% 13 C-CO2 was applied to trace 13 C-labelled photosynthate throughout plants, fungi, and soil microbes in an experiment designed to assess the effect of relatedness on 13 C transfer between plant pairs. The fixation and transfer of the 13 C label to plant, fungal, and soil microbial tissue was examined in biomass and phospholipid fatty acids. After a 6 d chase period, c. 26.8% of the 13 C remaining in the system was translocated below ground. Enrichment was proportionally greatest in ectomycorrhizal biomass. The presence of mesh barriers (0.5 or 35 µm) between seedlings did not restrict 13 C transfer. Fungi were the primary recipients of 13 C-labelled photosynthate throughout the system, representing 60-70% of total 13 C-enriched phospholipids. Full-sibling pairs exhibited significantly greater 13 C transfer to recipient roots in two of four Douglas-fir families, representing three- and fourfold increases (+ c. 4 µg excess 13 C) compared with nonsibling pairs. The existence of a root/mycorrhizal exudation-hyphal uptake pathway was supported.

Inter-plant communication through mycorrhizal networks mediates complex adaptive behaviour in plant communities.

Adaptive behaviour of plants, including rapid changes in physiology, gene regulation and defence response, can be altered when linked to neighbouring plants by a mycorrhizal network (MN). Mechanisms underlying the behavioural changes include mycorrhizal fungal colonization by the MN or interplant communication via transfer of nutrients, defence signals or allelochemicals. We focus this review on our new findings in ectomycorrhizal ecosystems, and also review recent advances in arbuscular mycorrhizal systems. We have found that the behavioural changes in ectomycorrhizal plants depend on environmental cues, the identity of the plant neighbour and the characteristics of the MN. The hierarchical integration of this phenomenon with other biological networks at broader scales in forest ecosystems, and the consequences we have observed when it is interrupted, indicate that underground 'tree talk' is a foundational process in the complex adaptive nature of forest ecosystems.