Resource transfer between plants through ectomycorrhizal fungal networks

Abstract

Carbon (C), nutrients and water (H2O) have been known for five decades to flow between plants through ectomycorrhizal (EM) networks. This flux has the potential to affect plant and fungal performance and resource distribution within communities. We asked two questions: (1) What are the pathways and mechanisms for C, nutrient and H2O fluxes between plants through EM networks? (2) What are the magnitude, fate and importance of C, nutrient and H2O transfer among EM plants? Mycorrhizal networks provide a distinct pathway for resource fluxes among plants and mycorrhizal fungi, partitioning them away from other competing soil microbes and plant roots in the soil matrix, and potentially providing a competitive advantage (or disadvantage) for some individuals involved in the network. Carbon and nutrients flow symplastically and apoplastically through mycorrhizal symbionts, hyphae and rhizomorphs along source-sink gradients across the networking mycelia and plant community. EM networks can also facilitate the hydraulic redistribution of soil or plant water following water potential gradients. Carbon fluxes through EM networks have been shown to supply 0–10 % of autotrophic, up to 85 % of partial myco-heterotrophic (MH), and 100 % of fully MH plant C. This C supply has been loosely associated with the increased survival and growth of autotrophic plants, but has been shown to be essential for the survival of MH plants. Network-mediated nitrogen (N) fluxes between N2-fixing and non-N2-fixing plants have supplied up to 40 % of receiver N, and this has been associated with increased plant productivity. Fluxes between non-N2-fixing plants have supplied <5 % of receiver N. Hydraulic redistribution involving EM fungi has supplied up to 50 % of plant water; this has been shown as essential for plant survival in some cases. However, uncertainty remains as to how much of this water transfers through EM networks. Phosphorus transfer through EM networks has not been adequately demonstrated. Overall, this review chapter shows that resource fluxes though EM networks are sufficiently large in some cases to facilitate plant establishment and growth. Resource fluxes through EM networks may thus serve as a method for interactions and cross-scale feedbacks in the development of plant-microbial communities. The outcome of resource transfer through EM networks for the stability of terrestrial ecosystems depends upon the environmental context.